Antisurge Controller forAxial & Centrifugal Compressors [CCC Book].pdf

U

GLOBAL

SUPPLIERS

OF

TURBINE

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COMPRESSOR

CONTROL

SYSTEMS

A/D

RAM

PID

ID

F

IM301 Series 3 Plus Antisurge Controlleruser manual

Series 3 PlusAntisurge Controller

for Axial and Centrifugal Compressors

Publication IM301 (6.1.3)Product Version: 756-004

September 2005

4725 121st Street

Des Moines, Iowa 50323, U.S.A.

Phone: (515) 270-0857

Fax: (515) 270-1331

Web: www.cccglobal.com

Documentation Feedback Form

http://www.cccglobal.com

http://www.cccglobal.com

http://www.cccglobal.com/products.asp

© 1987-2003, Compressor Controls Corporation. All rights reserved.

This manual is for the use of Compressor Controls Corporation and is not to be reproduced without written permission.

Air Miser, Guardian, Recycle Trip, Reliant, Safety On, SureLink, TTC, Total Train Control, TrainTools, TrainView, TrainWare, Vanguard, Vantage, WOIS, and the TTC and impeller logos are registered trade-marks; and COMMAND, TrainPanel, and the Series 3

++

and Series 5 logos are trademarks of Compressor Controls Corporation. Other company and product names used in this manual are trademarks or registered trademarks of their respective holders.

The control methods and products discussed in this manual may be covered by one or more of the following patents, which have been granted to Compressor Controls Corporation by the United States Patent and Trademark Office:

4,949,276 5,347,467 5,508,943 5,609,4655,622,042 5,699,267 5,743,715 5,752,3785,879,133 5,908,462 5,951,240 5,967,7426,116,258 6,217,288 6,317,655 6,332,3366,494,672 6,503,048

Many of these methods have also been patented in other countries, and additional patent applications are pending.

The purpose of this manual is only to describe the configuration and use of the described products. It is not sufficiently detailed to enable outside parties to duplicate or simulate their operation.

The completeness and accuracy of this document is not guaranteed, and nothing herein should be construed as a warranty or guarantee, expressed or implied, regarding the use or applicability of the described products. CCC reserves the right to alter the designs or specifications of its products at any time and without notice.

Series 3 Plus Antisurge Controller

3

Document ScopeThis manual tells how to configure, tune, and operate a Series 3 Plus Antisurge Controller. It does not tell how to install or maintain it (see the Series 3 Plus Hard-ware Reference manual [IM300/H]), nor how to program a DCS to use its Modbus interface (see the Series 3 Plus Modbus Reference manual [IM300/M]).

Chapter 1 summarizes this controller’s applications and features.

Chapter 2 describes the operation of the Antisurge Controller.

Chapter 3 tells how to configure the analog and discrete inputs and outputs and serial communication ports.

Chapter 4 tells how the Antisurge Controller calculates the values of various process conditions.

Chapter 5 tells how to set up the proximity-to-surge calculation and fallbacks.

Chapter 6 tells how to set up the algorithms that calculate various control responses and select the required recycle flow rate.

Chapter 7 describes the additional features used to protect multisection and networked compressors from surge.

Chapter 8 tells how the valve position and actuator control signal are derived.

Chapter 9 tells how to set up the Antisurge Controller’s automatic sequencing, manual operation, and redundant control features.

Appendix A describes each Antisurge Controller configuration parameter.

Appendix B describes the controller test procedures that can be executed from the Engineering Panel.

Appendix F describes each fA mode of the standard Antisurge Controller that is currently recommended for general use. Appendix FS provides basic documentation of application functions that are not recom-mended for general use.

Glossary/Index defines and references various topics discussed in this manual.

Finally, the following supporting documents are included at the back of this manual:

DS301/D lists and describes the default data items that the Series 3 Plus OPC Server provides for this controller.

DS301/M lists this controller’s Modbus coils, discrete bits, and registers.

DS301/O describes the controller’s Front-Panel operator interface.

DS301/V describes the changes to each standard release of this controller.

FM301/C lists the configuration and tuning parameters by key sequence, organized by data group and page.

FM301/L lists the configuration and tuning parameters by name, grouped according to the associated controller feature.

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Contents

Document Conventions

September 2005 IM301 (6.1.3)

The document title appears in the header of each odd-numbered page, while the chapter or appendix title appears in the header of even-numbered pages. Odd-page footers list the document number and revision level [IM301 (6.1.3)], while even-page footers provide the publication date (September 2005).

Acronyms are defined in the sections of this manual that discuss the corresponding subjects, by placing them in parentheses following the spelled-out terms they represent. As an example, a three-letter acronym (TLA) is a way to represent a three-word subject by com-bining and capitalizing the initial letters of those three words. Most are also listed under Symbols and Acronyms on page 10.

Cross-references to other documents specify a section and chapter, while cross-references between chapters of this document specify a page number. References that do not specify a location are internal to the chapter in which they appear. In computerized versions of this manual, all such references are hot-linked to their target locations and appear in green. Entries in the tables of contents, illustration and table lists, and index are also hot-linked but are not green.

Attention may be drawn to information of special importance by using this text styling or one of the following structures:

Note: Notes contain important information that needs to be emphasized.

Caution: Cautions contain instructions that, if not followed, could lead to irre-versible damage to equipment or loss of data.

Warning! Warnings contain instructions that, if not followed, could lead to personal injury.

The appearance of this electrical hazard warning symbol on CCC equipment or the word Warning appearing in this manual indicates dangerously-high voltages are present inside its enclosure. To reduce the risk of fire or electrical shock, do not open the enclo-sure or attempt to access areas where you are not instructed to do so. Refer all servicing to qualified service personnel.

The appearance of this user caution symbol on CCC equipment or the word Caution appearing in this manual indicates damage to the equipment or injury to the operator could occur if operational proce-dures are not followed. To reduce such risks, follow all procedures or steps as instructed.


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Table of ContentsDocument Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Document Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Table of Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5List of Figures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Symbols and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Chapter 1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Major Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Proximity to Surge Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Fallback Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Control Responses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Limiting Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Valve Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Equivalent Flow Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Load Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Operating States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Automatic or Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Redundant Controller Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Hardware Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Analog and Discrete I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Control Valve Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Serial Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Configuration and Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Chapter 2 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Operator Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Continuous Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Valve Position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Valve Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Surge Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Performance Limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Load Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Sequencing Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Stop State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Purge State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Manual Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Initiating Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Restoring Automatic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Manual Override. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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Contents

Fault Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Tracking States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Output Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36Redundant Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Chapter 3 Input/Output Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37Hardware Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Disabling Input Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37Analog Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Analog-to-Digital Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39Transmitter Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39Signal Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39Process Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Measured Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Analog Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Output Loopback Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Valve Position Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

Discrete Inputs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Discrete Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

Fault Relays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45External Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

Serial Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48ID Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Serial Communication Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Serial Communication Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Modbus Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Chapter 4 Calculated Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Flow Rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

Reduced Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Calculated Flow Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

Dual Flow Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55Control Valve Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Discharge Flow Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . .57Aftercooler Flow Measurement . . . . . . . . . . . . . . . . . . . . . . . . . .57

Mass Flow Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58Compensating Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59Compensating Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

Calculated Variable Displays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60Displayed Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Displayed Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Displayed Net Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

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Chapter 5 Proximity to Surge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Application Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Filtering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Characterizing Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Fixed-Geometry Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . 65Variable-Geometry Compressors . . . . . . . . . . . . . . . . . . . . . . . . 66

Fallback Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Default Output Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Minimum Flow Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Compression Ratio Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Sigma Fallback. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Speed Fallback. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Function 5 Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Adjacent Section Flow Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Valve-Sharing Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Polytropic Head Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Chapter 6 Antisurge Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71Control Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72Recycle Trip Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Safety On Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Tight Shut-Off Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Derivative Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Safety On Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Surge Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Surge Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Antisurge Control Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77PI and RT Signal Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77General PI Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Dead Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78Antisurge PI Response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Recycle Trip Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Pressure Limit Scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Auxiliary Limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Performance Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

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Contents

Chapter 7 Multi-Compressor Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . .85Multisection Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

Equivalent Flow Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . .85Reported Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86Upstream Section Flow Known . . . . . . . . . . . . . . . . . . . . . . . . . .87Downstream Section Flow Known . . . . . . . . . . . . . . . . . . . . . . . .89

Valve Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Networked Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92

Primary Capacity Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93Recycle Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

Port 1 Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94Port 2 Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

Cold-Recycle Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

Chapter 8 Output Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97Intended Valve Position. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

Valve Flow Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98Actuator Control Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

Valve Dead Band Compensation. . . . . . . . . . . . . . . . . . . . . . . . . . .99Output Clamps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

Remote Low Output Clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . .100Tight Shut Off Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101Output Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101Output Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

Chapter 9 States and Transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103Operating State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

Operating State Request Signals . . . . . . . . . . . . . . . . . . . . . . . . .103Startup Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104Shutdown Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104Stop State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

Valve Sharing Shutdowns . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104Manual Override . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Alternate Parameter Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106Redundant Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

Switching Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

Appendix A Configuration Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

Appendix B Controller Test Sequences. . . . . . . . . . . . . . . . . . . . . . . . . . . . .139

Appendix F Application Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151

Appendix FS fA Mode Supplement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193

Glossary/Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .213

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9

List of FiguresFigure 1-1 Dynamic compressors have at least two control elements . . . . . . . . 15Figure 1-2 Basic compressor control system . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Figure 1-3 Multi-section compressor with shared recycle valve . . . . . . . . . . . . . 16Figure 1-4 Multi-section compressor with sidestreams . . . . . . . . . . . . . . . . . . . . 16Figure 1-5 Simplified P&ID for compressors operating in series . . . . . . . . . . . . . 17Figure 1-6 Simplified P&ID for compressors operating in parallel . . . . . . . . . . . . 18Figure 1-7 Antisurge Controller functional diagram . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 3-1 Analog input signal processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Figure 3-2 Communication with other controllers . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 4-1 Using dual flow transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Figure 4-2 Compensating ∆Po for a suction control valve . . . . . . . . . . . . . . . . . . 56

Figure 5-1 Defining the minimum safe flow as a function of head. . . . . . . . . . . . 64Figure 5-2 Proximity to surge for a fixed-geometry compressor . . . . . . . . . . . . . 65Figure 5-3 Proximity to surge for a variable-geometry compressor. . . . . . . . . . . 66

Figure 6-1 Typical control lines for antisurge control responses . . . . . . . . . . . . . 71Figure 6-2 Dead-zone error (e) as a function of the DEViation . . . . . . . . . . . . . . 78Figure 6-3 Typical Recycle Trip response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Figure 7-1 Imaginary orifice coefficients and equivalent flow measurements . . . 85Figure 7-2 Calculating equivalent flows when suction flow is measured. . . . . . . 88Figure 7-3 Calculating equivalent flows when discharge flow is measured. . . . . 90Figure 7-4 Setting Primary Capacity Control Thresholds . . . . . . . . . . . . . . . . . . 92

Figure 8-1 Output transformations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97Figure 8-2 Valve flow characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Figure 8-3 Valve dead band compensation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

List of TablesTable 2-1 Operating states. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Table 3-1 Available symbols for measured variable labels . . . . . . . . . . . . . . . . 41Table 3-2 Functions for OUT2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Table 3-3 Discrete input functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Table 3-4 Discrete output functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Table 4-1 Available calculated variable readouts. . . . . . . . . . . . . . . . . . . . . . . . 60

Table F-1 Analog inputs required by each fA Mode . . . . . . . . . . . . . . . . . . . . . 151

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10

Contents

Symbols and AcronymsMany of the terms and phrases represented by the following symbols and acronyms are defined in the Glossary/Index (see page 213):

α guide vane angle

ηp polytropic efficiency

σ polytropic head exponent

a mechanical power loss

A series load-sharing domain selection variable

ACR Antisurge Control Response

ACS Actuator Control Signal

AD1 to AD8 Analog-to-Digital variables

b width coefficient for margin of safety, sometimes called Total b

CCC Compressor Controls Corporation

CH1 to CH8 analog input CHannels

CPU Central Processing Unit

CR1 to CR5 Control Relays (discrete outputs)

CRD Derivative Control Response

CRI accumulated Integral Control Response

∆CRI Integral Control Response

CRLD Loop-Decoupling Control Response

CRP Proportional Control Response

CRPC Primary Capacity Control Response

CRRT Recycle Trip Control Response

CRSO Safety On Control Response

CRC Cyclic Redundancy Checksum

CRIC Cold-Recycle (flow) Indicating Controller

CV Control Variable or Check Valve

D1 to D7 Discrete Inputs

DCS Distributed Control System

dev distance between operating point and specified control line

DEV distance between operating point and surge control line

DEV' parallel compressor load-balancing variable

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11

devRT distance between operating point and Recycle Trip control line

devSL distance between operating point and surge limit line

devSO distance between operating point and Safety On control line

devTS distance between operating point and Tight Shutoff control line

DO1 to DO5 Discrete Outputs (control relays)

DPT Differential Pressure Transmitter

e error (control loop deviation)

EEPROM Electrically Erasable Programmable Read-Only Memory

ESD Emergency ShutDown

fA Application Function

FIC Flow Indicating Controller

FIOM Field Input/Output Module

FT Flow Transmitter

FY Flow Transducer

GTIC Gas Turbine (fuel) Indicating Controller

Hp polytropic Head

hr reduced polytropic head

I/O Input and Output circuits

I/P Current-to-Pneumatic signal converter

IRF Intended Recycle Flow

IT Current Transmitter

IVP Intended Valve Position

jr reduced power consumption

J power consumption

k isentropic exponent

L series compressor load-balancing variable

LD Loop Decoupling

LED Light Emitting Diode

LSIC Load-Sharing Indicating Controller (slave Performance Controller)

M Molecular weight, occasionally Motor

N rotational speed (generally, the Number of revolutions per unit time)

Ne equivalent speed

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12

Contents

Ne,s equivalent speed relative to suction temperature

NO/NC Normally-Open/Normally-Closed

OP Operating Point

OutF Output Failure

OUT1 and OUT2 analog OUTputs

P Pressure

Pac Aftercooler Pressure

Pc Compensating Pressure for mass flows

∆Pc Pressure rise across a Compressor

Pd Discharge Pressure

Pdh Discharge Header Pressure

Pfe Pressure at the flow measuring element

∆Po Pressure drop across an Orifice plate (flow measurement)

∆Po,ac Flow measurement downstream from an aftercooler

∆Po,c Calculated flow measurement

∆Po,d Discharge flow measurement

∆Po,r Reported flow measurement

∆Po,s Suction flow measurement

∆Po,ss Sidestream flow measurement

Ps Suction Pressure

Pss SideStream Pressure

PCB Printed Circuit Board

PI Proportional-Integral

PIC Pressure Indicating Controller

PID Proportional-Integral-Derivative

P&ID Piping and Instrumentation Diagram

POC Performance Override Control

psi pounds per square inch

PT Pressure Transmitter

PV1 to PV8 Process Variables

Q volumetric flow

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Series 3 Plus Antisurge Controller 13

Qd volumetric flow in discharge

qr reduced volumetric flow

qr,d reduced volumetric flow in discharge

qr,s reduced volumetric flow in suction

Qs volumetric flow in Suction

R universal gas law constant

RAM Random Access Memory

Rc Compression Ratio

Rt Temperature Ratio

RCS Redundant Control Selector

rpm revolutions per minute

RT Recycle Trip®

RTL Recycle Trip Line

RTM Recycle Trip Margin

S proximity to the surge control line (1 - DEV)

Ss Slope of the operating point line relative to the surge limit line, repre-sents proximity to surge limit

SCL Surge Control Line

SCM Surge Control Margin

SCS Station Control Signal

SL Surge Limit

SLL Surge Limit Line

SM Safety Margin

SO Safety On®

SOL Safety On Line

SOM Safety On Margin

ST Speed Transmitter

STIC Steam Turbine (speed) Indicating Controller

SV1 to SV8 Signal Variables

T Temperature

Tac AfterCooler Temperature

Tc Compensating Temperature for mass flows

Td Discharge Temperature

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14 Contents

Ts Suction Temperature

Tss SideStream Temperature

TIC Temperature Indicating Controller

TSL Tight Shutoff Line

TSM Tight Shutoff Margin

TT Temperature Transmitter

TTC Total Train Control™

U4, U5 User-defined argument variables for control line (f4) and general (f5) characterizing functions

UIC Antisurge Controller (User-defined multi-variable Indicating Controller)

UsrQ net mass flow rate

V Voltage

Vac alternating-current Voltage

Vdc direct-current Voltage

W mass flow rate, also Watt

Wr recycle mass flow rate

X, Y generic coordinates for a compressor map, also the argument and result of a characterizing function [Y = f(X)]

Z compressibility, also linear (Z-axis) position

ZT position Transmitter

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Chapter 1 OverviewThis chapter summarizes this controller’s applications and features.

Figure 1-1 Dynamic compressors have at least two control elements

Applications As shown in Figure 1-1, a centrifugal or axial compressor requires at least two control loops, one to regulate its through flow and one to regulate its antisurge (recycle or blow-off) flow.

Figure 1-2 Basic compressor control system

In a single-section compressor application, an Antisurge Controller can be combined with a Performance Controller to provide precise capacity control with minimum recycle or blowoff whether the speed, geometry (guide vane angle), gas composition, and inlet conditions are fixed or variable. In the example shown above (Figure 1-2), the Performance Controller regulates a constant speed compressor’s discharge pressure by positioning a throttle valve in the suction line,

Discharge

Suction Suction

Blo

wof

f

Recycle

Discharge

PIC — Performance ControllerUIC — Antisurge Controller

UIC

PT

FYPIC

FY FT TT PTPT TT

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16 Chapter 1: Overview

Figure 1-3 Multi-section compressor with shared recycle valve

while the Antisurge Controller opens the recycle valve just enough to prevent surge.

To adequately protect a multisection compressor, especially one that has sidestreams, each section should be protected by its own controller. Series 3 Plus Antisurge Controllers can protect such a machine even when it has only one recycle or blowoff valve (see Figure 1-3) or the flow through some sections cannot be directly measured (see Figure 1-4).

Figure 1-4 Multi-section compressor with sidestreams

UIC1 — Valve-Sharing Master Antisurge ControllerUIC2 — Valve-Sharing Companion Antisurge Controller

PTFT PT

UICPort 1FY

PTFT PT

UIC1 2

PT

Port 1 Port 1

PT

UIC2

FT FT PTPTFT

UIC1

UIC3

FYFYFY

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Figure 1-5 Simplified P&ID for compressors operating in series

When several compressors are connected in series or in parallel to achieve a higher flow rate or compression ratio, networks of Anti-surge and Performance Controllers can distribute the total load and prevent surge with a minimum of recycling. In such systems (see Figure 1-5 and Figure 1-6), each compressor or compressor section is equipped with a dedicated Antisurge Controller. In a parallel load-sharing application, Antisurge Controllers can also be used to regu-late the flow through a cold recycle loop.

In all of these applications, Antisurge Controllers can also provide limiting control of their maximum discharge and minimum suction pressures. If a recycle valve would also be the best control element for another limiting variable, a Performance Controller can serve as an auxiliary limiting control loop for an Antisurge Controller.

Port 2

LSIC UICPort 1

PTTT TT

PT PT

FT

PICFY

FT

LSIC

Port 2

UICPort 1

TT TT

PT PT

FYSIC

FY

Port 1

FY

Port 1SIC

LSIC —SIC —

Load-Sharing ControllerSpeed Controller

PIC —UIC —

Station Pressure ControllerAntisurge Controller

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Figure 1-6 Simplified P&ID for compressors operating in parallel

Port 1

TT TTPT

Port 2

LSIC FY

TIC —UIC —

Temperature ControllerAntisurge ControllerPIC —

SIC —

Station Pressure Controller

Fuel ControllerCRIC —LSIC —

Cold Recycle ControllerLoad-Sharing Controller

FY PTFT

Hot Recycle

SIC

FY

TT TTPT

FY

FY PTFT

Hot Recycle

FY

PT

Cold Recycle

FY

UIC

PIC CRIC

FY

TT

TICPort 1

UICSIC LSIC

Port 1

Port 2

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Major Features This software revision (756-004) offers the following features:

• Proximity to Surge Calculations that are invariant to changing process conditions

• Fallback Strategies that can provide continued protection when the analog and serial communication inputs required by the cho-sen proximity-to-surge calculation fail

• Closed- and open-loop Control Responses that collectively pro-tect against surge-induced compressor damage and process upsets without sacrificing energy efficiency or system capacity

• Limiting Control features that can increase the recycle or blowoff rate as needed to maintain minimum suction and maximum discharge pressures and to help regulate a Performance Con-troller’s capacity or performance override control variable

• Loop Decoupling that minimizes adverse interactions between a compressor’s capacity and antisurge control loops

• Valve Sharing and Equivalent Flow Calculations for multisection or series compressor applications

• Load Sharing for compressors operating in series or in parallel

• Operating States that protect the compressor while it is running or stopped and during startups and shutdowns

• Automatic or Manual Operation from the Front Panel or a host computer or control system

• Redundant Controller Tracking that allows one Antisurge Con-troller to serve as an on-line backup to another

• Basic or Extended I/O Hardware Configurations

• Analog and Discrete I/O ports that can be assigned functions appropriate to each application

• Control Valve Features that adapt the analog output to virtually any recycle valve, allow either that signal or its low clamp to track an analog input, and test its accuracy

• Serial Communication with companion Series 3 Plus Control-lers, operator workstations, and Modbus host systems

• Configuration and Tuning from either the Engineering Panel (from which three alternate parameter sets can be stored and recalled) or from a computer workstation

Please refer to the Series 3 Plus Antisurge Controller Revision His-tory [DS301/V] for information about previous revisions.

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Figure 1-7 Antisurge Controller functional diagram

Parallel ACSs

Recycle Balancing

SP3

ACR (IRF)

PI Algorithm

Dead Zone

e1e2

DEV

1 – S S dS s /dt

Application Function

S

s

n · b 2

b

3

· Td

0

· dS

s

/dt

· f

4

(X)

Output Reverse

Valve Flow

or

Output Clamps

Valve Dead BandCompensation

Characterizer

Tight Shut Off

ACS

IVP

OUT Readout

Output Tracking

Manual

Analog Inputs

Calculated and

Valve-Sharingand Performance Override PIs

Safety On

e

3

P

d

SP2

P

s

b

1

b

Recycle Trip

Surge Detector(fA Mode)

Response

Process Variables

DerivativeResponse

Primary CapacityControl

Control Signal

Station Controller

Valve-Sharing

RTs

Interacting

PIDs & RTs

Loop Decoupling

Remote LowOutput Clamp

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Proximity toSurge

Calculations

In order to prevent surge with a minimum of recycling, a controller must accurately determine how close the compressor is operating to its surge limit. But that distance is not something that can be directly measured. Instead, it is a function of compression ratio, flow rate, rotational speed, guide vane angle, and gas pressure, temperature, and composition.

The Antisurge Controller can use a variety of functions to calculate proximity to surge, each of which embodies a different set of simpli-fying assumptions to define a coordinate system in which the surge limit is invariant to process changes (see Calculated Variables on page 51, Application Function on page 63, and Appendix F).

FallbackStrategies

The Antisurge Controller also offers numerous fallback strategies for calculating proximity to surge when analog input or serial port fail-ures preclude using the selected fA mode. This enables it to provide continued compressor protection until the failed inputs can be restored (see Fallback Strategies on page 67).

ControlResponses

The Antisurge Controller employs a unique combination of control responses that can prevent surge without needlessly upsetting your process or requiring a large, energy-wasting surge control margin:

• A proportional-integral response protects the compressor from small, slow disturbances when it is moving toward surge and closes the antisurge valve when the machine is moving away from its surge limit (see Antisurge PI Response on page 79).

• Fast disturbances are countered by temporarily raising the surge control margin when the compressor is moving rapidly toward its surge limit, which will increase the recycle rate only when operat-ing close to that limit (see Derivative Response on page 74).

• If the combined PI and derivative responses fail to maintain an adequate margin of safety, an open-loop response ratchets the control valve open to provide the rapid increase in flow needed to prevent surge (see Recycle Trip Response on page 80).

• Finally, if unanticipated circumstances do produce a surge, the surge control margin is permanently increased, which quickly stops the surging and prevents its reoccurrence (see Safety On Response on page 75).

Limiting Control

The recycle rate can be increased as needed to limit the discharge and suction pressures (see Pressure Limiting on page 82). If there are other process constraints that can be satisfied by opening the antisurge valve, additional limiting loops can be implemented using companion Performance Controllers (see Auxiliary Limiting on page 83 and Performance Override on page 83).

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22

Chapter 1: Overview

Loop Decoupling The controller can counter the potentially destabilizing effects that can result from interactions between the various control loops regu-lating a single compressor by adjusting its control signal in response to changes in the control responses of companion controllers (see Loop Decoupling on page 83).

Valve Sharing When a multisection compressor (or group of compressors operat-ing in series) has only one recycle or blowoff valve, you should still install a dedicated Antisurge Controller for each section. The con-troller that actually manipulates the recycle valve can then keep it open enough to protect whichever section is closest to its surge limit (see Valve Sharing on page 91).

Equivalent FlowCalculations

When the flow through one section of a compressor (or group of compressors operating in series) cannot be measured, its Antisurge Controller can calculate proximity to surge by combining a side-stream or recycle flow measurement with the flow reported by a companion controller protecting an adjacent compressor section (see Equivalent Flow Measurements on page 85).

Load Sharing Networks of Performance and Antisurge Controllers can be used to regulate and protect a group of compressors operating in series or in parallel. Such control systems:

• vary the compressors’ performance and recycle rates as needed to regulate the Station Controller’s capacity control vari-able (see Primary Capacity Control on page 92);

• raise the recycle rates to limit the station performance override variable (see Performance Override on page 83); and

• prevent any compressor from recycling until all are operating at their surge limits, and balance their loads when operating at a distance from those limits (see Load Balancing on page 93).

For parallel compressor systems, the Antisurge Controllers can also equalize the recycle rates (see Recycle Balancing on page 94) and a dedicated Antisurge Controller can regulate the flow through a common recycle cooler (see Cold-Recycle Control on page 95).

Operating States Compressor startups and shutdowns are sequenced primarily by the Performance Controller. The Antisurge Controller participates by holding its control valve in a position that minimizes the risk of surge (see Operating State on page 103):

• The compressor’s status can be monitored via flow, pressure, and/or speed inputs or by a companion controller.

• When a shutdown is initiated or detected, the Antisurge Control-ler can either ramp the recycle valve open or open it as quickly

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as possible. It will then hold that valve fully open as long as the compressor is stopped, in order to minimize the possibility of back flow and reverse rotation. It can also fully close the recycle valve so purge gas can be forced through the compressor.

• When a startup is initiated or detected, the Antisurge Control-ler’s normal operation will slowly close its control valve to a position that minimizes recycle flow as efficiently as possible.

Automatic orManual Operation

Because the Antisurge Controller is an automatic protective device, its operation requires little (if any) operator intervention. However, both its status and your process can be monitored using various Front Panel, computer control, and input/output features (see Con-tinuous Operation on page 26). In addition, the recycle valve position can be directly controlled from the Front Panel or by a Mod-bus host (see Manual Operation on page 32).

RedundantController

Tracking

Dual redundancy (that is, one-to-one fault tolerance) is a standard feature of most Series 3 Plus Controllers. This means you can install one Antisurge Controller as an on-line “hot” backup to another, ready to take over instantly if the first should fail.

In a typical application (see Redundant Control on page 36), the two controllers are interconnected via a Redundant Control Selector (RCS) that connects the control element to the primary controller. The backup controller then tracks (that is, monitors and duplicates) the operating state and control response of the primary controller via the Port 1 serial communications link. If that controller’s fault relay de-energizes, the system bumplessly transfers control of your pro-cess to the back-up unit.

HardwareConfigurations

The Antisurge Controller can use either of two compressor controller configurations (see Hardware Options on page 37). The basic con-figuration provides back-panel terminals for its I/O circuits, while the extended I/O option uses external wiring modules.

Analog andDiscrete I/O

Each of the eight analog inputs (see Analog Inputs on page 38) is tested by comparing it to individually-defined alarm limits. Although the inputs for most features are fixed, some can use any appropriate or otherwise unused channels.

Analog OUT1 is usually used to position a recycle or blow-off valve, while OUT2 can drive a remote display for a user-selected variable (see Analog Outputs on page 42).

One or two of the five control relays can be set up to signal hard-ware and self-test failures, the others can be assigned a variety of controller and process conditions (see Discrete Outputs on page 45 and Fault Relays on page 45). In contrast, the functions of the seven

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discrete inputs (see Discrete Inputs on page 44) are predefined and cannot be changed.

Control ValveFeatures

The actuator control signal can be clamped, adapted to a direct or reverse, linear, quick-opening, or equal-percentage valve, and compensated for a deadband or low-flow leakage (see Output Vari-ables on page 97). The controller can also detect an excessive deviation of the actuator control signal from its intended value (see Output Loopback Test on page 42) or of the recycle valve from its intended position (see Valve Position Test on page 43).

The Antisurge Controller also offers low and absolute signal select algorithms for sharing control of the recycle valve with another device (see Remote Low Output Clamp on page 100 and Output Tracking on page 102).

SerialCommunication

All Series 3 Plus Controllers have four Serial Ports (see page 48):

• Ports 1 and 2 are used to coordinate their actions with other CCC controllers (see Limiting Control, Loop Decoupling, Equiv-alent Flow Calculations, Valve Sharing, Load Sharing, Operating States, and Redundant Controller Tracking).

• Ports 3 and 4 are used for computer communication and control (see Continuous Operation on page 26 and the Series 3 Plus Antisurge Controller Modbus Data Sheet [DS301/M]) using Modbus RTU commands. This allows a host control system or a computer running controller support software (such as our COMMAND system) to monitor or even control the operation of your compressor. Some of our support programs can also change the configuration and tuning of the controller.

Configuration andTuning

Each Antisurge Controller is adapted to its specific application by assigning values to its configuration and tuning parameters (see Appendix A). This can be done from the Engineering Panel or a computer running one of our configuration programs.

If your application requires routine changes to a controller’s configu-ration or tuning, up to three sets of alternate parameter values can be stored. Engineering Panel procedures are provided for defining these alternate sets, determining which one is in use, and switching to a different one (see Alternate Parameter Sets on page 106).

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Chapter 2 OperationThis chapter describes the operation of the Antisurge Controller.

OperatorInterfaces

This section summarizes the features that can be operated via the controller’s front-panel, remote control, and Modbus interfaces.

The front-panel keys, LEDs, and readouts can be used to select automatic or manual operation, monitor its antisurge and limiting control loops, display and clear the surge count, and display various internal and process variables, as described in the Series 3 Plus Antisurge Controller Operator Interface Description [DS301/O].

The controller’s remote control inputs and outputs are primarily for integration with other devices, although they could also be used to implement a limited remote control panel. Discrete Inputs (see page 44) can be used to select the operating state, to trigger output track-ing, or to clear the surge count. Discrete Outputs (see page 45) can be connected to external alarms and indicators for various operating conditions. Process variable Analog Inputs (see page 38) can be monitored directly, while some internal variables can be monitored via Analog Outputs (see page 42).

The Modbus interface can be used to select automatic or manual operation, monitor the antisurge and limiting control loops, monitor and clear the surge count, change a limited number of configuration parameters, and monitor various internal and process variables, as described in the Series 3 Plus Antisurge Controller Modbus Data Sheet [DS301/M].

Note: Because all three interfaces are always active, the compressor can be monitored and controlled using any combination of their features.

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26 Chapter 2: Operation

ContinuousOperation

When operating automatically in its Run state, the controller varies the Valve Position to satisfy its Surge Protection, Pressure Limiting, Performance Limiting, and Load Sharing objectives. Because little intervention is needed, the Operator Interfaces serve primarily as a means of monitoring its operation (and that of the compressor).

This state is selected whenever specified inputs (usually speed, flow, and pressure) indicate the unit is running, the controller’s own D2 and D6 inputs are cleared, and a companion controller (if one is designated) is also operating in its Run state. The AUXiliary readout will then display the operating state as “Status RUN” and any Run relays and the Modbus Run discrete bit will be set.

Valve Position The position of the recycle valve can be monitored via the OUT readout, Modbus Displayed OUT register, or analog output OUT1. The Modbus High Clamp or Low Clamp discrete bit will be set if the control response equals the corresponding clamp, and any Valve Open relays will be set if that response exceeds its low clamp. If an analog Remote Low Output Clamp (see page 100) has been set up, the Tracking LED will flash whenever that input exceeds the low clamp parameter, regardless of the control response value.

Valve Sharing A group of Antisurge Controllers protecting the same multi-section compressor can use serial communications to share a single recycle or blow-off valve (see Valve Sharing on page 91). The controller that directly manipulates that valve is then referred to as the valve-shar-ing master, while the rest are called valve-sharing companions.

The OUT readout of a valve-sharing companion is always blank, and its actuator control signal (ACS) cannot be manipulated manu-ally or by a Modbus host. However, its Modbus Displayed OUT input register will track the master controller’s ACS.

This feature can also be applied to compressors that operate in series with a common recycle or blow-off valve. In that case, some of their compressors might be loaded while others are stopped or idled. The master will modulate that valve as required to protect the compressors whose controllers are operating in the Run state. If its own compressor is unloaded but one or more others are not, it will operate in the Run state but will display it as “Status OFF”.

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Surge Protection The DEViation between the compressor’s operating point and the controller’s surge control line (SCL, see Chapter 5) can be moni-tored via the DEV readout, DEViation register, or analog OUT2:

• If DEV is at or near zero, the compressor is operating close to or on its SCL. If a non-zero Dead Zone (see page 78) has been defined, OUT should remain steady. Otherwise, it will vary as needed to keep the operating point exactly on that line.

• When DEV is positive, the compressor is operating to the right of its SCL. If the recycle valve is not fully closed, the Antisurge PI Response (see page 79) will gradually close it.

• If DEV becomes negative, the compressor is operating to the left of the SCL, where the distance between the operating point and surge limit is less than desired. As long as it does not get too close to the actual surge limit, the controller will rely on its PI algorithm to raise the margin of safety back to the desired level.

The distance between the SCL and the actual surge limit depends on the rate at which the compressor is approaching its surge limit (see Derivative Response on page 74) and the number of times it has surged (see Safety On Response on page 75). It can be dis-played on the front-panel AUX readout by pressing the SCROLL key to scroll from the STATUS display to the “Total B= ##.#” variable, where ##.# is the distance between the SCL and SLL in percent.

The controller’s analog inputs can be monitored via the front-panel AUXiliary readout Measured Variables menu or Modbus Channel # registers. Additional process conditions calculated by the selected proximity-to-surge algorithm can be monitored via the Calculated Variables menu and various Modbus registers (for example, the Pressure Ratio, Temperature Ratio, and Sigma).

A continuing or sudden drop in the DEViation will trigger the Recycle Trip Response (see page 80). The yellow RT LED will then light and any RT relays and the Modbus Recycle Trip discrete bit will be set while the controller ratchets open the antisurge valve. Once a mini-mum safe DEViation is restored, the RT relays and discrete will be cleared, the RT LED will go out (after a fixed delay), and the RT response will decay to zero.

If for some reason the compressor actually goes into surge, the con-troller will detect the characteristic rapid fluctuations of head and/or flow and trigger its Safety On Response (see page 75). The red SO indicator will then light and any SO relays and the Modbus Safety

Note:

A Recycle Trip action should not be viewed as a cause for alarm, it simply means the compressor is operating close enough to its surge limit to justify aggressively increasing the recycle rate. By allowing your compressor to safely operate that close to its surge limit, this feature actually saves you money by reducing recycling costs.

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On discrete and coil bits will be set to indicate the surge control mar-gin has been increased to prevent additional surges from occurring.

Each detected surge increments the cumulative and event Surge Counters (see page 76) and triggers a further increase in the surge control margin. The cumulative count can be displayed in the ALT readout by pressing DISPLAY SURGE COUNT, and can also be monitored via the Surge Count register. Any Surge Event relays are set if the event count reaches a user-defined threshold within a specified period of time (if not, that count is automatically reset).

If a Safety On condition is indicated, you should determine why that response was tripped and whether or not the controller needs to be reconfigured to provide a larger, permanent margin of safety. Once that determination and any needed reconfiguration are completed, you can reset the surge counts to zero and restore the initial surge control margin by pressing the RESET SAFETY ON key, asserting discrete input D5, or clearing the Modbus Safety On coil.

In a system with multiple control elements, the actions of any con-troller can affect the control variables of the others. To minimize such destabilizing loop interactions, Antisurge Controllers monitor changes in the control responses of specified companions and adjust their own output signals to keep their compressors operating at the same distance from surge.

Warning! Do not reset the Safety On response until the cause of any surging has been determined and corrected.

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Pressure Limiting If either the discharge pressure is too high or its suction pressure is too low (or both), and any Limit relays and the Modbus Limit discrete bit will be set. The controller will then increase the recycle rate (see Pressure Limiting on page 82), which should raise the suction and lower the discharge pressure. The yellow Limit LED will light if the limiting loop opens the recycle valve faster than the surge protection features otherwise would.

If you press the DISPLAY LIMIT key, the AUX readout will identify the out-of-range pressure, the DEV readout will display its value, and the ALT readout will display its set point. You can also monitor those pressures via the corresponding Modbus Channel # registers, while the parameters that define their set points can be monitored and even changed via the Pd Limit and Ps Limit holding registers.

PerformanceLimiting

An Antisurge Controller can be configured to help a companion Per-formance Controller counter excessive deviations of its performance override control variable by increasing the recycle or blow-off flow (see Performance Override in Chapter 6). At such times, the front-panel ALT readout displays the “POC” acronym and the Modbus POC Active discrete bit is set.

Load Sharing In a Series 3 Plus Control System for multiple compressors operat-ing in series or in parallel, a Station (master Performance) Controller regulates a header pressure or flow by indirectly manipulating the throttle and antisurge control elements of the individual compres-sors (as described in the Station Controller section in Chapter 2 of IM302). In such a system, each Antisurge Controller will increase the recycle rate of its compressor (which will reduce the discharge header pressure and flow) when its operating point is already near or on its surge control line and less throughput is needed (which would move the compressor even closer to surge). Under any other conditions, changes in the compressor network’s throughput are achieved by manipulating the control elements of the Load-Sharing Performance Controllers.

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SequencingOperation

The loading and unloading of a compressor is sequenced primarily by its Performance Controller (see Chapter 2 of IM302). Startups and shutdowns are usually sequenced by the controller for the com-pressor’s driver. Provided neither output nor redundant controller tracking is active (see Tracking States), an Antisurge Controller will participate mainly by selecting an appropriate operating state (see Table 2-1):

• While its machine is loaded, an Antisurge Controller operates in its Run state (see Continuous Operation), which modulates the recycle valve to prevent surge with minimal recycling.

• When a Shutdown is initiated, the recycle valve is either ramped open or opened as fast as possible.

• While its machine is stopped or idling, an Antisurge Controller operates its Stop State, which holds the recycle valve fully open.

• If the purge input is then asserted, the controller selects its Purge State, which holds the recycle valve fully closed.

• When a Startup is initiated, the controller simply selects its Run state. Its PI loop will then slowly close the recycle valve.

Shutdown An Antisurge Controller can be set up to open the recycle valve to its high clamp position (see Operating State on page 103) when the compressor is idled or shut down:

• An emergency shutdown immediately opens that valve.

• A normal shutdown usually ramps it open, although it can be configured to open it immediately and will always do so if the operating point moves to the left of the RTL.

Table 2-1 Operating states

Name Display Description

RunRUN

The compressor is loaded and the control response is being varied to prevent surge.

OFFThis compressor section is unloaded but the valve is being modulated to protect another.

StopSTOP

A normal shutdown was or is being used to idle or shut down the compressor.

ESDAn emergency shutdown was used to idle or shut down the compressor.

Purge PURGEThe compressor is unloaded but the recycle valve is fully closed.

Track TRACKActuator control signal is tracking the output of another device or controller.

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In either case, any Run relays and the Modbus Run discrete are immediately cleared, the operating state display changes to “Status STOP” or “Status ESD”, and the Surge Counters (see page 76) are reset to zero (if so configured).

An ESD can be triggered only by this controller’s own D2 discrete input. A normal shutdown can be triggered by its own D6 discrete input, by the stop or shutdown sequence of a companion controller, or by a process condition that indicates the compressor is being stopped or idled (abnormally low flow, head, or rotational speed).

Stop State While its compressor is stopped or idling, an Antisurge Controller will operate in its Stop state with all Run indicators cleared. It then holds the recycle valve fully open:

• If the compressor is idling, this minimizes the drive power and risk of surge. The displayed DEViation should show a positive value perhaps as great as “.A24” (1.024).

• If the compressor is stopped, this minimizes any reverse flow or rotation that might occur if the discharge check valve leaks. The DEViation display will be unpredictable and perhaps erratic, but can be safely ignored (a stopped compressor cannot surge).

The operating status will display as STOP or ESD, depending on how this state was selected. Manual Operation can be initiated only if its selection while operating in this state is enabled.

Purge State If the controller is operating in its Stop state, asserting either its own D3 discrete input or that of a designated companion controller will select the Purge state. This sets the actuator control signal to zero (100 percent for a signal-to-close valve), thus completely closing the recycle valve. Purge gas can then be forced through the compres-sor instead of bypassing it through the recycle line. The AUXilliary readout will display this operating state as “Status PURGE”.

Startup An Antisurge Controller operating in its Stop state will automatically switch to the Run state if its D2 and D6 discrete inputs are cleared, the designated companion controller (if any) selects its Run state or initiates its startup sequence, and the head, flow, and speed exceed user-defined minimums (thus indicating the compressor is running).

This immediately sets any Run relays and the Modbus Run discrete bit and changes the operating state display to “Status RUN”. The PI response will then gradually reduce the recycle flow as far as surge protection and process limiting conditions permit.

Warning! Requesting the Purge state while the compressor is idling not only leaves the unit unprotected but might even trigger a surge.

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ManualOperation

When manual operation is selected, momentarily pressing the Raise or Lower key will change the actuator control signal by 0.1 percent, holding either down changes it at a steadily increasing rate. The resulting value can be monitored via the OUT readout, an analog output assigned the Out function, or the Displayed OUT input regis-ter. Alternately, the control signal can be set directly by writing to the Actuator CS holding register.

Although the Output Clamps (see page 100) do not apply in manual, the Remote Low Output Clamp (see page 100) does. Thus, you can raise the control signal above the high or reduce it below the low clamp parameter, but cannot reduce it below an analog low clamp.

While in manual, the controller will continue to calculate and display the deviation between the operating point and the surge control limit, so you can tell if you are moving the compressor too close to surge by watching the DEV readout. If you inadvertently move the operating point to the left of the Recycle Trip line, the RT LED lights and the controller reverts to automatic operation. It will then remain in automatic even after an adequate safety margin is restored.

The controller will also continue to monitor its operating state inputs and the AUXiliary readout will continue to display the selected state (for example, “Status RUN”). If those inputs dictate a transfer out of the Run state, the controller will revert to automatic. However, you can then switch back to manual by pressing the AUTO/MAN key, provided manual operation in the newly selected state is enabled.

Although Pressure Limiting is suspended during manual operation, the Limit LED and any Limit relays will continue to indicate whether or not the suction and discharge pressures are within their respec-tive limits, and you can still use the DISPLAY LIMIT key to display these control variables and their set points.

Initiating Manual Manual operation can be selected at any time unless the controller is operating in its Stop or Purge state and manual operation in those states has not been enabled (see Manual Override). However:

• If manual operation and Output Tracking are both selected, the remote device will control the output signal.

• In a Redundant Control system, only the active controller can be manually operated (the backup will track that selection).

Manual is initiated by pressing the AUTO/MAN key or clearing the Modbus Automatic coil. The Manual LED then lights and the Auto LED, any Auto relays, and the Automatic coil and discrete bit all clear.

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RestoringAutomatic

Pressing the AUTO/MAN key while in manual or setting the Modbus Automatic coil initiates a bumpless return to automatic control. The Manual LED then clears and the Auto LED, any Auto relays, and the Automatic coil and discrete bit all set.

This action will not change the actuator control signal unless it is above its high clamp or below its low clamp, in which case it will jump back to that clamp. In addition, the Valve Dead Band Compen-sation (see page 99) feature will remember which direction the operator last moved the output while in manual and resume opera-tion accordingly.

Manual Override To prevent surge while the controller is in manual, it will revert to automatic if the operating point moves to the left of the Recycle Trip control line (RTL). However, you can enable an override of this behavior (see Manual Override on page 105), in which case the controller will remain in manual until the operator restores automatic operation (even if the compressor surges). To indicate this danger, the front-panel Man LED will flash and any relays assigned the MOR function will trip, regardless of the DEViation, whenever manual is selected while that override is enabled. If the operating point then moves to the left of the RTL, the RT LED will light and remain on until an adequate safety margin is manually restored.

If the Manual Override is enabled, the controller will also remain in manual when the operating state inputs dictate a transfer out of the Run state and manual operation can be initiated even when the Stop or Purge state is selected.

When manually operating the controller via its Modbus interface, you can determine whether or not Manual Override is enabled by reading the Manual Override coil or discrete, and can enable and disable this feature by setting and clearing that coil.

If the Manual Override is disabled (as recommended), the Manual While Stopped parameter determines whether or not manual can be initiated while the Antisurge Controller is in its Stop or Purge state.

Caution: We advise you not to permanently enable the Manual Override parameter, because it disables all surge protection while in manual.

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Fault Indicators In addition to a General Fault, which would be indicated via the Fault LED and relays, the Antisurge Controller can use front-panel LEDs, assignable relays, and Modbus discrete bits to indicate Serial Com-munication Errors, Analog Input or Transmitter Failures, Output Failures, and Valve Position Failures. It will also indicate a Fallback Condition if analog or serial failures prevent it from calculating the selected proximity-to-surge function.

General Fault Each Series 3 Plus Controller has a watchdog circuit that must be regularly reset by its control program. If it does time out, it will de-energize the fault relay and reset the CPU chip, thus causing the control program to restart:

• If that restart succeeds, it will reset the timer, clear the relay, and temporarily set the Modbus Reset discrete. The Engineer-ing Panel will beep and display “Reset”.

• If it fails, the fault relay will remain de-energized and the Front Panel will light its Fault LED (and turn the other thirteen off). This can indicate either a software error or a hardware problem that prevents the control program from running.

If the fault relay has also been assigned a second function (see Fault Relays on page 45), that condition will not light the Fault LED. If that assigned function is one that has its own LED, you can tell why the fault relay has tripped by looking at the Front Panel.

Serial CommunicationErrors

When the controller fails to detect expected serial transmissions, it will light the ComErr LED and set any Serial Communication Error (SerC) relays and the Modbus Port 1 Fail or Port 2 Fail discrete (see Serial Communication Errors on page 49).

Because the exact meaning of these conditions depends on which features have been enabled, their interpretation will be highly site specific. Loss of Port 2 communications will disrupt load-sharing and performance override control. A Port 1 serial error can also disrupt those features, as well as loop decoupling, multi-section compres-sor surge protection and valve sharing, automatic sequencing and operating state selection, and redundant control.

Analog Input orTransmitter Failures

Whenever one or more analog inputs is beyond its valid range, the controller lights its TranFail LED and sets any Transmitter Failure (Tran) relays and the Modbus Tran Fail discrete (see Transmitter Testing on page 39).

This condition usually indicates a failure in the input loop (transmit-ter, signal wire, and Analog PCB circuit), but might also be used to alarm undesirable process conditions.

Caution:The controller’s output signal is totally unpredictable when a watch-dog fault is indicated. Process disruptions or compressor damage can result if it is not immediately disconnected from your process.

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Output Failures If the controller detects a difference of more than five percent between the intended and loopback values of the control signal (see Output Loopback Test on page 42), it will set any Output Failure (OutF) relays and the corresponding Modbus DO State discrete (there is no dedicated bit nor front-panel LED for this condition).

This condition may indicate miscalibration of the input or output cir-cuitry, breaks or poor connections in the wiring between the input, output and final control element, or actual failure of the Analog PCB Assembly. It could be caused by failures in the loop-back circuitry only — the actual output signal may in fact have the intended value.

Even a genuine output signal miscalibration might not be critical. The controller’s integral action can often overcome such a discrep-ancy, provided it is constant. However, such problems can prevent the controller from fully opening or closing the final control element.

Valve Position Failures If the measured recycle valve position deviates significantly from its intended value (see Valve Position Test on page 43), the controller will set any Position Failure (PosF) relays and the corresponding Modbus DO State discrete (there is no dedicated bit nor front-panel LED for this condition).

Although this condition would be triggered by a malfunctioning valve positioner or position transmitter, it might also indicate miscali-bration or failure of the input or output circuitry, breaks or poor connections in the actuator control or position input loop, or a failure of the Analog PCB Assembly.

Fallback Condition If the controller is unable to calculate the selected proximity-to-surge function due to an analog input or serial communication failure, it will light its Fallback LED, set its Modbus Fallback discrete, and switch to a simpler function, maintain a minimum flow, or hold its output steady (see Fallback Strategies on page 67). In the latter case, the Auto LED will flash to indicate the controller is operating automati-cally but is holding its actuator control signal steady.

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Tracking States The Antisurge Controller includes two features that allow an external device to manipulate its actuator control signal (ACS):

• When Output Tracking is active, the ACS tracks an analog sig-nal from a remote device.

• When Redundant Control is active, it tracks the ACS of another Series 3 Plus Antisurge Controller.

If either feature is active, the operating state will display as “Status TRACK” and the Tracking LED will either light (redundant tracking) or flash (output tracking). Because they are triggered by discrete inputs that can be monitored directly, there are no relay functions that indicate either of these states. A Modbus host can detect them by monitoring the corresponding DI Condition discretes, and the Tracking discrete is set by redundant but not output tracking.

Output Tracking The Antisurge Controller can be set up as a signal selector for its final control element (see Output Tracking on page 102), in which case the actuator control signal is kept equal to a designated analog input signal whenever discrete input D4 is asserted.

The Auto and Manual LEDs, relays, and bits will indicate which mode the controller will return to when D4 is cleared, and you can change that selection by pressing the AUTO/MAN key or forcing the Automatic coil. In either case, the transfer will be bumpless.

RedundantControl

If one Antisurge Controller has been installed as an on-line “hot” backup to another (see Redundant Tracking on page 106), it will use serial communications to track the outputs and states of that active controller whenever its own D1 discrete input is cleared.

In a typical redundant system, each pair of Antisurge Controllers is interconnected via a Redundant Control Selector (RCS) that moni-tors their fault relays, controls their D1 inputs, and connects the valve actuator to the selected controller’s analog output. If the main controller’s fault relay de-energizes, the RCS automatically transfers control of the recycle valve to the backup controller (provided that it has not faulted as well). That controller then initiates control begin-ning from the last conditions received from the main controller.

The RCS also indicates which controller is active by lighting its green MAIN or red BACK-UP LED, and you can manually select the active controller by pressing the Switch to Back-Up or Switch to Main push-button.

Note:The RCS will not automatically return control of your process to the main controller after a fault is cleared (this must be done manually) and will never automatically or manually transfer control to a control-ler that appears to have failed.

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Chapter 3 Input/Output FeaturesThis chapter tells how to configure the analog and discrete inputs and outputs and serial communication ports.

HardwareOptions

The Antisurge Controller uses either the Basic Compressor Control-ler (BCC) or Extended Compressor Controller (ECC) hardware configuration, as described in the Components and Configurations section in Chapter 1 of IM300/H. Either provides the following input and output circuits:

• eight Analog Inputs (CH1 to CH8),

• two standard Analog Outputs (OUT1 and OUT2),

• seven Discrete Inputs (D1 to D7),

• five Discrete Outputs (CR1 to CR5), and

• four Serial Ports (Port 1 to Port 4).

When the ECC configuration is used, all I/O terminals are provided on a separately mounted Field Input/Output Module (FIOM), which is connected to an Extended I/O Back Panel by a High-Density Interconnect Cable (HDIC).

Disabling InputSignals

As an aid to developing and demonstrating Series 3 Plus Antisurge Controllers, they include a CPU Inputs Lockout [MODE:D LOCK 6] parameter that, when enabled, configures the controller to ignore its analog and discrete inputs (which can then be updated via the Port 3 or Port 4 Modbus serial link).

Note: The availability of the discontinued FIOM cannot be guaranteed.

Caution: An installed controller should not be operated with LOCK 6 enabled, as that would prevent it from receiving needed input signals.

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38 Chapter 3: Input/Output Features

Figure 3-1 Analog input signal processing

Analog Inputs Each Series 3 Plus Controller is equipped with eight analog inputs. As described in the Analog Input Installation section in Chapter 6 of IM300/H, they are set up as either 0 to 5 Vdc or 4 to 20 mA inputs by installing resistors on either the Field Input/Output Module or setting jumpers on the Analog PCB Assembly (if not using FIOMs).

In this manual, we will refer to both the input circuits and their analog signals as Channels 1 through 8 (CH1 to CH8) — the meaning in each case should be clear from its context.

The processing of these inputs and the terms used to distinguish their intermediate values are illustrated by Figure 3-1:

Step 1: The raw analog inputs are converted to equivalent digital values called Analog-to-Digital Variables (AD1 to AD8).

Step 2: Transmitter Testing compares each AD variable against its individual alarm limits.

Step 3: The AD variables are converted into percent-of-range Signal Variables (SV1 to SV8).

Step 4: Gains and biases are then applied to obtain the Process Variables (PV1 to PV8) used by the control calculations.

Step 5: The signal variables are also independently scaled to obtain the Measured Variables (MV1 to MV8) displayed by the AUXil-iary readout’s Analog In Menu.

AD (%)

PV = Bias +

SV (%)

(SV · Gain)

PV (%)MV

MV = Min +(Span · SV)

TEST 4

PV = Bias +

SV (%)

AN IN ON(e.g., 4 to 20 mA)

AN IN OFF(e.g., 0 to 10 V)

CH (V)

SV = AD

AD (%)Failed if: < AN IN LOW > AN IN HIGH

SV = 1.25 · (AD - 20%)

SamplingHardware

CH (mA)

Failed if: < AN IN LOW > AN IN HIGH

(SV · Gain)

PV (%)MV

SamplingHardware

MV = Min +(Span · SV)

TEST 4

SV (%)SV (%)

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Analog-to-DigitalVariables

The input circuitry converts the analog input signals into equivalent digital values for use by the CPU. Each signal is passed through a hardware filter to remove unwanted high frequency components, and a windowing filter that samples each signal several times per scan cycle and reports the resulting average.

Because these values are generated by an analog-to-digital con-verter, we refer to them as analog-to-digital variables (AD1 to AD8). They are reported to the CPU as percentages of the analog signal’s full-scale value. For example, a 20 mA signal would be reported as 100 percent, while 4 mA would be reported as 20 percent.

TransmitterTesting

The controller tests each analog input against a user-defined range. If any of them is outside of its range, the front-panel TranFail LED is lit, any Transmitter Failure (Tran) relays are energized and the Mod-bus Tran Fail discrete is set. You can use the Transmitter Status Test [MODE:D ANIN –] to identify the failed input.

This feature is configured by defining the Analog Input Low Alarm Limit [MODE:D ANIN # LOW] and Analog Input High Alarm Limit [MODE:D ANIN # HIGH] for each input, which are set as percent-ages of the full-scale analog-to-digital variables. For example, you would enter AN IN LOW as 15.0 percent to set the lower limit of a 4 to 20 mA signal to 3.0 mA.

Because an analog input can never be higher than 102.4 (A2.4) nor lower than 00.0, setting ANIN HIGH and LOW to these values has the effect of excluding that channel from the transmitter alarm fea-ture. Using these values for unused inputs prevents them from interfering with the proper operation of this feature.

Signal Variables Each analog-to-digital variable is then converted to a percent-of-range signal variable according to whether or not the corresponding transmitter uses an offset zero (for example, 4 to 20 mA or 1 to 5 Vdc). Signals that are so offset are scaled as:

Otherwise, the signal variable is set equal to the analog-to-digital variable (AD). In either case, the SV values are constrained to the range 00.0 to 100.0 percent. Higher values are changed to 100.0, lower values to 00.0. You can use the Signal Values Test [MODE TEST 4] to directly examine these signal variables from the Engi-neering Panel.

Any signal that has an offset zero (for example, a 4 to 20 mA input) must be identified by enabling the corresponding Offset Zero Input [MODE:D ANIN #]. Signals that are not offset are identified by dis-abling the corresponding parameter.

SV 1.25 AD 20 percent–( )⋅=

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Process Variables The analog inputs for some control calculations must be converted to absolute values. For example, the pressure measurements used to compute a compression ratio must be scaled as percentages of the highest absolute pressure either of their sensors can measure. To this end, the controller converts its signal variables into process variables by applying appropriate gains and biases:

where:

Bias = (Offset · 100) / Maximum

Gain = Range / Maximum

Maximum = absolute measurement corresponding to the highest possible transmitter signal. If there is more than one transmitter of a given type, this should be the largest such value for the group

Offset = absolute measurement corresponding to lowest possi-ble transmitter signal

PV = Process Variable, expressed as a percentage of abso-lute maximum

Range = span of the transmitter in question

The gain and bias for each process variable must be assigned to the corresponding Process Variable Gain [COND:D GAIN #] and Pro-cess Variable Bias [COND:D BIAS #]. For unused channels, set the gain to 1.000 (.A00) and the bias to 00.0.

MeasuredVariables

The AUXiliary Display’s Analog In menu is used to display the con-troller’s eight signal variables, scaled to appropriate ranges, along with descriptive labels of your choosing. For example, you might dis-play an inlet temperature signal as:

The available choices are set up by each input’s five Measured Vari-able [COND:D DISPLAY 0] parameters. For example, the DISPLAY 0 1 parameters govern the display of signal variable SV1:

• Each Measured Variable Display [COND:D DISPLAY 0 #] parameter defines whether the corresponding variable can be viewed (SV1 can be displayed only if DISPLAY 0 1 is On).

• Each Measured Variable Label [COND:D DISPLAY 0 # –] parameter defines the label that will precede the numeric value of the input. Each can be any combination of eight symbols from Table 3-1. The default labels [see page 5 of DS301/O], can be restored by entering the COND:D DISPLAY 0 0 key sequence.

PV Gain SV Bias+⋅=

TempIn: 400

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• Each signal variable’s

Measured Variable Minimum

[COND:D DISPLAY 0 # LOW] defines the digits shown when it is zero, its

Measured Variable Maximum

[COND:D DISPLAY 0 # HIGH] defines the digits shown when it is 100 percent, and its

Mea-sured Variable Decimal

[COND:D DISPLAY 0 # •] defines the decimal point position. Mathematically, this can be stated as:

where

n

SV is the signal variable’s normalized value.

Because the decimal point is a character that requires one of the four display positions, only three digits can be displayed unless that parameter is disabled (Off). In other words, that parameter identifies the digit the decimal should replace (that and all less-significant dig-its are shifted one position to the right). A value of one corresponds to the right-most, least-significant digit, while four is the left-most, most-significant digit. Thus, if DISPLAY 0 1 HIGH is 3210, the five possible values of DISPLAY 0 1 • would yield the following displays when SV1 is 100 percent:

0: 3210 1: 321. 2: 32.1 3: 3.21 4: .321

To obtain the most precise possible readouts, you should always make the DISPLAY HIGH parameters as large as possible. For example, if you want to display three digit numbers from 0 to 600, set DISPLAY HIGH to 6000 and DISPLAY • to 1 (for a trailing deci-mal). This will give more precise readouts than you would get by setting DISPLAY HIGH to 0600 and DISPLAY • to 0.

If

Auxiliary Display Reset

[MODE:D LOCK 9] is disabled, Measured Variables will be displayed until another variable is selected. Other-wise, the operating state display is restored 60 seconds after the MENU or SCROLL key was last pressed.

Table 3-1 Available symbols for measured variable labels

MV Min SVn( ) Max Min–( )⋅+[ ] 10dec⁄=

Î Í Ì ± ¥ Ò

space

! " # $

% & ' ( ) * + , - . /

0 1 2 3 4 5 6 7 8 9 : ; < = > ? @

A B C D E F G H I J K L M N O P

Q R S T U V W X Y Z [ \ ] ^ _ `

a b c d e f g h i j k l m n o p

q r s t u v w x y z

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Analog Outputs The Antisurge Controller has two standard analog outputs, both of which are generated as both 4 to 20 mA and 0 to 5 Vdc signals (although only one of these signals can be used for each output):

• Unless the control response is sent to a companion valve-shar-ing controller (see Valve Sharing on page 91), OUT1 is used to manipulate the compressor’s recycle or blowoff valve (see Actu-ator Control Signal on page 99).

• OUT 2 is generated as the equivalent of one of the variables listed in Table 3-2, as specified by the Second Output Assigned Variable [COND:D OUT 2]. It can be used to drive a readout or graphical display or be connected to a DCS analog input.

The Output Loopback Test can be used to compare the actual out-put signal to its intended value, while the Valve Position Test can be used to compare the measured and intended positions of the final control element.

Table 3-2 Functions for OUT2

Output LoopbackTest

The controller can be configured to energize one or more discrete outputs to indicate an excessive deviation between the measured and intended values of the actuator control signal.

This feature is set up by connecting OUT1 to analog input CH8, as described in the Analog Output Installation section in Chapter 6 of IM300/H. Any discrete output assigned the output failure (OutF) function would then energize if SV8 differed from the intended actu-ator control signal by more than five percent, or if the value of CH8 was outside of its Transmitter Testing range.

Code Signal

Out Actuator Control Signal (see page 99)

Flow Displayed Flow (see page 61)

S proximity to Surge Control Line (see page 72)

UsrQ Displayed Net Flow (see page 62)

September 2005 IM301 (6.1.3)


43

Valve PositionTest

The controller can also be configured to energize one or more dis-crete outputs to indicate an excessive deviation of the measured and intended positions of the final control element.

This feature is set up by connecting a valve position signal to analog input CH7:

• For a signal-to-open control element, the position signal must increase as the control element opens.

• For a signal-to-close control element, the position signal must decrease as the control element opens.

Any discrete output assigned the position failure (PosF) function would then energize if SV7 differed from the intended actuator con-trol signal by more than the Position Failure Threshold [COND:D LVL 5] for at least the Position Failure Delay [COND:D CONST 5], or if the value of CH7 was outside of its Transmitter Testing range.

September 2005 IM301 (6.1.3)


Discrete Inputs All Series 3 Plus Antisurge Controllers are equipped with seven discrete inputs (D1 to D7) that can be used to trigger the control fea-tures listed in Table 3-3. The threshold level above or below which these inputs are asserted or cleared is listed on the Series 3 Plus Compressor Controllers Hardware Specifications [DS300/H]:

ESD Setting D2 will trigger an emergency shutdown, provided that fea-ture is enabled (see Operating State Request Signals on page 103).

Output Tracking Setting D4 will cause the actuator control signal to track a specified analog input, provided that feature is enabled (see Output Tracking on page 102).

Purge Setting D3 will fully close the recycle valve, provided that feature is enabled and the controller is operating in its Stop state (see Operat-ing State Request Signals on page 103).

Recall Setting D7 will recall the second alternate parameter set and clear-ing it will recall the first, provided that feature is enabled (see Alternate Parameter Sets on page 106).

Reset SO Setting D5 will reset the Cumulative Surge Count to zero (see Surge Counters on page 76).

Stop Setting D6 will select the Stop state and clearing it will select the Run state, provided that feature is enabled (see Operating State Request Signals on page 103).

Tracking Setting D1 will cause this controller to track the operation of a com-panion Antisurge Controller, provided that feature is enabled (see Redundant Control on page 36).

The states of these inputs can be displayed on the front-panel AUX readout by pressing the SCROLL key while the operating STATUS is displayed. “DGI= 1234567” is then displayed, where each digit appears only if that discrete input is set.

Table 3-3 Discrete input functions

Input Function

D1 Redundant Tracking request

D2 Emergency Shutdown (ESD) request

D3 Purge request

D4 Output Tracking request

D5 Reset SO (Safety On) request

D6 Normal Shutdown (Stop) request

D7 Recall alternate parameter set

September 2005 IM301 (6.1.3)


DiscreteOutputs

The controller’s discrete outputs can be used to automatically trigger alternate control measures or to control External Alarms for a variety of process and controller conditions.

The operation of each relay is set by selecting one of the conditions from Table 3-4 as its Relay Assigned Function [MODE:D RA #]. Except for the Fault Relays, each can either energize or de-energize when that condition is detected:

• If its RA parameter has a positive value, the assigned condition energizes it.

• If that parameter is negative, that condition de-energizes it.

For example, if MODE:D RA 3 is assigned the value +Tran and is normally open, CR3 will be energized and its associated circuit will be closed whenever any analog input is outside the range of its transmitter testing limits. If it is given the value –Tran, that condition would cause CR3 to de-energize.

Whether energizing a relay opens or closes its circuit depends on the position of its NO/NC jumper, as described in the Discrete Out-put Jumpers section in Chapter 5 of IM300/H.

The states of these outputs can be displayed on the front-panel AUX readout by pressing the SCROLL key twice while the operating STATUS is displayed. “DGO= 12345” is then displayed, where each digit appears only if that discrete output is energized.

Fault Relays Discrete output CR1 is hard-wired as a fault relay, but can also be given one additional function. CR2 can be set to de-energize when-ever CR1 does by setting a jumper on that assembly (its assigned function then affects only its Modbus DO State discrete bit).

The operation of the controller’s fault relays and LED are described in the Fault Indicators section in Chapter 8 of IM300/H.

External Alarms You can use the controller’s discrete outputs to control external indi-cators (lights, horns, etc.) for any of the conditions described below. However, setting up and interpreting such alarms can be confusing because three different factors affect whether they indicate that the assigned condition does or does not exist:

• If the assigned function is positive, any non-fault relay energizes when that condition occurs. Relays with negative functions will de-energize when those conditions occur.

• The relay circuits in the controller can be set for normally-open operation (energizing the relay completes the circuit) or nor-mally-closed operation (energizing the relay opens the circuit).

• The alarm device itself may light or sound when its control cir-cuit is completed, or when it is opened.

September 2005 IM301 (6.1.3)


Table 3-4 Discrete output functions

Unless otherwise noted, the following descriptions assume each alarm circuit is set up to indicate that its assigned condition exists:

Always Set Relays assigned the +On function de-energize only if the controller loses power, those with the -On function are always de-energized. Fault Relays given the -On function never energize.

Automatic The Auto function indicates the controller is operating automatically.

Manual Override The MOR function indicates the antisurge control response is being manually controlled with no automatic surge protection (see Manual Override on page 33).

Never Set Relays assigned the +Off function are always de-energized, those with the -Off function de-energize only if the controller loses power. Fault Relays are often given the -Off function.

Output Failure The OutF function indicates a failure of analog output OUT1 (see Output Loopback Test on page 42).

Position Failure The PosF function indicates an excessive deviation of the measured valve position from its intended value (see Valve Position Test on page 43).

Pressure Limit The Lim function indicates a pressure limiting control response is greater than zero (see Pressure Limiting on page 82).

Code Function

Auto Automatic operation

Lim Pressure Limiting

MOR Manual Override (no automatic protection)

Off Never Set

On Always Set

Open control Valve Open

OutF analog Output Failure

PosF valve Position Failure

RT Recycle Trip condition

Run Run State

SerC Serial Communication Error

SO Safety On condition

Surg Surge Event

Tran Transmitter Failure

September 2005 IM301 (6.1.3)


Recycle Trip Relays assigned the RT function are asserted when the operating point moves to the left of the Recycle Trip Line (RTL). If the control-ler is operating manually, such indicators are not cleared until the Recycle Trip Response restores an adequate safety margin. If it is being manually operated, they are cleared as soon as the operating point moves back to the right of the RTL (see Recycle Trip Line on page 73 and Recycle Trip Response on page 80).

Run State The Run function indicates the controller is modulating the recycle valve to prevent surge (see Operating State on page 103).

Safety On Relays assigned the SO function are asserted when the controller detects a presumed surge and invokes the Safety On Response. Such indicators are not cleared until the surge count is zeroed (see Safety On Response on page 75).

Serial CommunicationError

The SerC function indicates the controller has failed to detect an expected transmission on its Port 1 or 2 communication network (see Serial Communication Errors on page 49).

Surge Event If the Surge Event Duration is not zero, relays assigned the Surg function are set when the event surge count reaches the Surge Event Threshold and remain set only until the event timer expires (see Surge Counters on page 76). Thus, such relays should be used to trip an edge-triggered response (such as an emergency shut-down) or device (such as a latched alarm).

If the Surge Event Duration is set to zero, relays given this function are set when the cumulative surge count reaches the Surge Event Threshold and remain set until that count is zeroed.

Transmitter Failure The Tran function indicates at least one analog input signal is not within its valid range (see Transmitter Testing on page 39).

Valve Open The Open function is asserted when the actuator control signal is greater than the low output clamp, thus indicating the control valve is open (see Output Clamps on page 100). It is particularly useful when that clamp is not zero, in which case it can be difficult to tell if the valve is open just by looking at the OUT readout.

September 2005 IM301 (6.1.3)


Figure 3-2 Communication with other controllers

Serial Ports Series 3 Plus Controllers are equipped with four serial ports for com-municating not only with other Series 3 Plus Controllers, but also with host computers and supervisory control systems:

• Port 1 is used for circulating information among the Series 3 Plus controllers regulating a single rotating equipment train. Antisurge Controllers use it primarily for coordinating control with companion Antisurge and Performance Controllers. A max-imum of eight controllers may be connected to any one Port 1 network.

• Port 2 is used for communicating load-sharing and performance override control information.

• Port 3 is used for computer communication and control, using the Modicon Modbus RTU protocol.

• Port 4 is functionally equivalent to Port 3, but is intended prima-rily for communication with a personal computer running one of our software support packages (Toolbox, for example).

Although these features are automatically enabled when required by the chosen controller features, it is necessary to set the ID Numbers that identify the controller to other devices on these networks and the baud rates and parity for several of the serial ports.

COMPRESSORCONTROLSCORPORATION

∆Manual

Auto

RT

Tracking

Fault

TranFail

Fallback

ComErr

DEV

OUTALT

Antisurge Controller AUX

Limit

.000

4.3

Status RUN

SO

MENU SCROLL

AUTO

MAN

∇

RESETSAFETY

ON

DISPLAYSURGECOUNT

DISPLAYLIMIT

Coordination (Port 1)


∆

Manual

Auto

RT

Tracking

Fault

TranFail

Fallback

ComErr

DEV

OUTALT

Antisurge Controller

AUX

Limit

.000

4.3

Status RUN

SO

MENU SCROLL

AUTO

MAN

∇

RESETSAFETY

ON

DISPLAYSURGECOUNT

DISPLAYLIMIT

Load Sharing (Port 2)


∆

Manual

Auto

Local

Tracking

Fault

TranFail

Fallback

ComErr

PV

OUTSP

Performance Controller

AUX

Limit

90.0

75.2

Status RUN

∇

Remote

MENU SCROLL

DISPLAYLOOP 2

DISPLAYLOOP 3

AUTO

MAN

90.0

REMOTE

LOCAL


∆

Manual

Auto

Local

Tracking

Fault

TranFail

Fallback

ComErr

PV

OUTSP

Performance Controller

AUX

Limit

75.2

50.4

Status RUN

∇

Remote

MENU SCROLL

DISPLAYLOOP 2

DISPLAYLOOP 3

AUTO

MAN

75.2

REMOTE

LOCAL

Load Sharing (Port 2)

September 2005 IM301 (6.1.3)


ID Numbers

Each Series 3 Plus Controller must be given both a

Controller ID Number

[MODE:D COMM 0] and a

Computer ID Number

[MODE:D COMM 0 •] by setting those parameters from the Engineering Panel:

• The


identifies it on Port 1. It must be unique among all controllers (except backups) in that network.

• The

Computer ID Number identifies it on Ports 2, 3, and 4. It

must be unique among all devices connected to any of those networks.

SerialCommunication

Formats

In order for two devices to successfully communicate, both must be set up to send and receive information at the same speed and in the same basic format (for example, number of bits per character):

• There are no configuration parameters for Port 1.

• The

Port 2 Baud Rate

[MODE:D COMM 2] can be set to 2400, 4800, or 9600. It is normally set to 9600. If you wish to mix Series 3 and Series 3 Plus Controllers, however, you must set the Port 2 baud rate to 2400 bps (the rate used by those older controllers).

• The

Port 3 Baud Rate

[MODE:D COMM 3] can be 4800, 9600, or 19.2k baud. The

Port 3 Parity

can be odd, even, or none.

• The same options are available for the

Port 4 Baud Rate

and the

Port 4 Parity

[MODE:D COMM 4].

Ports 3 and 4 both use one start bit, eight data bits, and one stop bit.

SerialCommunication

Errors

A Series 3 Plus Controller can experience two different kinds of serial communication errors:

• Hardware-level errors occur when the controller is unable to decode incoming characters of information.

• Control-level errors occur when the controller fails to detect expected serial communication activity on Port 1 or Port 2.

The controller indicates a hardware-level error by beeping and displaying an identifying message on the Engineering Panel, as described in Chapter 3 of IM300/H. Because the protocols used by the controller reject faulty messages (and usually provide for their retransmission), isolated hardware-level errors rarely affect the operation of the controller.

Control-level errors are indicated by lighting the front-panel ComErr LED, tripping any SerC relays, and setting the Modbus Port 1 or Port 2 Fail discrete bit. Because the interpretation of communication errors is highly site and application specific, your operator instruc-tions should list the various controllers from which this controller should be receiving transmissions and tell how to control and pro-tect the compressor while identifying and correcting these errors.

September 2005 IM301 (6.1.3)


The offending port can be determined and additional diagnostic information obtained via the following Engineering Panel tests:

• The

Serial Port 1 Test

[MODE COMM – 3] indicates (by control-ler ID number) the controllers from which Port 1 transmissions are or are not being received (regardless of whether or not such transmissions are needed or expected). The status of control-lers that are transmitting will display as “Good”, while the status of controllers from which no transmissions are being received will display as “Bad”. A serial error is indicated only if the status of a controller from which information is required is bad.

The interpretation of a Port 1 serial error depends on which of the features that utilize that port are employed (see Loop Decoupling on page 83, Auxiliary Limiting on page 83, Multisec-tion Compressors on page 85, Networked Compressors on page 92, Operating State Request Signals on page 103, and Redundant Control on page 36).

• The

Serial Port 2 Test

[MODE COMM – 2] will reveal whether or not any serial communication activity is being detected on that port. If so, the result will display as “PT2 GOOD”. If not, it will display as “PT2 BAD”.

Loss of Port 2 communications will prevent an Antisurge Con-troller from helping control a compressor network’s throughput (see Primary Capacity Control on page 92) or a load-sharing or single-compressor application’s performance override variable (see Performance Override on page 83).

ModbusConfiguration

The Modbus interface can be used to monitor the operation of the compressor and controller. The addresses and ranges of the available data are listed on the

Series 3 Plus Antisurge Controller Modbus Data Sheet

[DS301/M].

As described in the Computer Inhibit section in Chapter 1 of IM300/M, you can limit Modbus access by setting the

Read and Write Inhibit

[MODE:D LOCK 1] and

Write Inhibit Only

[MODE:D LOCK 2] parameters. In addition, the Numeric Values section in Chapter 2 of IM300/M of that manual tells how the input and holding registers are scaled and how their Port 3 values are affected by the

Modbus Register Scaling

[MODE:D LOCK 7].

September 2005 IM301 (6.1.3)



Chapter 4 Calculated Variables

This chapter tells how the Antisurge Controller calculates the values of various process conditions, and explains how to set up its Calcu-lated Variable Displays. Chapter 7 describes the additional variables calculated for multisection and networked compressors.

Pressures

In most applications, the controller must measure the suction and discharge pressures (P

s

and P

d

) and calculate either the compres-sion ratio (R

c

) or pressure rise across the compressor (

∆

P

c

):

Such calculations are valid only if both pressure inputs are scaled to the same maximum, absolute pressure. Thus, these four variables are calculated from the PV2 and PV3 Process Variables (see page 40), which should be scaled as dictated by the transmitter ranges and required calculations.

When P

d

is PV2 and P

s

is PV3,

∆

P

c

Substitution

[MODE:A SS 6 1] should be Off. However, you can configure the controller to use a differential

∆

P

c

measurement in place of either pressure input:

• If you connect the

∆

P

c signal to CH3 and set ∆Pc Substitution to Low, the suction pressure is calculated as:

• If you connect the ∆Pc signal to CH2 and set ∆Pc Substitution to High, the discharge pressure is calculated as:

Control algorithms applied to these pressures are unaffected by such substitutions. For example, limiting control always applies to Pd and Ps, whether calculated or directly measured.

Temperatures In some applications, the Antisurge Controller must also measure or compute various temperatures or temperature ratios. To ensure that calculations using such measurements are valid, they also employ specific Process Variables (see page 40), which should be scaled as dictated by the transmitter ranges and required calculations:

• the discharge temperature (Td) is PV5

• the suction temperature (Ts) is PV6

• the aftercooler temperature (Tac) is PV7

Because differential temperature transmitters are never used, ∆Tc Substitution [MODE:A SS 6 2] should always be Off.

Discharge Pressure

Suction Pressure

Compression Ratio

Pressure Rise

Rc Pd Ps⁄= Pc∆ Pd Ps–=

Ps Pd Pc∆– PV2 PV3–= =

Pd Ps Pc∆+ PV3 PV2+= =

Discharge Temperature

Suction Temperature

Temperature Ratio

September 2005 IM301 (6.1.3)

52 Chapter 4: Calculated Variables

Head Application functions that calculate reduced polytropic head use the following defining equation:

where:

hr = reduced head

Rc = Compression Ratio (Pd / Ps )

σ = polytropic head exponent (sigma)

The polytropic head exponent is calculated from the temperature and compression ratios:

The resulting exponent is then passed through a first-order lag filter governed by the Sigma Filter Constant [PID:A Tf 2].

If the polytropic head exponent is nearly constant, this calculation can be configured to use the Default Sigma [COND:A CONST 4] by enabling the Constant Sigma [MODE:A fC 2] option. However, this usually has the same effect as selecting an fA mode that calculates proximity to surge as a function of Rc rather than a function of hr.

Speed The Rotational Speed Source [MODE:A ANIN 4] specifies whether the controller should measure rotational speed (N) using its CH4 analog input [AN IN 4 Off] or obtain it via serial communication from a companion Series 3 Plus Controller [AN IN 4 equals that compan-ion’s Controller ID Number]:

• If that source is also specified as the companion Load-Sharing Controller [MODE:A SS 4] by setting that parameter equal to its Controller ID, it must be a Performance Controller that uses an analog input to monitor speed. In non-load-sharing applications, the Recycling Gain [COND:A M 0] must also be set to zero.

• If that source is not specified as the companion Load-Sharing Controller [SS 4 ≠ its ID], it must be a Speed or Fuel Controller that is regulating the compressor’s rotational speed.

Equivalent speed (Ne) is a dimensionless function of rotational speed, suction temperature, and gas composition. Although it is often the third coordinate of an invariant compressor performance map, our methods of computing proximity to surge do not require its explicit calculation.

Reduced Head

Polytropic HeadExponent

hr Rcσ 1–( ) σ⁄=

σ Td Ts⁄( )log Pd Ps⁄( )log⁄=

Rotational Speed

Equivalent Speed

Note:Because it is difficult to determine the cause of a surge if the rota-tional speed is unknown, the speed of every compressor should be measured by at least one controller.

September 2005 IM301 (6.1.3)


Power The “power algorithm” (fA 51) calculates proximity to surge from the compression ratio and reduced power (jr). The X Coordinate Char-acterizer [COND:A f(X) 3 # and X 3 #] defines the dependence of reduced power on the rotational speed, which means that function should normally equal its argument:

The drive power signal (J) is usually connected to CH1 (J = PV1), so the Safety On Surge Detection (see page 75) can use rapid power fluctuations as an indication of surging. However, that signal can be connected to any otherwise unused input if it is defined as the f5 Argument [MODE:A SS 9] and the General Characterizer [COND:A f(X) 5 # and X 5 #] is defined as a simple inverse function:

In this case, PV1 should be defined as a constant by setting the CH1 Process Variable Gain to zero and its Process Variable Bias to the desired constant value. Because the controller detects surge by monitoring SV1 (that is, the CH1 signal variable, which is unaffected by the PV1 scaling), it can be configured to detect surge by monitor-ing whatever signal you do connect to CH1, which will in turn have no effect on the proximity-to-surge calculation.

You can compensate for mechanical power losses by defining the net power as a function of speed or power:

• To define net power as a function of speed, incorporate that cor-rection into the f3 characterizer:

• To define net power as a function of gross power, incorporate that correction into the f5 characterizer:

if , then

if , then

Net power can also be defined as the ratio of any single-input vari-able and a function of another:

For a steam turbine driven compressor, for example, PV1 could be a steam flow rate and f5 a function of steam temperature. However, such rarely used approximations are not generally recommended.

Drive Power

Reduced Power

j rJ

N Ps⋅--------------- PV1

f3 N( ) f5 Z( ) Ps⋅ ⋅----------------------------------------= = f3 N( ) N=

J 1 f5 J( )⁄= f5 J( ) J 1–=

Jnet N⁄ Jgross f3 N( )⁄= f3 N( ) N Jgross Jnet⁄⋅=

Jnet PV1 f5 Jgross( )⁄=

PV1 Jgross= f5 Jgross( ) Jgross Jnet⁄=

PV1 1= f5 Jgross( ) 1 Jnet⁄=

Jnet PV1 f5 Z( )⁄=

September 2005 IM301 (6.1.3)


Flow Rates A variety of flow rates and measurements are calculated for control and informational purposes. Proximity to Surge (see page 63) is usually calculated from a reduced flow variable based on a scaled, selected, or otherwise calculated measurement of the total flow through the compressor. Several other features calculate various Mass Flow Rates (see page 58).

The more complex flow calculations that might be required in multi-section compressor applications are discussed in Chapter 7.

Reduced Flow Proximity to surge calculations usually employ a dimensionless, reduced flow variable (qr) that is defined as:

where:

∆Po = differential pressure drop across an orifice plate or other flow measuring restriction

Ps = suction pressure

∆Po must be a measurement of the total suction or discharge flow, and we refer to the corresponding dimensionless flows as reduced flow in suction (qr,s) or in discharge (qr,d):

Calculated FlowMeasurement

Because the total flow measurement can optionally be selected from more than one source, compensated for a suction control valve, or calculated by combining a sidestream flow with that through another compressor section, we refer to it generically as the calculated flow measurement (∆Po,c). In the simplest case, however, this will be a directly-measured, suction or discharge differential pressure signal connected to analog input CH1 (in which case ∆Po,c = PV1).

q r Po∆ Ps⁄=

q r s, Po s,∆ Ps⁄= q r d, Po d,∆ Ps⁄=

September 2005 IM301 (6.1.3)


Figure 4-1 Using dual flow transmitters

Dual FlowTransmitters

A differential pressure signal is generally unsuitable for control purposes below about ten percent of its transmitter span. Thus, in applications that require frequent or sustained operation at low ori-fice pressure drops, the Antisurge Controller can switch to a second flow input that is presumably connected to a transmitter with a lower range than that connected to CH1.

This feature is particularly useful when the orifice pressure drops during normal operation are much higher than those encountered while the compressor is starting, stopping, or idling. For example, hydrogen compressors are often charged with nitrogen at such times, which yields much lower orifice pressure differentials.

As shown in Figure 4-1, the higher- and lower-spanned transmitters should be connected to CH1 and the specified Low Flow Input [MODE:A SS –], respectively, and their process variables should be scaled as percentages of the same maximum pressure drop. The proximity-to-surge calculation would then use the low flow process variable as its flow measurement until its signal variable reached 90 percent. It would then use PV1 until the low flow signal variable fell back below 75 percent.

For example, assume a 0 to 12.5 kPa transmitter is connect to CH1 and a 0 to 2.5 kPa signal is connected to CH7. SS – should then be set to PV7. If the gain and bias for PV1 are set to 1.000 and 00.0, the gain and bias for PV7 should be 0.200 and 00.0 (so both signals would rise to 20 percent as ∆Po rises to 2.5 kPa). The proximity-to-surge calculation would then use PV7 until ∆Po reached 2.25 kPa, after which PV1 would be used until SV7 fell back below 1.875 kPa.

If the specified Low Flow Input failed, PV1 would be used as the flow measurement regardless of its range. If CH1 failed, the Low Flow Input would be used as long as its signal variable was no higher than 90 percent. Above that threshold, the controller would invoke its Default Output Fallback (see page 67).

This feature can be disabled by setting the Low Flow Input to either Off or 1, in which case PV1 is used as the only analog flow input.

UIC

∆Po,high

1 n Connect ∆Po,low to any appropriateinput CHn, then set SS – = n

FT1 FT2

∆Po,low

September 2005 IM301 (6.1.3)


Figure 4-2 Compensating ∆Po for a suction control valve

Control ValveCompensation

If flow is measured in suction and there is a control valve between the flow element and compressor inlet, the controller can be config-ured to compensate its calculated flow measurement for the change in pressure across that restriction (see Figure 4-2):

First, connect the suction pressure signal (measured at the com-pressor inlet) to analog input CH3. Then connect a second pressure signal (Pfe, measured at the flow measuring element, upstream from the valve) to any otherwise unused analog input. Finally, set the Flow Element Pressure Input [MODE:A SS 8] equal to that pressure input’s channel number.

If either pressure measurement fails, this compensation is discon-tinued. This does not compromise surge protection, because the actual flow measurement (∆Po) will always be lower than the equiva-lent suction flow measurement (∆Po,s).

FT

UIC

PT

Ps∆Po

1 3n

PT

Pfe

Connect Pfe to any unused inputCHn, then set SS 8 = n

Po c,∆ Po s,∆ Po∆ Pfe Ps⁄⋅= = Po∆ PV1=

Note:Appendix F discusses the application (if any) of this feature to each fA Mode. Unless used as described for your selected fA Mode, this compensation must be explicitly disabled by setting SS 8 to Off.

September 2005 IM301 (6.1.3)


Discharge FlowMeasurement

When the flow is measured in discharge, an invariant proximity to surge can be calculated from the reduced flow in discharge (qr,d). However, practical considerations often dictate the calculation and use of an equivalent reduced flow in suction (qr,s):

This calculation is implemented in fA modes 63 and 67.

Because Td /Ts = (Pd/Ps)σ for polytropic compression, the Default

Sigma [COND:A CONST 4] can be used to calculate the equivalent suction flow measurement from pressure measurements only. Thus, if the Constant Sigma [MODE:A fC 2] option is enabled, fA 67 will calculate ∆Po,s as.

This option is not available in fA 63, where the required correction can be incorporated into the Y Coordinate Characterizer [f1(Rc)].

Aftercooler FlowMeasurement

When the flow is measured downstream from an aftercooler, an equivalent suction flow measurement can be calculated as:

This calculation is explicitly implemented in fA 68. It can also be employed in fA 63 if aftercooler measurements (∆Po,ac and Tac) are connected to CH1 and CH5 in place of the discharge measurements (∆Po,d and Td).

If both Ts and Tac are controlled, their ratio will be nearly constant. Thus, if the Constant Sigma [MODE:A fC 2] option is enabled, fA 68 will calculate ∆Po,s without any temperature measurements:

Po s,∆ Po d,∆ Pd Ps⁄( ) Ts Td⁄( )⋅ ⋅=

q r s,2 Po s,∆

Ps-------------- Po d,∆

Pd

Ps2

------Ts

Td

------⋅ ⋅= =

Po s,∆ Po d,∆ Pd Ps⁄( ) Td Ts⁄( )⁄⋅=

Po d,∆ Rc Rcσ⁄⋅ Po d,∆ Rc

1 σ–⋅==

Po c,∆ Po ac,∆ Pd Ps⁄( ) Ts Tac⁄( )⋅ ⋅=

q r s,Po s,∆Ps

-------------- Po ac,∆Pd

Ps2------

Ts

Tac

--------⋅ ⋅= =

Po s,∆ Po ac,∆ Pd Ps⁄⋅∝ Po ac,∆ Rc⋅=

September 2005 IM301 (6.1.3)


Mass Flow Rates The Antisurge Controller uses the same basic formula and compen-sating inputs to calculate several mass flow rate variables:

• The Reported Flow (see page 86) of any Application Function between 61 and 69 is a squared mass flow rate.

• The Displayed Flow (see page 61) can be viewed via the AUXil-iary readout.

Assuming little variation in gas composition and compressibility, the mass flow rate (W) through an orifice plate can be calculated as:

where:

W = mass flow rate

∆Po = pressure drop across the orifice

P = absolute pressure

T = absolute temperature

The Antisurge Controller calculates its mass flow rates as:

or

where:

C = an appropriate scaling coefficient

∆Po = an appropriate flow measurement (usually a desig-nated analog input signal or process variable)

Pc = Compensating Pressure

Tc = Compensating Temperature

The scaling coefficient should be proportional to the inverse of the maximum flow rate, calculated as:

where:

Tmf = absolute temperature at maximum flow rate

MaxTT = absolute temperature corresponding to the transmit-ter’s maximum signal

∆Po,mf = orifice pressure drop at maximum flow

MaxFT = orifice pressure drop corresponding to the transmit-ter’s maximum signal

Pmf = absolute pressure at maximum flow

MaxPT = absolute pressure corresponding to the transmitter’s maximum signal

W Po∆ P⋅ T⁄∝

W C Po∆ Pc⋅ T⁄ c⋅= W2 C Po∆ Pc⋅ T⁄ c⋅=

CTmf

MaxTT------------------

MaxFT

Po mf,∆------------------

MaxPT

Pmf------------------⋅ ⋅=

September 2005 IM301 (6.1.3)


Tmf and MaxTT must be expressed in the same absolute units (for example, °R), as must ∆Po,mf and MaxFT (for example, psi) and Pmf and MaxPT (for example, psia).

CompensatingPressure

All mass flow calculations use the same compensating pressure and temperature, which are calculated as:

Pc = absolute orifice pressure = Po + Pr

Po = measured variable (see page 40) for the analog input designated as the Compensating Pressure Input [MODE:D fD 2]

Pr = absolute pressure when Po is zero, defined by the Compensating Pressure Offset [COND:D CONST 2]

Tc = absolute orifice temperature = To + Tr

To = measured variable for the analog input designated as the Compensating Temperature Input [MODE:D fD 3]

Tr = absolute temperature when To is zero, defined by the Compensating Temperature Offset [COND:D CONST 3]

If Po and To are scaled to absolute units, Pr and Tr should be zero.

CompensatingTemperature

Note: The measured-variable scaling should be chosen to yield pressures that are less than sixteen times the temperature.

September 2005 IM301 (6.1.3)


CalculatedVariableDisplays

The AUXiliary readout can display any of the calculated variables listed in Table 4-1. Each such readout is enabled or disabled by the indicated parameter.

The Reduced Head, Polytropic Head Exponent, Compression Ratio, and Temperature Ratio readouts will be meaningless and should be disabled unless your chosen fA Mode calculates those variables. Special scaling is applied only to the Displayed Speed, Displayed Flow, and Displayed Net Flow. Those readouts should be enabled only if you supply the required inputs.

In the event that one or more of the inputs used to calculate these variables fail, the Fallback Strategies can be configured to substitute default values for either those inputs or the calculated variable. The resulting fallback value would then be displayed.

The Flow Variables Decimal [COND:D DISPLAY 1 5 •] sets the loca-tion of the decimal point (if any) in the Flow and UsrQ readouts. It specifies the digit the decimal will replace, where the fifth digit is left-most (most significant) and the first is right-most (least significant). Thus, if the calculated Flow is 98765, the five possible values of that parameter would display it as follows:

When setting this parameter from the Engineering Panel, you can try as many different values as you want, then press ENTER when you see the desired display format.

To obtain the most precise readouts, scale the calculations to yield five-digit maximum flows. For example, if you want the Flow readout to range from 0 to 600.0, set the Displayed Flow Coefficient such that the maximum result (W) is 60000. Then set the Flow Variables Decimal to 2 so the four most significant digits are displayed with a decimal after the third. This will give more precise readouts than you would get by scaling the calculation to yield a maximum value of 00600 with no decimal.

Table 4-1 Available calculated variable readouts

0: 98765 1: 9876 2: 987.6 3: 98.76 4: 9.876

Readouts Enabling Parameter

Hpr = #.### , Sigma= .### Polytropic Exponent Display [COND:D DISPLAY 1 1]

Rc= ##.## Compression Ratio Display [COND:D DISPLAY 1 2]

Rt= #.## Temperature Ratio Display [COND:D DISPLAY 1 3]

Speed= ##### Rotational Speed Display [COND:D DISPLAY 1 4]

Flow = ##### Mass Flow Display [COND:D DISPLAY 1 5]

UsrQ = ##### Net Flow Display [COND:D DISPLAY 1 7]

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If Auxiliary Display Reset [MODE:D LOCK 9] is disabled, Calculated Variables will be displayed until another variable is selected. Other-wise, the operating state display is restored 60 seconds after the MENU or SCROLL key was last pressed.

Displayed Speed If the Rotational Speed Display [COND:D DISPLAY 1 4] is enabled, the value of the Speed readout is calculated as:

where:

D14 = Rotational Speed Coefficient [COND:D DISPLAY 1 4 HIGH]

N = normalized Rotational Speed (see page 52)

Displayed Flow If the Mass Flow Display [COND:D DISPLAY 1 5] is enabled, the value of the Flow readout is calculated as:

where:

D15 = Displayed Flow Coefficient [COND:D DISPLAY 1 5 HIGH]

Pc = Compensating Pressure (see page 59)

Tc = Compensating Temperature (see page 59)

∆Po = Mass Flow Input [MODE:D fD 1] signal variable (if dis-abled, the Calculated Flow Measurement is used)

As explained on page 60, the position of the decimal point is set by the Flow Variables Decimal [COND:D DISPLAY 1 5 •].

You can configure an external numeric or graphical display for this flow by assigning the Flow function to analog output OUT2 (see Analog Outputs on page 42). The value of that output signal (in per-cent of span) is then calculated as:

where:

β0 = OUT2 Mass Flow Coefficient [COND:D β 0]

For example, if Flow varies from 0 to 10,000, setting β 0 to 10.0 will configure OUT2 to vary from 0 to 100 percent.

Speed D14 N⋅=

Flow D15 Po∆ Pc Tc⁄⋅⋅=

OUT2 β0 Flow⋅ 1 000,⁄=

September 2005 IM301 (6.1.3)


Displayed NetFlow

If the Net Flow Display [COND:D DISPLAY 1 7] is enabled, the value of the UsrQ readout is calculated by subtracting a calculated recycle flow from the Displayed Flow:

where:

Act = displayed output

=Actuator Control Signal (see page 99) or its complement

D17 = Net Flow Coefficient [COND:D DISPLAY 1 7 HIGH]

f2A() = Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #]

f2D() = Recycle Flow Characterizer [COND:D f(X) 2 # and X 2 #]

Flow = Displayed Flow (see page 61)

Pd = Discharge Pressure (see page 51)

Rc = Compression Ratio (see page 51)

Td = Discharge Temperature (see page 51)

Valve manufacturers usually provide the information needed to define the characterizers and coefficients in this equation.

As explained on page 60, the position of the decimal point is set by the Flow Variables Decimal [COND:D DISPLAY 1 5 •].

You can configure an external numeric or graphical display for this flow by assigning the UsrQ function to analog output OUT2 (see Analog Outputs on page 42). The value of that output signal (in per-cent of span) is then calculated as:

where:

β0 = OUT2 Mass Flow Coefficient [COND:D β 0]

UsrQ Flow D17 f2D Act( ) f2A Rc( )Pd

Td

----------⋅ ⋅ ⋅–=

OUT2 β0 UsrQ⋅ 1 000,⁄=

September 2005 IM301 (6.1.3)



Chapter 5 Proximity to SurgeThis chapter tells how to set up the proximity-to-surge calculation and fallbacks.

ApplicationFunction

The specific method that a Series 3 Plus Antisurge Controller uses to calculate a compressor’s proximity to surge is defined by setting the Application Function [MODE:A fA], which selects one of several “fA Mode” equations sharing the general form:

where:

f1(Y) = Y Coordinate Characterizer

f3(N) = X Coordinate Characterizer

f5(U5) = General Characterizer

K = Surge Limit Line Coefficient

N = rotational speed

Pd = discharge pressure

Ps = suction pressure

Td = discharge temperature

Ts = suction temperature

U5 = secondary coordinate specified as the f5 Argument

X, Y = primary coordinates of the compressor map

This function is scaled so that Ss equals one when the compressor is operating on its surge limit line, and will be less than one when the operating point is safely to the right of the SLL. In theory, this could be accomplished without a Surge Limit Line Coefficient [SPEC:A K], simply by appropriately scaling the various Characterizing Func-tions. In practice, K is usually given a nominal value of 0.5 and the characterizers are set accordingly. Minor retuning can then be accomplished by simply varying K.

In most fA Modes, the X coordinate is the Reduced Flow (see page 54), although Reduced Power (see page 53) can be used when no flow measurement is available. The Y coordinate is generally the Compression Ratio or Reduced Head (see page 52), depending on the variability of the Polytropic Head Exponent (in this discussion, hr is used as the generic case). U5 is most often the guide vane angle (α). Appendix F describes the generally recommended fA Modes, while Table F-1 summarizes their analog input signals.

Ss

K f1 Y( ) f5 U5( )⋅ ⋅X

------------------------------------------K f1 Ps Pd Ts Td, , ,( ) f5 U5( )⋅ ⋅

Po∆ Ps f3 N( )⋅[ ]⁄-------------------------------------------------------------------------= =

September 2005 IM301 (6.1.3)

64 Chapter 5: Proximity to Surge

Figure 5-1 Defining the minimum safe flow as a function of head

Filtering A first-order-lag software filter governed by the DEV Filter Constant [PID:A Tf 1] is applied to the fA mode’s numerator and denominator.

CharacterizingFunctions

As shown in Figure 5-1, the Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the shape of the surge limit line. This is usually the minimum reduced flow (qr) at each of ten values for the reduced head (hr), so that proximity to surge is the ratio of that mini-mum flow (at the current head) to its actual value:

The General Characterizer [COND:A f(X) 5 # and X 5 #] can then be used to further define either coordinate variable or the surge limit as a function of the f5 Argument [MODE:A SS 9]:

• If SS 9 is Off, this argument is the Polytropic Head Exponent (σ), which is sometimes a good measure of gas composition.

• Otherwise, this argument is the corresponding process variable (for example, if SS 9 equals 7, f5 is a function of PV7). This is most often used to define the surge limit as a function of the guide vane angle.

In fA 51 applications, the X Coordinate Characterizer [COND:A f(X) 3 # and X 3 #] is used to calculate Reduced Power (see page 53). Otherwise, f3 should be defined as a constant.

In applications using fA 34 or 35, the Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #] is used to calculate an equivalent flow measurement (see Equivalent Flow Measurements on page 85). In series Load Balancing (see page 93) applications, the Balancing Variable Characterizer [COND:A f(X) 6 # and X 6 #] usually defines the load as a function of speed or compression ratio. Finally, the Control Line Characterizer [COND:A f(X) 4 # and X 4 #] is used to define various Control Lines (see page 71).

0

hr,3

qr=10

hr=10

qr,3

SurgeLimitLine

COND:A X 1 n = hr,nCOND:A f(X) 1 n = qr,n

qr min,2 f hr( )= Ss qr min,

2 qr2⁄ f hr( ) qr

2⁄= =

September 2005 IM301 (6.1.3)


Figure 5-2 Proximity to surge for a fixed-geometry compressor

Each of these functions is defined by ten data pairs representing the argument and corresponding function values. The controller then uses linear interpolation to calculate intermediate values.

You must select eight values for each function’s independent vari-able (X1 through X8), each of which must exceed (and cannot equal) its predecessor. These are defined by the corresponding COND X # # parameters. X0 and X9 are predefined as 0.00 and 10.00 for f1 and f2 and as 0.000 and 1.000 for f3 through f6.

You must also determine the ten corresponding values of each func-tion’s dependent variable [Yn = f(Xn)], which are defined by setting the corresponding COND f(X) # # parameters.

Beginning with software revision 756-002, the values returned by the f1, f2, f3, and f5 characterizers can be viewed via the front-panel AUX readout. Whenever a particular characterizer is not being cal-culated, however, its result will display as “–.– –”.

Fixed-GeometryCompressors

Although three dimensionless-coordinates [reduced head (hr), reduced flow (qr), and equivalent speed (Ne)] are required to fully map the operation of a fixed-geometry compressor, only two of them are needed to calculate an invariant proximity to surge. In general, (hr , qr) is the only practical coordinate system. Reduced power (jr), which is essentially the product of head and flow, can be substituted for qr when no flow measurement is available, and reduced head can often be adequately characterized as a function of Rc alone.

hr

O qrf1(hr)

PS

Ne,3

Ne,2

Ne,1

qr,SL

hr

O qrf1(hr)

S

Ne

qr,SL

P

Ss =f(hr)qr

Proximity to surge is calculated by dividing the minimum flow at the cur-rent head [f1(hr)] by the actual flow.

At the surge limit, qr and f1(hr) converge to the minimum qr at the

current, unknown value of Ne.

Note:If invalid characterizer points are downloaded using the Configurator program, the controller will substitute a default set of X values and set all f(X) values to 1.00. The parameter checksum displayed on its engineering keypad will then be different from that indicated by Con-figurator program.

September 2005 IM301 (6.1.3)


Figure 5-3 Proximity to surge for a variable-geometry compressor

If we draw performance curves that plot hr against qr at various equivalent speeds (Ne), as shown in the left panel of Figure 5-2, we can calculate Ss by comparing the actual reduced flow to the value it would have if the compressor was at its surge limit with the same reduced head, as defined by K · f1(hr).

The equivalent speed need not be known, even though it would be different for those two points and might be changing:

• If the operating point approaches the surge limit along a line of constant Ne (as shown), qr and f1(hr) will converge.

• If the operating point approaches the surge limit along a line of constant hr, qr will decrease to f1(hr) and the two values of Ne will converge.

• If all three variables change, the difference between qr and f1(hr) will still decrease (and Ss will still rise) if the new operating point is closer to the surge limit line.

Because this approach is practically invariant to all process condi-tions, there is no need to further characterize the surge limit as a function of gas composition or inlet temperature.

Variable-GeometryCompressors

Four dimensionless-coordinates (generally reduced head, reduced flow, equivalent speed, and guide vane angle) are needed to quan-tify the operation of a variable-geometry compressor, but only three of them (head, flow, and vane angle) are needed to calculate an invariant proximity to surge (see Figure 5-3). Ideally, the surge limit would be characterized as:

In the Series 3 Plus Antisurge Controller, however, this ideal is approximated using separate functions of head and vane angle:

O qr

hr

Ss =f(hr) · f(α)

qr

α1

Ne,2

Ne,3

Ne,1

α2 α3

Ss K f α hr,( ) qr⁄⋅=

Ss K f5 α( ) f1 hr( ) qr⁄⋅ ⋅=

September 2005 IM301 (6.1.3)


FallbackStrategies

The Antisurge Controller offers a wide variety of fA Modes that allow you to tailor its proximity-to-surge computation to your specific appli-cation. In general, the more complicated modes will provide more energy savings, because they allow you to tune the controller more aggressively. But they are also more likely to succumb to transmitter failures, because they require more inputs.

In many such cases, continued surge protection can be provided by substituting an approximate constant value for the missing input or some intermediate calculation based on that input. At the very least, it is usually better to revert to minimum flow control than to continue controlling on the basis of a suspect input.

Toward this end, the Antisurge Controller offers a number of fallback strategies. Each of these can be enabled or disabled by setting its Fallback [MODE:A fD 3 #] parameter, and most utilize one or more fallback constant [COND:A CONST #] parameters.

Depending on the selected fA Mode, more than one of these algo-rithms might be applicable to a given input failure or combination of failures. In such cases, the controller will select the fallback mode or modes (from among those that have been enabled) that utilize as many valid inputs as possible.

The front-panel FallBack indicator will light whenever one or more of the fallback options is active.

In addition to the optional algorithms discussed below, the following fallbacks are always applied if the indicated conditions are detected:

• If the calculated flow measurement is being compensated for a flow restriction (see Control Valve Compensation on page 56), that compensation is discontinued if either required pressure measurement fails. Because the actual flow measurement in such applications will always be less than a measurement of the true flow would be, this does not compromise surge protection.

• Suction or discharge Pressure Limiting (see page 82) is sus-pended if a required analog input fails.

Default OutputFallback

The purpose of the Default Output Fallback [MODE:A fD 3 1] is to open the recycle valve far enough to prevent surge under the worst possible conditions when all of the less-drastic fallbacks are either disabled or inapplicable.

During normal operation, the controller continuously calculates a fil-tered control signal value that is relatively unaffected by transients caused by an input failure. When this fallback is triggered, the actu-ator control signal is ramped to the higher of this filtered value or the Fallback Minimum Recycle [COND:A CONST 1]. Any SO and RT relays are also cleared, as are those LEDs. This fallback then

September 2005 IM301 (6.1.3)


remains active until two seconds after the conditions that triggered it are corrected:

• Most fA Modes maintain a flow measurement (∆Po). If fD 31 is enabled in such an application, it is triggered when the flow input is outside its acceptable range, or the controller requires but fails to receive a valid flow measurement from a designated Adjacent Section Controller [MODE:A SS 5].

• Other fA Modes maintain a minimum mass flow (W). If fD 31 is enabled in such an application, it is triggered when the associ-ated flow, temperature, or pressure input is outside its acceptable range or if the controller requires but fails to receive a valid mass flow from the Adjacent Section Controller.

• A cold recycle controller (fA 00) initiates this fallback if it fails to receive a valid flow from any companion controller.

• This fallback is also initiated if the controller is tracking the out-put signal of another device and the analog input for that signal fails (see Output Tracking on page 102).

While this fallback is active, the Auto LED flashes and the output is held constant, although you can initiate manual operation and set the output signal to any desired value. However, you should not do so on the basis of the front-panel DEV display — its value will be based on that of the failed input! If you restore automatic operation while the fallback condition still exists, the control signal will remain constant at the manually set value.

Minimum FlowFallback

The purpose of the Minimum Flow Fallback [MODE:A fD 3 2] is to maintain a worst-case minimum flow when that variable can be computed but its dynamic minimum limit cannot. If this fallback is triggered, the controller will calculate Ss as the ratio of its Default Minimum Flow [COND:A CONST 2] and the calculated flow mea-surement (∆Po,c) or mass flow rate:

It will then raise the recycle flow rate as needed to keep the compli-ment of this ratio above the desired surge control margin:

This fallback is usually triggered only if several pressure or tempera-ture inputs fail. However, it might also be triggered by the failure of a single input signal if no less-drastic fallback mode is appropriate to

Note: For fA mode 51, which calculate Ss from a power measurement, this the only fallback currently supported.

Ss Const 2 Po c,∆⁄= or Ss Const 2 W2⁄=

1 Const 2 Po c,∆⁄( )– b f4 U4( )⋅ Po c,∆ Const 21 b f4 U4( )⋅–--------------------------------≥→≥

September 2005 IM301 (6.1.3)


your chosen fA Mode, or if all such modes have been disabled. If fD 32 is Off, conditions that would otherwise trigger this fallback will trigger the Default Output Fallback instead.

Normally, ∆Po,c is simply the process variable for the flow input (PV1). However, if that measurement is compensated for a suction flow control valve (see Control Valve Compensation on page 56), the compensated value is used unless a pressure input required to calculate it fails. In that event, the uncompensated (and therefore lower) value of PV1 would be used.

There is no specific fallback that allows fA 34 to calculate its ∆Po,c when the adjacent stage pressure input (CH5) fails. However, that condition would cause the Reported Flow Characterizer to assume the value of its final defining point [COND:A f(X) 2 9]. An adequate fallback can thus be fashioned by assigning appropriate values to that characterizer point and the Default Minimum Flow.

CompressionRatio Fallback

If the selected fA Mode calculates the compression ratio, enabling the Compression Ratio Fallback [MODE:A fD 3 3] configures the controller to substitute the Default Compression Ratio [COND:A CONST 3] when the discharge pressure input fails (a suction pres-sure input failure would trigger the Minimum Flow Fallback).

Application functions that calculate the Polytropic Head Exponent from the compression ratio will not use the default ratio to calculate sigma. Instead, the Sigma Fallback should be enabled to allow them to use a default exponent. Such modes will also use the Polytropic Head Fallback in preference to this strategy if both are enabled.

Sigma Fallback Some fA Modes calculate the Polytropic Head Exponent (sigma) from the temperature and compression ratios. Because a worst-case value of this variable can often be predicted from a knowledge of the process, you can enable the Sigma Fallback [MODE:A fD 3 4] to configure such modes to substitute the Default Sigma [COND:A CONST 4] when any input used only to calculate that exponent fails.

Speed Fallback If the chosen application function requires the Rotational Speed and the Speed Fallback [MODE:A fD 3 5] is enabled, the controller will substitute the Default Speed [COND:A CONST 5] when the analog speed input or communication with the designated companion tur-bine controller fails. If this fallback is disabled, failure of the speed signal will trigger the Minimum Flow Fallback.

Note:If the selected fA Mode calculates sigma, you must define a Default Sigma even if the Sigma Fallback is disabled (the default value is always used during startups and shutdowns, when the calculated value might be inaccurate).

September 2005 IM301 (6.1.3)


This fallback should be enabled if speed is the argument of an X Coordinate Characterizer that is defined as a constant. Ss would then be correctly calculated from any Default Speed (however, a fallback condition would still be indicated). If this fallback is disabled, speed failure would unnecessarily trigger the minimum flow fallback.

Function 5Fallback

When the selected fA mode includes the General Characterizer [COND:A f(X) 5 # and X 5 #] and the Function 5 Fallback [MODE:A fD 3 6] is enabled, the controller will use the Default f5 Argument [COND:A CONST 6] when the input defined as the f5 Argument [MODE:A SS 9] fails. If this fallback is disabled, failure of that input signal will trigger the Minimum Flow Fallback.

If the General Characterizer is defined as a constant, its argument will have no effect on the value of Ss. Its argument should then be an input for which the alarm limits can be set to 00.0 and 102.4, so that it is always valid. If that is not possible, you should enable this fallback. The controller will then calculate the correct value for Ss from the Default f5 Argument, regardless of its value (however, it would still signal a fallback condition).

Adjacent SectionFlow Fallback

If the selected fA Mode requires a flow measurement or mass flow from an adjacent section controller, a Port 1 failure would trigger the Default Output Fallback (if it is enabled).

However, you can configure the controller to use its Default Adja-cent Section Flow [COND:A CONST 7] in any other calculation that requires the missing flow by enabling the Adjacent Section Flow Fallback [MODE:A fD 3 7]. If the Default Output Fallback is disabled, this default reported flow will also be used in the Ss calculation.

Valve-SharingFallback

In valve-sharing applications, enabling the Valve Sharing Fallback [MODE:A fD 3 8] of the primary controller configures it to use an Alternate K [COND:A CONST 8] for the Surge Limit Line Coefficient [SPEC:A K] when it loses contact with any secondary controller.

If this fallback is disabled, loss of communication with any second-ary controller will trigger the Default Output Fallback (if it is enabled).

Polytropic HeadFallback

Enabling the Polytropic Head Fallback [MODE:A fD 3 9] configures “no-flow” fA modes to calculate that variable from the suction and discharge temperatures and the Default Sigma [COND:A CONST 4] if the discharge pressure input fails:

If enabled, this approach will be used in preference to the Compres-sion Ratio Fallback.

Rcα Td Ts⁄= hr

Td Ts⁄( ) 1–

σ------------------------------

Td Ts–

Ts σ⋅------------------= =

September 2005 IM301 (6.1.3)



Chapter 6 Antisurge ControlThis chapter tells how to set up the algorithms that calculate various control responses and select the required recycle flow rate.

Figure 6-1 Typical control lines for antisurge control responses

Control Lines Various control actions are triggered when the operating point crosses the corresponding control lines:

• The Antisurge PI Response increases the recycle rate when the operating point is to the left of the Surge Control Line, and reduces it when that point is to the right of that line.

• The Recycle Trip Response ratchets the control valve open when the operating point is to the left of the Recycle Trip Line.

• The Safety On Response moves the surge control line to the right if the operating point crosses the Safety On Line.

• The Tight Shut Off Response (see page 101) fully closes the control valve when the operating point is to the right of the Tight Shut-Off Line and the output is at its minimum clamp.

Just as the surge limit line (SLL) is the locus of points for which Ss equals one, each control line is the locus of points for which:

where

f4 = Control Line Characterizer [COND:A f(X) 4 # and X 4 #]

U4 = Control Line Argument [MODE:A fC 1]

We can then define the margin (or distance) between any control line and its reference line (usually the SLL) as:

qr

hr

SlopeRTL = 1 – b 1 – CR SO + RT

Slope

TSL

= Slope

SCL

– d 1 Slope

SCL

= 1 – b 1 – CR SO – CR D

Slope

SOL

= 1 + SOSlope

SLL

= 1

Safet

y On

Line

Surge Limit L

ine

Recycle Trip Line

Surge Control Line

Tight Shut-Off Line

Ss 1 bias f4 U4( )⋅+=

m inarg bias f4 U4( )⋅=

September 2005 IM301 (6.1.3)

72 Chapter 6: Antisurge Control

In addition, the deviation (dev

CL

) of the operating point from any given control line can be calculated as:

If a control line (for example, the RTL) is to the right of the SLL, its bias and margin are negative, the operating point crosses that line before the compressor surges, and the deviation of the operating point from the control line is less than its deviation from the SLL.

If the control line is to the left of the SLL (the SOL), its bias and mar-gin are positive, the operating point crosses the control line only while the compressor is surging, and the deviation of the operating point from the control line exceeds its deviation from the SLL.

The

Control Line Characterizer

is typically defined as a constant [for example, f

4

(U

4

) = 1 for all U]. The control lines will then appear as shown in Figure 6-1, regardless of the argument or its value.

Disabling the

Control Line Argument

defines these distances as functions of the calculated flow measurement (usually

∆

P

o,c

). Giving that argument a value between one and eight (1 < fC 1 < 8) defines them as functions of the corresponding signal variable. However, the value 4 selects the Rotational Speed (see page 52), regardless of the source.

Surge ControlLine

The surge control line (SCL) defines the desired minimum distance between the operating point and surge limit line. The SCL is always to the right of the SLL. The surge control margin (SCM) is the dis-tance between those lines, which is calculated as:

where

b = surge control line bias (total b)

b

1

=

Initial Surge Control Bias

[SPEC:A b 1]

CR

D

= Derivative Response

CR

SO

= Safety On Response

The compressor’s deviation (DEV) from the SCL is:

The Antisurge PI Response increases the recycle rate when the operating point is to the left of this line (DEV < 0) and reduces it when that point is to the right of this line (DEV > 0).

The operating point’s proximity to this line is referred to as “S”, which will equal one when that point is on the SCL:

devCL 1 bias f4 U4( )⋅ Ss–+=

SCM b f4 U4( )⋅– b1 CRSO CRD+ +( ) f4 U4( )⋅–= =

DEV devSC 1 b f4 U4( )⋅ Ss––= =

S 1 DEV– Ss b f4 U4( )⋅+= =

September 2005 IM301 (6.1.3)


Recycle Trip Line The Recycle Trip line (RTL) defines an operating limit beyond which the Recycle Trip Response will ratchet the control valve open (that response is active when the operating point is to the left of this line).

The position of this line is defined relative to the surge limit line. The distance between them is the Recycle Trip margin (RTM), which is calculated as:

where

b1 = Initial Surge Control Bias [SPEC:A b 1]

CRSO = Safety On Response

RT = Recycle Trip Line Distance [SPEC:A RT]

The compressor’s deviation (devRT) from the RTL is:

As with all control lines, this distance is positive when the compres-sor is operating to the right of the RTL.

Safety On Line The Safety On line (SOL) defines an operating limit beyond which the compressor is assumed to be surging. The Safety On Response will increment the Cumulative Surge Count and increase the surge control line bias (total b) when the operating point moves to the left of this line.

This line is to the left of the surge limit line. The distance between them is the Safety On margin (SOM), which is calculated as:

where

SO =Safety On Line Distance [SPEC:A SO]

The compressor’s deviation (devSO) from the SOL is:

As with all control lines, this distance is positive when the compres-sor is operating to the right of the SOL.

RTM RT b1– CRSO–( ) f4 U4( )⋅=

devRT 1 RT b1– CRSO–( ) f4 U4( )⋅ Ss–+=

Note: The Recycle Trip Line Distance should be less than the Initial Surge Control Bias, so the RTL is always to the right of the SLL.

SOM SO f4 U4( )⋅=

devSO 1 SO f4 U4( )⋅ Ss–+=

September 2005 IM301 (6.1.3)


Tight Shut-OffLine

The tight shut-off line (TSL) defines the minimum SCL DEViation above which the Tight Shut Off Response (see page 101) can reduce the actuator control signal to zero (100 percent if reversed).

This line is always to the right of the SCL. The distance between them is the tight shut-off margin (TSM), which is calculated as:

where

d1 = Tight Shut-Off Line Distance [SPEC:A d 1]

The compressor’s deviation (devTS) from the TSL is:

As with all control lines, this distance is positive when the compres-sor is operating to the right of the TSL.

DerivativeResponse

If the Derivative Response [MODE:A fC 3] is enabled, this algorithm varies the surge control margin as a function of the rate at which the operating point is approaching the surge limit. That margin can thus be kept small (to minimize energy consumption) except during a rapid approach to surge.

The width of the surge control margin is governed by its total b coef-ficient, the third term of which is the derivative response:

where:

b3 = Maximum Derivative Response [SPEC:A b 3]

dSs/dt = time derivative of Ss (in percent of span/160 msec.),

r3 = CRD Dead-Zone Bias [PID:A r 3],in percent of span /160 msec.)

Td0 = CRD Time Constant [PID:A Td 0]

subject to the restriction that

The value calculated for this response is used only if it is larger than the value from the previous scan. Otherwise, it is ramped down at the General Ramp Rate [PID:A G]. This algorithm is suspended (that is, CRD is held constant) when the operating point is to the left of the surge limit line. It can and should be disabled if the flow mea-surement is excessively noisy.

As an aid to tuning this response, the Maximum Ss Derivative [PID:A Td 0 •] procedure can be used to display and optionally clear the highest detected rate of change for that variable.

TSM d1– f4 U4( )⋅=

devTS 1 b d1+( ) f4 U4( )⋅– Ss–=

b b1 CRSO CRD+ += CRD b3 Td0

dSs

dt---------- r3–

⋅ ⋅=

0 CRD b3≤ ≤

September 2005 IM301 (6.1.3)


Safety OnResponse

Configuration errors, process changes, compressor wear, or espe-cially severe disturbances can occasionally cause surge despite the actions of the Antisurge PI, Recycle Trip, and Derivative responses. When that happens, the Safety On response limits both the number of surges that do occur and the likelihood of their recurrence.

The width of the surge control margin is governed by its total b coef-ficient, the second term of which is the Safety On response:

where:

n = Cumulative Surge Count

b2,i = value of the Safety On Incremental Bias [SPEC:A b 2] when surge i was detected

Note that unless the b2 parameter is changed between surges:

The detection of a surge increments the surge count and moves the SCL to the right, thus increasing the distance between the operating point and surge limit.

Surge Detection If the Safety On Repeat Interval [SPEC:A A 5] is less than one sec-ond, the Surge Counters are incremented each time the operating point crosses to the left of the Safety On Line. Otherwise, they are repeatedly incremented at that interval for as long as the Safety On deviation is negative. If the Surge Detection Method [MODE:A fD 2] is set to zero, this is the only method used to detect surge.

If a non-zero Surge Detection Method is selected, the controller also monitors the rate of change of SV1 and/or SV2 (which are usually the unscaled flow and discharge pressure measurements) for indi-cations of surge. A surge detected by any of these methods will also trigger a Recycle Trip Response:

• If fD 2 is 1, a Safety On response is triggered when a rapid change in flow is detected followed by a rapid pressure change within the Pressure After Flow Time Lag [SPEC:A A 4], or a rapid pressure change is detected followed by a rapid change in flow within the Flow After Pressure Time Lag [SPEC:A A 2].

• If fD 2 is 2, this response is triggered when either a rapid change in flow or a rapid pressure change is detected.

• If fD 2 is 3, it is triggered only by a rapid change in flow.• If fD 2 is 4, it is triggered only by a rapid pressure change.

The derivative of SV1 is compared to the Flow Rate-of-Change Threshold [SPEC:A A 1], while that of SV2 is compared to the Pres-sure Rate-of-Change Threshold [SPEC:A A 3]. If one of these limits

b b1 CRSO CRD+ += CRSO b2 i,i 1=

n

∑=

CRSO n b2⋅=

September 2005 IM301 (6.1.3)


has a positive value, the surge counters are incremented when the corresponding variable’s rate-of-change exceeds that level. If it has a negative value, the counters are raised when the rate-of-change is more negative than the limit. In any case, surge detection is then suspended for the Safety On Repeat Interval [SPEC:A A 5].

After surge testing your compressor, the Maximum Flow Derivatives [SPEC:A A 1 •] and Maximum Pressure Derivatives [SPEC:A A 3 •] procedures can be used to determine appropriate thresholds (the values they report are dimensionally consistent with the correspond-ing parameters). These limits can also be calculated from a strip chart or similar data log. In that case, you should note that the units for these parameters are percent of scale per 160 milliseconds.

Surge Counters The controller can maintain two separate counts of the number of surges it has detected.

The cumulative surge count is the total number of surges that have been detected. The Safety On Response will increase the surge control margin whenever it is not zero. If the Surge Event Duration [COND:D CONST 1] is set to zero, this count will also trigger any Surge Event outputs whenever it equals or exceeds the Surge Event Threshold [COND:D CONST 0].

If the Surge Event Duration is not zero, the controller will also main-tain an event surge count:

• If this count is zero, detection of a surge will start an event timer.

• Each surge increments this count, which will trigger any Surge Event discrete outputs if it reaches the Surge Event Threshold.

• This count is set back to zero and all Surge Event relays are cleared when the timer has run for the Surge Event Duration.

Pressing the RESET SAFETY ON key, setting the D5 input, or clearing the Modbus SO coil resets both to zero, as will a shutdown if you enable the Safety On AutoReset [MODE:A fB 3].

Note:The “pressure” derivative is always based on the signal variable for analog input CH2. If ∆Pc Substitution is enabled for Pd [MODE:A SS 6 1 High], SV2 will be ∆Pc and surge detection will be based on the derivative of the unscaled ∆Pc signal.

Cumulative SurgeCount

Event Surge Count

September 2005 IM301 (6.1.3)


AntisurgeControl

Response

The antisurge control response (ACR) represents the intended recycle flow. Because raising that flow is often the best available solution for more than one protective or limiting control objective, ACR is calculated by adding the highest proportional, integral, and Recycle Trip responses of several control loops.

For example, opening a recycle valve may not only be the best way to prevent surge, but also the best way to limit the maximum system pressure. In other cases, only one recycle valve may be installed on a multi-section compressor, so the recycle flow must be kept high enough to prevent surge in any section of that compressor.

PI and RT SignalSelection

The ACR is calculated by adding loop decoupling and primary capacity (load-sharing applications only) control responses to selected proportional, integral, and Recycle Trip responses:

where:

CRI = accumulated integral response

= previously accumulated integral

∆CRI,max = largest integral response from among the Antisurge PI Response and Pressure Limiting loops, any Auxiliary Limiting or Performance Override Performance Con-trollers, or any Valve Sharing (see page 91) controllers

∆CRLD = Loop Decoupling response

∆CRPC = Primary Capacity Control (see page 92) response

CRP,max = the largest proportional response from any of the sources listed for ∆CRI,max

CRRT,max = the largest of its own Recycle Trip Response or those of any designated Valve Sharing Antisurge Controllers

By selecting the highest of the indicated PI and RT responses, the controller assures that the recycle flow rate will be sufficient to meet all of their protective and limiting control objectives. In order to pre-vent any of those control loops from experiencing integral windup, the Antisurge Controller will notify them if it is being manually oper-ated or if the control valve has been fully opened. Any closure of the recycle valve in response to a declining POC signal will proceed at a maximum rate that is half of the General Ramp Rate [PID:A G].

Note:These control responses assume the compressor has a signal-to-open recycle valve. The resulting control signal is adapted to the actual valve by setting the Recycle Valve Direction [MODE:A REV].

ACR CRP max, CRI CRRT max,+ +=

CRI CRI– CRI max,∆ CRLD∆ CRPC∆+ + +=

CRI–

September 2005 IM301 (6.1.3)


Figure 6-2 Dead-zone error (e) as a function of the DEViation

General PIAlgorithm

The Antisurge Controller uses the following general PI algorithm to calculate proportional (CRP) and integral (∆CRI) responses from the deviation of each control variable from its set point:

where

∆t = scan time in seconds

Kr = reset rate [PID:A Kr #, in repeats/minute]

PB = proportional band [PID:A PB #]

The PB and Kr coefficients are set independently for each control function using this algorithm.

Dead Zone The Antisurge Controller can be configured to ignore minor devia-tions of the operating point from the surge control line (SCL) by setting its DEV Dead-Zone Bias [PID:A r 1].

The error for the antisurge PI loop is then calculated by adding or subtracting that dead-zone bias from the DEViation (see Figure 6-2). This creates a dead zone around the SCL, the total width of which is twice the value of r 1.

This dead zone can be disabled by setting r 1 to zero. Note that r 1 should be less than the Recycle Trip Line Distance [SPEC:A RT].

DEV

e

r1

e = DEV + r1 if DEV ≤ –r1

DEV – r1 if DEV ≥ –r10 if –r1 ≤ DEV ≤ r1

CRP100PB---------- e⋅= CRI∆ 100

PB---------- Kr

60------ e t∆⋅ ⋅ ⋅=,

September 2005 IM301 (6.1.3)


Antisurge PIResponse

During each scan, the controller uses its general PI control algo-rithm to calculate separate proportional and integral responses to the operating point’s deviation from the Surge Control Line (SCL):

• When that deviation is positive (DEV > 0), the antisurge PI response will gradually close the recycle valve to minimize unnecessary recycling.

• When that deviation is negative (DEV < 0), the PI response will open the recycle valve as needed to restore the desired surge control margin.

In other words, the antisurge PI response is used to counter routine disturbances by maintaining the operating point as close as possible to the SCL. This loop is configured by setting the

DEV Proportional Band

[PID:A PB 1],

DEV Reset Rate

[PID:A Kr 1], and

DEV Dead-Zone Bias

[PID:A r 1]. Its error is then calculated from the DEViation and dead-zone bias:

The output clamps prevent integral windup when the compressor is operating to the right of the surge control line with the control valve fully closed.

A ramping function is used to prevent sudden output changes when switching from manual to automatic surge protection. Under such circumstances, the controller sets the effective value of its DEVia-tion to zero and ramps it to the value calculated from the analog inputs at half the rate set by the

General Ramp Rate

[PID:A G].

e 0.512 DEV r1±( )⋅=

September 2005 IM301 (6.1.3)


Figure 6-3 Typical Recycle Trip response

Recycle TripResponse

The Recycle Trip response protects against disturbances that are too large or fast to be countered by the PI and derivative responses. In essence, it defines a maximum overshoot for S

s

. If that limit is exceeded, the Recycle Trip response quickly ratchets the recycle valve open, then waits for the Antisurge PI Response to catch up.

This response is triggered when the operating point moves to the left of the RTL (see Recycle Trip Line on page 73) or the SV1 or SV2 rate-of-change indicates a surge has occurred (see Surge Detection on page 75). The controller will then step the recycle valve open as shown on Figure 6-3.

If the

Derivative Recycle Trip

[MODE:A fC 4] is enabled, the size of each step (

∆

RT) is calculated as:

where:

C

0

=

Recycle Trip Gain

[SPEC:A C 0],

C

1

=

Maximum Recycle Trip Step Size

[SPEC:A C 1],

dev

RT

= Recycle Trip deviation (negative when operating to the left of the RTL),

dS

s

/dt = derivative of S

s

with respect to time (in percent of span/160 msec.), and

Td

1

=

Recycle Trip Time Constant

[PID:A Td 1],

The size of each step is subject to the restriction:

Slow Closing

Rec

ycle

Trip

Res

pons

e

Time

QuickOpening

CRRT∆ C1 Td1

dSs

dt----------⋅ C0 devRT⋅–

⋅=

0 CRRT∆ C1≤ ≤

September 2005 IM301 (6.1.3)


These step changes are added at intervals set by the Recycle Trip Repeat Interval [SPEC:A C 2] as long as the operating point is to the left of the RTL and the operating point is moving toward the surge limit (that is, when dSs /dt is positive).

If the approach to surge is rapid, the derivative term (Td1 · dSs/dt) usually restores a safe operating point before the proportional term (C0 · devRT) becomes significant. On the other hand, if the approach to surge is slow, the derivative term might never become significant. In such cases, the proportional term would grow until the resulting Recycle Trip response was large enough to move the operating point back to the SCL.

As an aid to tuning this response, the Maximum Ss Derivative [PID:A Td 0 •] procedure can be used to display and optionally clear the highest detected rate of change for that variable. In addition, the Force Recycle Trip [MODE TEST] test can be used to evaluate your compressor’s response to a Recycle Trip control action.

In applications where the flow measurement is excessively noisy, the Derivative Recycle Trip should be disabled [fC 4 Off]. This response will then generate steps of constant magnitude C1 as long as the operating point is to the left of the RTL.

When the operating point returns to the right of the RTL, the accu-mulated Recycle Trip control response will decay exponentially at the Recycle Trip Decay Rate [SPEC:A TL]. If the operating point reaches the SCL during this decay, the PI response will increase to prevent any closer approach to surge.

The front-panel RT LED will light and any discrete outputs assigned the RT function will be set when the operating point crosses the RTL (when devRT becomes negative). If the controller is operating auto-matically, the RT LED will remain lit until the Recycle Trip response decays to zero, but any RT relays will be cleared as soon as the operating point moves back to the right of the RTL. If the controller is being manually operated, all RT indicators remain set until a positive devRT is restored.

September 2005 IM301 (6.1.3)


Pressure Limiting The Antisurge Controller can limit the maximum discharge pressure and minimum suction pressure by increasing the recycle flow:

• If Discharge Pressure Limiting [MODE:A MVAR 2] is enabled, that response is calculated by applying the Pd Proportional Band [PID:A PB 2] and Pd Reset Rate [PID:A Kr 2] to the devia-tion of Pd above the Maximum Discharge Pressure [COND:A SP 2]:

• If Suction Pressure Limiting [MODE:A MVAR 3] is enabled, that response is calculated by applying the Ps Proportional Band [PID:A PB 3] and Ps Reset Rate [PID:A Kr 3] to the deviation of Ps below the Minimum Suction Pressure [COND:A SP 3]:

If either pressure is beyond its control threshold, the DEV and ALT readouts will display it and its set point when the DISPLAY LIMIT key is pressed. Each loop’s readouts use the corresponding mea-sured variable scaling unless ∆Pc Substitution [MODE:A SS 6 1] is enabled for that pressure, in which the calculated pressure is limited and its limiting readouts are displayed in percent.

By including these proportional and integral responses (CRP and ∆CRI) in its PI and RT Signal Selection, the controller keeps the recycle rate high enough to satisfy the limiting control objectives without compromising surge protection.

In fA 01 and 02, which use CH2 as a differential pressure input (∆Pc), the PV2 high-limiting loop applies to that pressure rise. The PV3 loop is available only in software revision 756-002 or higher, and applies to whatever variable is connected to analog input CH3.

If your process has other variables that can be limited by increasing the recycle or blowoff flow rate, a Series 3 Plus Performance Con-troller can be used to effectively add another limiting variable to the Antisurge Controller (see Auxiliary Limiting on page 83 and Perfor-mance Override on page 83).

Pressure LimitScaling

When setting the pressure limiting thresholds and PI coefficients, keep in mind that they are usually percentages of a common maxi-mum absolute pressure.

For example, assume that the discharge pressure is measured by a 0 to 500 psig sensor and the suction pressure by a 0 to 50 psia sensor. If you have scaled PV2 and PV3 relative to their common absolute maximum, a discharge pressure limit of 250 psig would be entered as 52.0% (264.7 psia / 514.7 psia). A suction pressure limit of 20 psia would be entered as 3.9 percent (20 psia / 514.7 psia).

e Pd SP2–=

e SP3 Ps–=

September 2005 IM301 (6.1.3)


Auxiliary Limiting The recycle valve will sometimes be the most appropriate control element for a limiting variable other than the discharge and suction pressures. As described in the Auxiliary Limiting Control section in Chapter 6 of IM302, such limiting loops can be implemented by con-figuring a Performance Controller to submit its PD and ∆I responses to an Antisurge Controller’s PI and RT Signal Selection algorithm.

That Antisurge Controller is configured to accept them by enabling its Valve Sharing Companion [MODE:A SS 1 #] parameter that cor-responds to the Performance Controller’s Controller ID Number. To avoid integral windup, the Performance Controller suspends its inte-gral control action when the Antisurge Controller is being manually operated or its control valve is fully open.

PerformanceOverride

Enabling Performance Override Control [MODE:A SS 3] configures an Antisurge Controller to include a Performance Controller POC response (received via Port 2) in its PI and RT Signal Selection. This would increase the recycle rate when needed to limit that con-troller’s performance override control variable, as described in the Performance Override Response section in Chapter 6 of IM302.

Loop Decoupling The potentially destabilizing effects that could result from interac-tions between an antisurge control response and its compressor’s performance and other antisurge control loops can be counteracted by the loop decoupling algorithm, as described in the Loop Decou-pling section in Chapter 6 of IM302.

To decouple an Antisurge Controller from a specified companion, enable theDecoupling Controller [MODE:A SS 0 #] parameter corre-sponding to its Controller ID Number and assign an appropriate value to the corresponding Decoupling Gain [COND:A M #]. Loop decoupling can be completely disabled by setting all eight SS 0 parameters to Off, which can be most easily accomplished by enter-ing the key sequence MODE:A SS 0 0 from the Engineering Panel.

Assigning a non-zero Valve-Sharing Master ID [MODE:A SS 2] enables secondary Valve Sharing (see page 91). In that case, the loop-decoupling algorithm is not executed (even if it is enabled) and all MODE:A SS 0 parameters are automatically disabled when the controller is reset (see MODE TEST 6 on page 146).

Note: The proportional output reported by a Performance Controller includes its derivative response (CRP + CRD).

Note: The loop-decoupling response can only be positive, so it will never decrease the recycle flow rate.

September 2005 IM301 (6.1.3)


September 2005 IM301 (6.1.3)



Chapter 7 Multi-Compressor ProtectionThis chapter describes the additional features used to protect multi-section and networked compressors from surge.

Figure 7-1 Imaginary orifice coefficients and equivalent flow measurements

MultisectionCompressors

A multi-section compressor has one or more ports between the suc-tion and discharge where sidestreams can be withdrawn or injected. This generally requires the calculation of Equivalent Flow Measure-ments for all but the first or last section. If a single recycle valve is used to protect more than one section of the compressor, Valve Sharing should be employed to ensure adequate protection under changing process conditions.

Equivalent FlowMeasurements

We use the term equivalent flow measurement to mean the differen-tial pressure drop that would be measured by an orifice plate in a location where one is not and generally can not be installed. The equations used to calculate these measurements from suction, dis-charge, and sidestream flow measurements are derived from mass and energy balances across the relevant compressor sections or sidestream junctions.

The required calculations utilize the following equation for the mass flow through an orifice plate or similar flow-measuring element:

where:

Co = constant orifice flow coefficient

∆Po = pressure drop across the orifice plate

M = molecular weight

P = absolute pressure

T = absolute temperature

Z = compressibility

Co,s2 , ∆Po,s2 ∆Po,d2

Co,d2∆Po,s1 Co,ss , ∆Po,ss

Suction Flow Measured Discharge Flow Measured

Co,s2 , ∆Po,s2 Co,d1 , ∆Po,d1 ∆Po,d2

Co,s1 Co,d2 Co,d1 , ∆Po,d1

Co,ss , ∆Po,ss ∆Po,s1

Co,s1

W2 Co M P Po∆⋅ ⋅ Z T⋅( )⁄⋅=

September 2005 IM301 (6.1.3)

86 Chapter 7: Multi-Compressor Protection

Reported Flow Except as noted below, any Antisurge Controller with Series Load Variable [MODE:A fC 9] disabled reports its Calculated Flow Mea-surement (see page 54) to its companion controllers via Port 1.

If fA Mode 31 or 33 is selected, the reported flow is calculated as:

where:

∆Po,c = Calculated Flow Measurement

∆Po,r = reported flow measurement

f2(Rc) = Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #]

Rc = Compression Ratio (Pd/Ps)

If ∆Po,c and the needed ∆Po,r correspond to the same location, f2 can be defined as a constant:

If not, the required function can be derived from a steady-state (equal molecular weight) mass balance across the compressor:

From the thermodynamic principles governing polytropic compres-sion, it can be shown that:

Values for the Reported Flow Characterizer can be calculated from the relationship on the right, using an imaginary orifice constant that yields an acceptable range for the reported flow given the expected ranges of the measured flow and compression ratio.

All fA Modes between 61 and 69, inclusive, report squared Mass Flow Rates (see page 58):

where:

β5 = Mass Flow Coefficient [COND:A β 5]

∆Po,c = Calculated Flow Measurement

If one of these modes is used with another controller using fA 34 or 35, configure it to report its rescaled ∆Po,c by selecting the same input for both Pc and Tc.

Po r,∆ Po c,∆ f2 Rc( )⋅=

Po r,∆ Po c,∆= f2 Rc( ) 1=

Co s, Ps Po s,∆ ZsTs⁄ Co d, Pd Po d,∆ ZdTd⁄=

Po s,∆Po d,∆

---------------Co d, Zs

Co s, Zd------------------

Pd

Ps------

Ts

Td------

=

Td

Ts------

Pd

Ps------

σRc

σ= =

Po s,∆Po d,∆

---------------Co d, Zs

Co s, Zd------------------ Rc

1 σ–=

W2 β5 Po c,∆ Pc Tc⁄⋅⋅=

September 2005 IM301 (6.1.3)


Upstream SectionFlow Known

If the compressor’s suction flow and the sidestream flow into the second section are measured (as shown in the left panel of Figure 7-1), the second section’s equivalent suction flow measurement can be calculated from the equivalent discharge pressure of the first:

If the sidestream flowed out of rather than into the compressor, the above equation would be an equality with a negative third term.

Because surge occurs under minimum flow conditions, maximum protection can be obtained by calculating proximity to surge from the minimum flow given by the right side of the above equation. Thus, fA 34 computes an equivalent suction flow measurement as:

where:

C3 = Sidestream Flow Coefficient [SPEC:A C 3]

C4 = Main Flow Coefficient [SPEC:A C 4]

C5 = Combined Flow Coefficient [SPEC:A C 5]

= equivalent upstream section discharge flow

= Reported Flow measurement from the Adjacent Sec-tion Controller [MODE:A SS 5]

∆Po,s = equivalent suction flow measurement

∆Po,ss = sidestream flow measurement (PV1)

f2() = Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #]

Ps = suction pressure of this section

= upstream section suction pressure

Equations for the flow coefficient parameters can be derived by comparing the above equations:

For a sidestream entering the compressor, C5 would be positive and the imaginary orifice constant (Co,s2) can be determined by setting both component flow measurements to one. Assuming the equiva-lent suction flow measurement should then be one as well:

Po s2,∆Co ss, Po ss,∆ Co d1, Po d1,∆ 2 Co ss, Co d1, Po ss,∆ Po d1,∆+ +

Co s2,------------------------------------------------------------------------------------------------------------------------------------------------------≥

Po s,∆ C3 Po ss,∆ C4 P∆ o d,– C5 Po ss,∆ P∆ o d,

–+ +=

P∆ o d,– P∆ o r,

– f2 Ps Ps–⁄( )⋅=

P∆ o d,–

P∆ o r,–

Ps–

C3 Co ss, Co s2,⁄= C4 Co 1d, Co 2s,⁄= C5 2 C3C4±=

Po s2,∆ 1 C3 C4 2 C3C4+ += =

Co s2, Co ss, Co d1, 2 Co ss, Co d1,+ +=

September 2005 IM301 (6.1.3)


Figure 7-2 Calculating equivalent flows when suction flow is measured

If the sidestream flowed out of rather than into the compressor, C5 should be negative and the imaginary orifice constant should have the same value as that for the preceding compressor section:

based on the assumption that ∆Po,s2 should equal ∆Po,d1 when the sidestream outflow is zero.

As shown in Figure 7-2, the Antisurge Controller for the first section of a multisection compressor should be configured to report its equivalent discharge flow measurement.

The Antisurge Controller for the second section can then use fA Mode 34 with its f2 characterizer defined as unity (equal to one for all values of its argument). Thus, it would not require an input signal for the first section’s suction pressure, and would report its equiva-lent suction flow measurement.

The Antisurge Controller for the third section could also use fA Mode 34, but would have to use its own f2 characterizer to calculate the second section’s equivalent discharge flow measurement. Thus, it would need an input signal for the second section suction pressure.

UIC

PT PTFT

1UIC

PT

3UIC

PT

2Port 1

FT FT

Port 1

fA Mode: 31 or 33

Po r,∆ Po d,∆∝

Po c,∆ Po s,∆=

f2 X( ) Xσ 1–∝

fA Mode: 34

Po r,∆ Po s,∆=

Po c,∆ Po s,∆=

f2 X( ) 1=

fA Mode: 34

Po r,∆ Po s,∆∝

Po c,∆ Po s,∆=

f2 X( ) Xσ2 1–

∝

Co s2, Co d1,=

September 2005 IM301 (6.1.3)


Downstream SectionFlow Known

If the compressor’s discharge flow and the sidestream flow into the last section are measured (as shown in the right panel of Figure 7-1), the next-to-last section’s equivalent discharge flow measure-ment can be calculated from the equivalent suction flow of the last:

If the sidestream flowed out of rather than into the compressor, this equation would be an equality with a positive third term.

Because surge occurs under minimum flow conditions, maximum protection can be obtained by using the minimum flow given by the right side of the above equation. Thus, fA 35 computes proximity to surge from its own reported flow, which is calculated as:

where:




f2() = Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #]

∆Po,d = this section’s equivalent discharge flow measurement

∆Po,r = this section’s Reported Flow measurement

= reported downstream flow measurement from the Adjacent Section Controller [MODE:A SS 5]

∆Po,ss = sidestream flow measurement (PV1)

Rc = this section’s compression ratio

Equations for the flow coefficient parameters can be derived by comparing the above equations:

For a sidestream entering the compressor, C5 should be negative and the imaginary orifice constant should have the same value as that for the downstream compressor section:

based on the assumption that ∆Po,d1 should equal ∆Po,s2 when the sidestream inflow is zero.

For a sidestream leaving the compressor, C5 should be positive and the imaginary orifice constant can be determined by setting both

Po d1,∆Co ss, Po ss,∆ Co s2, Po s2,∆ 2 Co ss, Co s2, Po ss,∆ Po s2,∆–+

Co d1,-----------------------------------------------------------------------------------------------------------------------------------------------------≥

P∆ o r, P∆ o d, f2 Rc( )⋅=

Po d,∆ C3 Po ss,∆ C4 P∆ o r,+ C5 Po ss,∆ P∆ o r,

+⋅+ +=

P∆ o r,+

C3 Co ss, Co d1,⁄= C4 Co s2, Co d1,⁄= C5 2 C3C4±=

Co d1, Co s2,=

September 2005 IM301 (6.1.3)


Figure 7-3 Calculating equivalent flows when discharge flow is measured

component flow measurements to one. Assuming the equivalent discharge flow measurement should then be one:

As shown in Figure 7-3, the Antisurge Controller for the last section of a multisection compressor should be configured to report its equivalent suction flow measurement.

If there is only one upstream section with no flow measurement, its Antisurge Controller can use fA Mode 35 with its f2 characterizer defined as unity (equal to one for all argument values), so proximity to surge is calculated from its discharge flow measurement.

If there are two upstream sections that lack flow measurements, both of their Antisurge Controllers can use fA Mode 35. However, the next-to-last section’s controller must use and report its suction flow measurement to the second-to-last section’s controller:

The second-to-last section can be configured to use and report its discharge flow by defining its f2 characterizer as unity:

UIC

PT PT

1UIC

PT

3UIC

PT

2Port 1

FT FT

Port 1

fA Mode: 35

Po r,∆ Po d,∆∝

Po c,∆ Po r,∆=

f2 X( ) 1=

fA Mode: 35


Po c,∆ Po r,∆=

f2 X( ) X1 σ–∝

fA Mode: 31 or 33


Po c,∆ Po d,∆=

f2 X( ) X1 σ–∝

FT

Po d1,∆ 1 C3 C4 2 C3C4+ += =

Co d1, Co ss, Co s2, 2 Co ss, Co s2,+ +=

Po r, Po s,∆ Po d,∆ Rc1 σ–⋅= =

f2 Rc( ) Rc1 σ–

=

Po r, Po d,∆= f2 Rc( ) 1=

September 2005 IM301 (6.1.3)


Valve Sharing Each section of a compressor should be equipped with its own anti-surge controller even if there is only one recycle path and control valve for the entire machine. In such cases, several Antisurge Con-trollers can be configured to use Port 1 serial communications to share a single valve (see Figure 1-3).

In such applications, the response of a valve-sharing master control-ler is used to manipulate the recycle valve. All other, valve-sharing companion controllers submit their control responses to the master. The master protects the entire compressor from surge by selecting the highest of several PI and RT responses (see PI and RT Signal Selection on page 77).

To configure an Antisurge Controller as a valve-sharing master, dis-able the Valve-Sharing Master ID [MODE:A SS 2] and any Valve Sharing Companion [MODE:A SS 1 #] parameters that do not correspond to valve-sharing companion Controller ID Numbers. To configure it as a valve-sharing companion, set the Valve-Sharing Master ID equal to the master’s Controller ID Number. To disable this feature, set SS 2 and all SS 1 parameters to Off.

Every valve-sharing controller must be configured to select its Shut-down state when its compressor is stopped (see Valve Sharing Shutdowns on page 104). If each controller’s operating state selec-tion is so configured, the system will manipulate the recycle valve as needed to protect the compressors that are running.

The actuator control signals of the valve-sharing companions are not displayed on their front-panel OUT readouts, nor can they be manipulated manually or via computer control. However, their Mod-bus Out Display input registers will track the master’s actuator control signal.

To avoid integral windup, valve-sharing companions suspend their integral responses when the master is being manually operated or the recycle valve is fully open. On the other hand, a valve-sharing companion will not suspend its integral control response simply because its output is not selected by the master. If the selected response fails to restore an acceptable DEV to any given compres-sor section, its controller should and will continue integrating until its response is chosen.

September 2005 IM301 (6.1.3)


NetworkedCompressors

Networks of Series 3 Plus Controllers can be used to regulate the capacity and maximize the efficiency of several compressors oper-ating in parallel or in series, as described in Chapter 7 of IM302.

In such networks, each compressor’s Antisurge Controller can not only participate in the Performance Override (see page 83) and Primary Capacity Control, but also calculates the proximity-to-surge related variables required by the Load Balancing algorithm.

In parallel compressor networks, the Antisurge Controllers can also be configured for Recycle Balancing (which occurs automatically in a series network). Such a system might also include an Antisurge Controller configured for Cold-Recycle Control.

Figure 7-4 Setting Primary Capacity Control Thresholds


As described in the Primary Capacity Control section in Chapter 7 of IM302, a load-sharing system’s primary capacity control objective is met by varying the antisurge and performance control responses of its Load-Sharing, Unit, and Antisurge Controllers as functions of the station control signal.

The primary capacity control response (∆CRPC) that is added to the Antisurge Control Response (see page 77) is calculated as:

where:

ß3,A = Recycling Threshold [COND:A β 3]

M0,A = Recycling Gain [COND:A M 0]

S = S proximity-to-surge variable selected by the specified Load-Sharing Controller [MODE:A SS 4]

∆SCS = station control signal change since previous scan

If configured as described in the above-referenced section of IM302, this response (and the resulting recycle rate) will rise only if the selected S exceeds the Recycling Threshold. The Station Controller

station controlresponse can

β3 (

A)

S

β3 (

P)

∆SC

S

0 2

increase recycle

S =

1

S

∆SC

S

0 2

S =

1

station control response

can throttlecompressor

CRPC∆ M0 A, SCS∆ fA S( )⋅ ⋅=

fA S( ) 1 if S β3 A,> and M0 A, SCS∆⋅ 0>

0 if S β3 A,< or M0 A, SCS∆⋅ 0≤

=

September 2005 IM301 (6.1.3)


can then vary the outputs of the Antisurge Controllers in a way that minimizes recycling without compromising surge protection.

Load Balancing As explained in the Load Balancing section in Chapter 7 of IM302, the CV1 control loops of the Load-Sharing Controllers distribute the total load by equalizing an appropriate load-balancing variable.

If Series Load Variable [MODE:A fC 9] is enabled, an Antisurge Controller will calculate the following measure (L) of the total load, and report its value over Port 1 instead of a Reported Flow:

where:

A = domain selector (0 ≤ A ≤ 1) calculated by the Station Controller

CVb = Load Balancing Variable [MODE:A fD 9]

f2A() = Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #]

f2D() = Recycle Flow Characterizer [COND:D f(X) 2 # and X 2 #]

f6() = Balancing Variable Characterizer [COND:A f(X) 6 # and X 6 #]

IVP = Intended Valve Position (see page 98)

Pd = Discharge Pressure (see page 51)

Rc = Compression Ratio (see page 51)

S = proximity to the Surge Control Line (see page 72)

Td = Discharge Temperature (see page 51)

Wr = recycle flow rate

The Load Balancing Variable can be any single input process vari-able [1 ≤ fD 9 ≤ 8]. Setting it to 4 selects the Rotational Speed (see page 52), regardless of its source. Disabling that parameter [fD 9 = Off] selects the Compression Ratio (Rc, in percent of ten).

For parallel compressors, the Series Load Variable [MODE:A fC 9] calculation should be disabled. Load balancing will then equalize the compressors’ proximity to surge.

LA f6 CVb( )⋅

10----------------------------

1 A–( ) Suser⋅2

------------------------------------+=

Suser S 1 Wr+( )⋅=

Wr f2D IVP( ) f2A Rc( )Pd

100 Td⋅-------------------------⋅ ⋅=

Note: The Station Controller can be configured such that A is always 0 or always 1, thus making L exclusively a function of either CVb or Suser.

September 2005 IM301 (6.1.3)


RecycleBalancing

If recycling becomes necessary, the load-balancing algorithm for parallel compressors might not equalize their recycle flow rates. As explained in the Recycle Balancing section in Chapter 7 of IM302, either Port 1 Balancing or Port 2 Balancing can then be used to equalize the recycle rates.

The Port 2 approach will be used if both methods are configured. If neither is enabled, the recycle flow rates of a parallel compressor network may differ.

Port 1 Balancing Port 1 recycle balancing equalizes the combined PI and RT signals of a group of Antisurge Controllers identified by each others’ Valve Sharing Companion [MODE:A SS 1 #] and Recycle Balancing Con-troller [MODE:A SS 7 #] parameters. For example, to balance this controller’s responses with those of a companion with Controller ID Number 3, you must enable both SS 1-3 and SS 7-3.

If their PI+RT signals diverge while the compressors are moving away from surge (that is, while the valves are closing), the controller with the highest signal will close its valve at half the General Ramp Rate [PID:A G]. All other controllers slow the rate at which they are closing their valves by holding their integral responses constant. The furthest open valve will thus catch up by closing more quickly than the others.

If those signals diverge while the compressors are moving toward surge (that is, while the valves are opening), the controller with the highest signal (presumably closest to surging) will operate normally (so adequate surge protection is maintained) while the others open their valves at the General Ramp Rate. This opens the more closed valves at a higher rate until they catch up with the most open.

Port 2 Balancing Under Port 2 recycle balancing, each Load-Sharing Controller monitors the DEViation, actuator control signal, and operating state of its companion Antisurge Controllers. It picks the highest control signal from among those operating automatically in their Run states with DEVs less than 0.1, and reports it to the Station Controller.

The Station Controller, in turn, selects the highest antisurge control signal reported by any Load-Sharing Controller. It then broadcasts that value back to all of the Antisurge Controllers.

Each Antisurge Controller with Port 2 Recycle Balancing [MODE:A SS HIGH] enabled will then raise its control response at one half its General Ramp Rate [PID:A G] if its control signal is more than two percent below that broadcast by the Station Controller.

September 2005 IM301 (6.1.3)


Cold-RecycleControl

Parallel networks sometimes include a single station recycle line in addition to an individual unit-recycle line for each compressor (see Figure 1-6). If the former is temperature controlled and the latter are not, they can also be called cold- and hot-recycle lines. As explained in the Cold-Recycle Control section in Chapter 7 of IM302, the cold or station recycle flow can be controlled by either an Antisurge or Performance Controller.

An Antisurge Controller is adapted to this application by selecting fA mode 00. It then calculates its surge control line deviation from the lowest DEViation (DEVmin) reported by any specified Valve Sharing Companion [MODE:A SS 1 #]:

• For small networks, the controller uses Port 1 to communicate directly with Antisurge Controllers specified by enabling the SS 1 parameters corresponding to their Controller ID Numbers.

• For large networks, the controller gets DEVmin from the Station Controller, which selects the lowest DEV calculated by any of its Load-Sharing Controllers’ companion Antisurge Controllers. The Cold-Recycle and Station Controllers should be connected by an isolated Port 1 network, and only the SS 1 parameter cor-responding to the Station Controller’s ID should be enabled.

In either case, the Cold Recycle Controller calculates its DEViation by adding its own surge control margin to the selected DEVmin:

Note that this margin is, in effect, added to that of the companion controller reporting DEVmin. In most cases, you would define this added margin as a constant by:

• setting the Initial Surge Control Bias [SPEC:A b 1] equal to the desired constant,

• configuring the Control Line Characterizer [COND:A f(X) 4 # and X 4 #] to always return a value of one. The Control Line Argument [MODE:A fC 1] can then be given any value,

• zeroing the Safety On Incremental Bias [SPEC:A b 2], and

• zeroing the Maximum Derivative Response [SPEC:A b 3].

This added margin assures that a Cold-Recycle Antisurge Controller will reach its surge control line and begin recycling before any hot-recycle Antisurge Controller. Except in the case of a rapid or large disturbance, opening the cold-recycle valve will provide enough extra flow to prevent surge without opening any hot-recycle valves.

DEV DEVmin b f4 Z( )⋅–=

DEVmin CRSO CRD+( ) f4 Z( )⋅–=

September 2005 IM301 (6.1.3)


September 2005 IM301 (6.1.3)



Chapter 8 Output VariablesThis chapter tells how the valve position and actuator control signal are derived from the antisurge control response.

Figure 8-1 Output transformations

AnalogInputs

Antisurge Control Response(Intended Recycle Flow)

Output Reverse

or

Output Clamps


Tight Shut Off

Actuator Control Signal

Intended Valve Position

OUT Readout

Output Tracking

Manual


Valve FlowCharacterizer

September 2005 IM301 (6.1.3)

98 Chapter 8: Output Variables

Figure 8-2 Valve flow characterization

Intended ValvePosition

As shown in Figure 8-1, the intended valve position is calculated by applying Valve Flow Characterization to the Antisurge Control Response (see page 77), which represents the intended recycle or blow-off flow rate.

Valve FlowCharacterization

If your control valve exhibits inherently non-linear flow, you can ren-der its actual flow linear with respect to the intended flow rate by selecting an appropriate Valve Flow Characterizer [MODE:A fC 8]. Figure 8-2 illustrates the relationship between the intended recycle flow and intended valve position for each pre-defined characterizer:

fC 8 High: for quick-opening valves

fC 8 Low: for equal-percentage valves

fC 8 Off: for linear flow valves.

For quick-opening valves, the flow is assumed to be proportional to the square root of the fractional valve opening. Thus, when fC 8 is HIGH, the control signal is obtained by squaring the intended flow rate calculated by the control algorithms. If the intended flow is 50 percent (1/2), for example, the valve position would be 25 percent [(1/2)2 = 1/4]. For a signal-to-open valve with a 4 to 20 mA actuator, the output signal would be 8 mA.

Conversely, the flow rate for an equal-percentage valve is assumed to be proportional to the square of the fractional valve opening. Thus, when fC 8 is LOW, the control signal is obtained by taking the square root of the intended flow rate. For example, if the intended flow is 25 percent (1/4), the valve position would be 50 percent (1/2). For a signal-to-open valve with a 4 to 20 mA actuator, the output sig-nal would be 12 mA.

Mode fC 8 Off

Intended Flow Rate

Inte

nded

Val

ve P

ositi

on

0 1

Mode fC 8 Low

(quick-opening valve)(lin

ear valve)

(equal-percentage valve)

Mode fC 8 High

1

September 2005 IM301 (6.1.3)


ActuatorControl Signal

The actuator control signal (ACS) is the intended value of the analog signal used to position the final control element. As shown in Figure 8-1, it is calculated by applying the following transformations to the Intended Valve Position:

• Valve Dead Band Compensation adapts the controller to valves with worn actuator linkages.

• The Output Clamps limit the control signal’s range. The Remote Low Output Clamp allows a companion device to increase the low clamp (and thus the minimum recycle rate).

• The Tight Shut Off Response fully closes the control valve when it is at its low clamp position and the operating point is safely to the right of the surge control line.

• Output Reverse adapts the controller to a signal to-close valve.

• Output Tracking keeps the control signal equal to a specified analog input whenever the D4 discrete input is asserted.

Figure 8-3 Valve dead band compensation


Due to wear or design imperfections, a control valve might exhibit a positioning dead band that must be overcome when the control action reverses direction. The Antisurge Controller can counter this effect by adding or subtracting a Valve Dead-Band Bias [COND:A OUT 1] to the intended valve position. Because this bias is added when the control response is rising and subtracted when it is falling, a change in the control response’s direction produces a step change in the control signal equal to twice this bias (see Figure 8-3).

For best results, this feature should be used in conjunction with an antisurge loop Dead Zone (see page 78).

Valve dead-band compensation can be disabled by assigning its bias a value of zero.

OUT 1

Actuator Contro

l Signal

Intended Valve PositionS

igna

l

Time

Note: This feature will not move the ACS beyond either output clamp.

September 2005 IM301 (6.1.3)


Output Clamps The range of the actuator control signal is set by the Recycle Low Clamp [COND:A OUT LOW] and Recycle High Clamp [COND:A OUT HIGH]. These clamps are implemented by raising or lowering the accumulated integral response (see General PI Algorithm on page 78) as needed to keep the ACS within the specified range.

These clamps are entered as the minimum and maximum intended valve positions, which correspond to the highest and lowest values that would be displayed on the front-panel OUT readout. That is, the output will be constrained such that OUT never displays a number less than OUT LOW or higher than OUT HIGH.

Any Valve Open relays will be triggered whenever the actuator con-trol signal is greater than the low output clamp.

Remote Low OutputClamp

The Antisurge Controller can be configured to use the output of another controller as its low output clamp when that signal is less than the low output clamp. This prevents the Antisurge Controller from reducing its output below that of the remote device, without risking integral windup or restricting its ability to open the valve as needed to prevent surge. In contrast to Output Tracking, this feature holds the recycle valve open far enough to satisfy both controllers.

To utilize this feature, connect the output of the remote device to any otherwise unused analog input and set the Remote Low Output Clamp [MODE:A fE 4] equal to that input’s channel number. For example, if you connect the output of the remote device to CH7, fE 4 must be set to 7. Setting fE 4 to zero (Off) disables this feature.

Unless the specified input fails, the low output clamp will then be the greater of its signal variable or the Recycle Low Clamp parameter. The Tracking LED will flash when the remote clamp is higher, even when the control signal is above and not limited by it.

If the Output Reverse feature is set up for a signal-to-close valve, the complement of the designated signal is used as the remote low

Note:

Because these clamps apply only when the controller is operating automatically, they do not restrict your ability to manually adjust the actuator control signal.

When setting these clamps, keep in mind that they are applied after flow characterization and valve dead band compensation but before the tight shut-off response and output reverse.

A 4 to 20 mA output is automatically generated with an offset zero, so you do not have to define that offset by setting the corresponding output clamp.

September 2005 IM301 (6.1.3)


output clamp. The remote device must then be set up to decrease its output when a higher low clamp is desired.

Tight Shut OffResponse

When the intended recycle flow rate is zero, the control valve should be fully seated and the recycle flow path completely blocked. Unfor-tunately, this ideal can not always be achieved, particularly with worn valves, or those with teflon seats. The result can be a slight leakage that wastes energy and produces an annoying sound.

Reducing the low output clamp (see page 100) to more fully seat the valve would produce a range of control signal variations that would have little effect on the actual flow rate. A better solution is to force the control signal to zero when the control response is below its low clamp and the possibility of surge is low.

This result can be obtained by setting a non-zero Tight Shut-Off Line Distance [SPEC:A d 1], thus defining a non-zero tight shut-off mar-gin (see page 74). The controller will then force the actuator control signal to zero (100 percent for a signal-to-close valve) when the intended valve position is at the low clamp and the operating point is to the right of the tight shut-off line.

Once this feature is activated, the displayed output will remain at zero until operating conditions dictate that the control valve should be opened. At this point, the control signal jumps back to its low clamp before the controller’s response to those conditions is added. For example, any Recycle Trip response would begin from the low clamp, rather than from zero.

To disable tight shut off, set its line distance to 99.9 percent.

Output Reverse The actuator control signal is adapted to the recycle or blow-off valve’s direction (signal-to-close or signal-to-open) by setting the Recycle Valve Direction [MODE:A REV] parameter:

• Direct action [REV Off] should be selected for a signal-to-open, fails-closed valve. The actuator control signal will then increase when additional flow is needed to prevent surge.

• Reverse action [REV On] should be selected for a signal-to-close, fails-open valve. The actuator control signal will then decrease when additional flow is needed to prevent surge.

Note:The remote low clamp is ignored when the controller is operating in its Stop or Purge state. It applies during manual operation only if the Manual Override parameter is disabled, in which event raising the remote clamp can increase the displayed output (and open the valve) but lowering it will have no effect.

September 2005 IM301 (6.1.3)


Output Tracking The Antisurge Controller can be set up as a signal selector for its final control element, so it can serve as a backup or alternate to another controller (for example, a DCS).

This feature is set up by connecting the other controller’s analog output to an unused Antisurge Controller analog input and setting the Output Tracking [MODE:A fE 5] parameter equal to that input’s channel number. For instance, if the output of the other device is connected to CH7, set fE 5 equal to 7.

If discrete input D4 is then asserted, the Antisurge Controller will set and keep its actuator control signal equal to the designated input’s signal variable (for example, SV7), the operating state will display as “Status TRACK”, and the Tracking LED will flash. The controller will indicate whether it will return to automatic or manual operation when the D4 input is cleared, and you can change that selection by press-ing the AUTO/MAN key or forcing the Automatic coil. In either case, the transfer will be bumpless (there will be no discontinuity or rapid change in the output):

• When returning from output tracking to Manual Operation (see page 32), the control signal remains constant.

• When the controller returns to automatic operation, it sets the effective value of its DEViation to zero, then ramps it to the actual value (calculated from the analog inputs) at a rate set by the General Ramp Rate [PID:A G].

Bumpless transfers to output tracking should be implemented in the other controller.

If the Default Output Fallback [MODE:A fD 3 1] is enabled and this feature is active, the controller will continuously calculate a filtered value of the tracking input signal that would be relatively unaffected by that signal’s failure. If that signal then failed, the controller would flash the Auto LED and ramp its output signal to its averaged value. If you then initiated manual operation, ramped the output to another value, and restored automatic operation, the control signal would remain constant at that manually set value.

This feature can be disabled by setting fE 5 to Off.

September 2005 IM301 (6.1.3)



Chapter 9 States and TransitionsThis chapter tells how to set up the Antisurge Controller’s automatic sequencing, manual operation, and redundant control features.

Operating State As described in the Automatic Sequences section in Chapter 9 of IM302, loading and unloading of a compressor is sequenced mainly by its Performance Controller. Provided neither redundant control nor output tracking is active, an Antisurge Controller will participate primarily by selecting an appropriate operating state in response to changes in its Operating State Request Signals:

• When its compressor is stopped or idling, an Antisurge Control-ler operates in a Stop state that fully opens the recycle valve. If the compressor is stopped, this minimizes any reverse flow or rotation that might occur if the discharge check valve leaked. If it is idling, this minimizes the drive power and risk of surge.

• If the compressor is then purged, the Antisurge Controller can select a Purge state that fully closes the recycle valve so purge gas can be forced through the compressor.

• When the compressor is loaded, the Antisurge Controller selects its Run state, which reduces the recycle rate as much as possible without risking surge. It will continue to modulate that valve as needed to prevent surge with a minimum of recycling as long as the compressor is running.

• While the compressor is being unloaded, the Antisurge Control-ler will either ramp its recycle valve open (a normal shutdown) or open it as fast as possible (an emergency shutdown).

The controller startup and shutdown features initiate and stop the continuous recalculation of its output signals, thus providing transi-tions between its Run and Stop operating states. While these might be used to sequence a compressor startup or shutdown, they can alternately be set up to load and idle a running compressor.

Operating StateRequest Signals

An Antisurge Controller can execute a shutdown and operate in its Stop state only if the Minimum Flow and Pressure [COND:A LVL 1] or Minimum Speed [COND:A LVL 2] has a non-zero value or the Stop Requests [MODE:A fB 1] are enabled:

• If SV1 (usually a flow) or SV2 (usually the discharge pressure) falls below the Minimum Flow and Pressure or the Rotational Speed (see page 52) falls below the Minimum Speed, the con-troller assumes the compressor is being unloaded and initiates a normal shutdown. Setting either threshold to zero disables the corresponding tests, as does the failure of their analog inputs.

September 2005 IM301 (6.1.3)

104 Chapter 9: States and Transitions

• If the Stop Requests are enabled, a normal shutdown is initiated if discrete input D6 is asserted or a designated Stop/Purge Companion [MODE:A fB –] controller selects or initiates its stop state or shutdown sequence.

• If the Stop Requests are enabled, an emergency shutdown can be initiated by asserting this controller’s D2 discrete input, but not that of any Stop/Purge Companion.

If the Purge State [MODE:A fB 2] is enabled, it is selected whenever this controller is operating in its Shutdown state and its D3 discrete input or that of its Stop/Purge Companion is asserted.

StartupConfiguration

In most applications, an Antisurge Controller participates in a startup by simply switching to its Run state, which will then slowly close the valve as needed to prevent surge with a minimum of recycling.

However, because temperature and pressure measurements will often lag the actual usually be inaccurate during major process tran-sitions, any Application Function [MODE:A fA] that calculates the Polytropic Head Exponent (see page 52) will switch to the Default Sigma [COND:A CONST 4] when the compressor is unloaded. Dur-ing any subsequent startup, the Sigma Filter Constant [PID:A Tf 2] will effect a gradual transition to the calculated value.

ShutdownConfiguration

A normal shutdown ramps the recycle valve to the position defined by the Recycle High Clamp [COND:A OUT HIGH] at the Stopping Ramp Rate [COND:A LVL 3]. If that ramp rate is set to zero (0.00), the control signal is immediately set to the high-clamp position, thus opening the valve as rapidly as possible. If the Safety On AutoReset [MODE:A fB 3] is enabled, initiating a shutdown will also reset the Surge Counters (see page 76) to zero.

Stop State While operating in the Stop state, the controller holds the recycle valve fully open, as defined by the Recycle High Clamp [COND:A OUT HIGH]. In addition, manual control cannot be initiated while the Stop state is selected unless Manual Override or Manual While Stopped is enabled (see Manual Override).

Valve SharingShutdowns

In a valve-sharing application (see page 91), some compressors may be running while others are shut down. The primary Antisurge Controller will then modulate the recycle valve as required to protect the compressors whose controllers are operating in the Run state (if its own compressor section is unloaded, it will display its operating state as “Status OFF”).

Note: Prior to revision 756-001, specifying a Stop/Purge Companion dis-abled an Antisurge Controller’s own D2, D3, and D6 discrete inputs.

September 2005 IM301 (6.1.3)


Any controller that continues to operate in the Run state after its compressor is shut down will probably calculate a very negative DEViation, which would cause the primary controller to fully open its shared valve in a needless attempt to protect a stopped compres-sor. Thus, each valve-sharing controller must be set up to select its Stop state when its compressor is not running, either by defining non-zero flow, pressure, or speed thresholds or by enabling and asserting a discrete shutdown request.

ManualOverride

To protect against surge while operating in manual, the controller will normally revert to automatic if the operating point moves to the left of the Recycle Trip control line. It will also revert to automatic if its operating state inputs dictate a transfer out of the Run state.

You can override these behaviors by enabling Manual Override [MODE:A MOR]. The controller will then remain in manual until the operator selects automatic operation, even if the compressor surges or is shut down.

When manually operating the controller via its Modbus interface, you can determine whether or not Manual Override is enabled by reading the Manual Override coil or discrete, and can enable and disable this feature by setting and clearing that coil.

If Manual Override is disabled (as recommended), the controller cannot be manually operated while the Stop state is selected unless you have enabled Manual While Stopped [MODE:A fB 4]. If fB 4 is On and the operating point is to the left of the Recycle Trip line, you can select manual only if the Stop state is selected.

Caution:Off is the “safe” Manual Override setting. We advise you not to permanently enable that parameter, because it disables all surge protection while the recycle flow is being manually controlled.

September 2005 IM301 (6.1.3)

106 Chapter 9: States and Transitions

AlternateParameter Sets

The Antisurge Controller supports up to three alternate sets of con-figuration and tuning parameters, as described in Chapter 3 of IM300/H. The Store Alternate Parameters [MODE LOCK 3 •] key sequence can be used to create them, while the Recall Alternate Parameters [MODE LOCK 3 • •] procedure replaces the working set with one of the alternates.

The Antisurge Controller also supports automatic switching between the first and second alternate sets. If Remote Parameter Switching [MODE:D LOCK 3] is enabled, clearing discrete input D7 will recall the first alternate parameter set and asserting that input will recall the second set. For example, if you had two compressors that could be operated either in series or in parallel, you could create a param-eter set for each application and use D7 to switch between them.

RedundantTracking

As described in the Redundant Controllers section in Chapter 8 of IM300/H, you can install one Antisurge Controller as an on-line “hot” backup to another.

The main controller and its backup must have Redundant Tracking [MODE:D fE 1] enabled and have the same Controller ID Number [MODE:D COMM 0]. If they are also given the same Computer ID Number [MODE:D COMM 0 •], Modbus While Tracking [MODE:D LOCK 0] must be disabled. For Antisurge Controllers, the Tracking discrete input is always D1.

A tracking Antisurge Controller lights its Tracking LED, displays its operating state as “Status TRACK”, and monitors and duplicates the outputs and auto/manual status of the active controller.

SwitchingConditions

The redundant switching device is usually triggered by one of the main controller’s Fault Relays (see page 45). That relay (usually CR1) is set up for normally-closed operation, so an automatic switch to the backup controller will occur if it de-energizes.

In addition, CR1 can be configured to indicate any one condition from Table 3-4, and either it or a hardware fault would then trigger a switchover. If you want more than one of those conditions to initiate a control transfer, they can be assigned to additional relays wired in series with CR1.

Note:Remote Parameter Switching must be enabled in both Parameter Sets 1 and 2 in order to alternate between them by asserting and clearing D7.

September 2005 IM301 (6.1.3)



Appendix A Configuration ParametersThis appendix describes each Antisurge Controller configuration parameter, including:

• its functional name and a description of that function,

• the range of values it can be given,

• the sequence of keys you must press to view or change it from the Engineering Panel (often used as an alternate name),

• its confirming display prompt,

• any restrictions on the order in which it must be entered, and

• cross-references to the sections of this manual in which the asso-ciated controller features are discussed.

Alternate Parameters The Antisurge Controller can store three alternate sets of parameter values (in addition to the set it is using) and supports Alternate Parameter Sets (see page 106) via discrete input D7.

Normalized andPercentage Values

Most numeric parameters are stored and used in a normalized for-mat, but are entered and displayed as the equivalent percentages. Although this distinction is usually academic, failing to take it into consideration can cause scaling problems.

If a parameter's defining equation calls for a normalized value but this listing indicates it is a percentage (##.#), the value you give it should be 100 times that calculated from the formula.

Keyboard Entry Pressing the indicated keys will produce the listed confirming dis-play, which consists of a prompt followed by the current value. For array parameters, that prompt will include a “#” representing the digit corresponding to the array element.

Values that are selected from a list by pressing the decimal key are shown as “Value” or “Valu”. OFF/ON or OFF/HIGH/LOW choices are shown as such and are selected by pressing the corresponding key (0, 1, HIGH, or LOW). Values that are entered by pressing one or more numeric keys are shown as a series of “#” symbols repre-senting digits, possibly including an automatically-placed decimal point. The space before a negative value is replaced by a “–”. A hexadecimal ten leading digit is entered by pressing HIGH and dis-plays as “A” (100.0 is entered as HIGH 0 0 and displays as A0.0).

Note: Detailed information on Engineering Panel configuration and alter-nate parameter procedures can be found in Chapter 3 of IM300/H.

September 2005 IM301 (6.1.3)

108 Appendix A: Configuration Parameters

COND:A β 3 In a load-sharing application, this parameter defines the proximity to the surge control line (S) above which this antisurge controller can increase its recycle rate when the station controller determines less header flow is needed (see Figure 7-4).

Range: 0.00 to 1.99

Display: ∫3 #.##

Reference: Primary Capacity Control . . . . . . . . . . . . . . . . 92

COND:A β 5 This parameter defines the scaling coefficient for the squared mass flow rate (W2) used to compute proximity to surge.

Range: 00.0 to 99.9

Display: ∫5 ##.#

Reference: Reported Flow . . . . . . . . . . . . . . . . . . . . . . . . 86

COND:A CONST 1 If the Default Output Fallback [MODE:A fD 3 1] is enabled, this parameter defines the minimum value at which it will initially hold the control signal (it selects the higher of this parameter or a filtered his-torical control signal).

Range: 00.0 to 99.9 percent

Display: CO1 ##.#

Enter After: MODE:A REV

Reference: Default Output Fallback . . . . . . . . . . . . . . . . . 67

COND:A CONST 2 This parameter defines the set point for the Minimum Flow Fallback [MODE:A fD 3 2].


Display: CO2 ##.#

Reference: Minimum Flow Fallback . . . . . . . . . . . . . . . . . 68

COND:A CONST 3 If the Compression Ratio Fallback [MODE:A fD 3 3] is enabled, this parameter defines the compression ratio used to calculate proximity to surge when the discharge pressure input fails.

Range: 0.00 to 9.99

Display: CO3 #.##

Reference: Compression Ratio Fallback . . . . . . . . . . . . . 69

Recycling Threshold

Mass Flow Coefficient

Fallback MinimumRecycle

Default Minimum Flow

Default CompressionRatio

September 2005 IM301 (6.1.3)


COND:A CONST 4 If the selected Application Function [MODE:A fA] calculates a poly-tropic head exponent, this parameter defines the exponent value that is used during startups. If the Sigma Fallback [MODE:A fD 3 4] is enabled, this value is also used if the discharge pressure, suction temperature, or discharge temperature input fails.

Range: .000 to .999

Display: CO4 .###

Reference: Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Discharge Flow Measurement . . . . . . . . . . . . 57Sigma Fallback . . . . . . . . . . . . . . . . . . . . . . . . 69Polytropic Head Fallback . . . . . . . . . . . . . . . . 70Startup Configuration . . . . . . . . . . . . . . . . . . 104

COND:A CONST 5 If the Speed Fallback [MODE:A fD 3 5] is enabled, this parameter defines the rotational speed used when the speed input signal fails.


Display: CO5 ##.#

Reference: Speed Fallback. . . . . . . . . . . . . . . . . . . . . . . . 69

COND:A CONST 6 If the Function 5 Fallback [MODE:A fD 3 6] is enabled, this parame-ter defines the default value used for that characterizer’s argument if the selected f5 Argument [MODE:A SS 9] input fails.


Display: CO6 ##.#

Reference: Function 5 Fallback . . . . . . . . . . . . . . . . . . . . 70

COND:A CONST 7 If the Default Output Fallback [MODE:A fD 3 1] is disabled and the Adjacent Section Flow Fallback [MODE:A fD 3 7] is enabled, this parameter defines the default value used for the adjacent section flow rate if communication with that section’s Antisurge Controller fails or that controller’s flow input fails.


Display: CO7 ##.#

Reference: Adjacent Section Flow Fallback . . . . . . . . . . . 70

COND:A CONST 8 If the Valve Sharing Fallback [MODE:A fD 3 8] is enabled, this parameter defines the surge limit line slope coefficient that a primary Antisurge Controller would use if communication with any valve-sharing companion fails.

Range: .000 to .999

Display: CO8 .###

Reference: Valve-Sharing Fallback. . . . . . . . . . . . . . . . . . 70

Default Sigma

Default Speed

Default f5 Argument

Default AdjacentSection Flow

Alternate K

September 2005 IM301 (6.1.3)


COND:A f(X) 1 #and X 1 #

These parameters characterize the surge limit in the primary coordi-nate system (that is, the minimum value of X as a function of Y).

Range: 0.00 to 9.99 [X]0.00 to 9.99 [f(X)]

Display: X1# #.## [X]Y1# #.## [f(X)]

Reference: Characterizing Functions . . . . . . . . . . . . . . . . 64


These parameters characterize the reported flow measurement in multisection compressor applications.

Range: 0.00 to 9.99 [X]0.00 to 9.99 [f(X)]

Display: X2# #.## [X]Y2# #.## [f(X)]

Reference: Displayed Net Flow . . . . . . . . . . . . . . . . . . . . 62Characterizing Functions . . . . . . . . . . . . . . . . 64Minimum Flow Fallback . . . . . . . . . . . . . . . . . 68Reported Flow . . . . . . . . . . . . . . . . . . . . . . . . 86Upstream Section Flow Known . . . . . . . . . . . 87Downstream Section Flow Known . . . . . . . . . 89Load Balancing . . . . . . . . . . . . . . . . . . . . . . . 93


These parameters usually characterize the X primary coordinate as a function of the rotational speed.

Range: .000 to .999 [X]0.00 to 9.99 [f(X)]

Display: X3# .### [X]Y3# #.## [f(X)]

Reference: Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Characterizing Functions . . . . . . . . . . . . . . . . 64Speed Fallback . . . . . . . . . . . . . . . . . . . . . . . 69


These parameters characterize the shape of the regions between the various control lines.

Range: .000 to .999 [X]0.00 to 9.99 [f(X)]

Display: X4# .### [X]Y4# #.## [f(X)]

Reference: Characterizing Functions . . . . . . . . . . . . . . . . 64Control Lines . . . . . . . . . . . . . . . . . . . . . . . . . 71Cold-Recycle Control . . . . . . . . . . . . . . . . . . . 95

Y CoordinateCharacterizer

Reported FlowCharacterizer

X CoordinateCharacterizer

Control LineCharacterizer

September 2005 IM301 (6.1.3)



These parameters characterize the surge limit as a function of the secondary coordinate variable (V) specified by the f5 Argument [MODE:A SS 9].

Range: .000 to .999 [X]0.00 to 9.99 [f(X)]

Display: X5# .### [X]Y5# #.## [f(X)]

Reference: Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Characterizing Functions . . . . . . . . . . . . . . . . 64Function 5 Fallback . . . . . . . . . . . . . . . . . . . . 70


These parameters characterize the series load-balancing variable (L) as a function of the Load Balancing Variable [MODE:A fD 9].

Range: .000 to .999 [X]0.00 to 9.99 [f(X)]

Display: X6# .### [X]Y6# #.## [f(X)]

Reference: Characterizing Functions . . . . . . . . . . . . . . . . 64Load Balancing. . . . . . . . . . . . . . . . . . . . . . . . 93

COND:A LVL 1 This parameter defines the minimum values of SV1 and SV2 below which the compressor is assumed to be shut down and the recycle valve is held fully open.


Display: LV1 ##.#

Reference: Operating State Request Signals . . . . . . . . . 103

COND:A LVL 2 This parameter defines the minimum rotational speed below which the compressor is assumed to be shut down and the recycle valve is held fully open.


Display: LV2 ##.#


COND:A LVL 3 This parameter defines the rate at which the recycle valve is opened during a normal shutdown. Setting it to zero causes the output to jump to the Recycle High Clamp [COND:A OUT HIGH].

Range: 0.00 to 9.99 repeats per minute

Display: LV3 #.##

Reference: Shutdown Configuration . . . . . . . . . . . . . . . . 104

General Characterizer

Balancing VariableCharacterizer

Minimum Flow andPressure

Minimum Speed

Stopping Ramp Rate

September 2005 IM301 (6.1.3)


COND:A M 0 In a load-sharing application, this parameter sets the gain applied to station control signal when calculating the primary capacity control component of the antisurge control response.

Range: -9.99 to 9.99

Display: M0 #.##


COND:A M # If the corresponding Decoupling Controller [MODE:A SS 0 #] is enabled, each of these parameters sets the gain applied to its con-trol response.

Range: -9.99 to 9.99

Display: M# #.##

Reference: Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . 83

COND:A OUTHIGH

This parameter defines the upper limit of the displayed actuator con-trol signal.

Range: Recycle Low Clamp to 99.9 percent

Display: OUH ##.#


Reference: Output Clamps . . . . . . . . . . . . . . . . . . . . . . . 100Shutdown Configuration. . . . . . . . . . . . . . . . 104

COND:A OUT LOW This parameter defines the lower limit of the displayed actuator con-trol signal.

Range: 00.0 percent to Recycle High Clamp

Display: OUL ##.#


Reference: Output Clamps . . . . . . . . . . . . . . . . . . . . . . . 100Remote Low Output Clamp . . . . . . . . . . . . . 100

COND:A OUT 1 This parameter sets the bias used to compensate for a control valve dead band. If desired, this bias should be set to one-half the valve’s dead band (in percent of span), otherwise this parameter should be set to zero.


Display: OU1 ##.#

Reference: Valve Dead Band Compensation. . . . . . . . . . 99Manual Operation . . . . . . . . . . . . . . . . . . . . . 32

Recycling Gain

Decoupling Gain

Recycle High Clamp

Recycle Low Clamp

Valve Dead-Band Bias

September 2005 IM301 (6.1.3)


COND:A SP 2 If Discharge Pressure Limiting [MODE:A MVAR 2] is enabled, this parameter sets its high-limiting control threshold.


Display: SP2 ##.#

Reference: Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . 82

COND:A SP 3 If Suction Pressure Limiting [MODE:A MVAR 3] is enabled, this parameter sets its low-limiting control threshold.


Display: SP3 ##.#


COND:D β 0 This parameter is the scaling coefficient for the second analog out-put when the Displayed or Net Mass Flow (Flow or UsrQ) is selected as the Second Output Assigned Variable [COND:D OUT 2].

Range: 00.0 to 99.9

Display: ∫0 ##.#

Reference: Displayed Flow . . . . . . . . . . . . . . . . . . . . . . . . 61Displayed Net Flow. . . . . . . . . . . . . . . . . . . . . 62

COND:D BIAS # These parameters set the biases used to convert signal variables into the process variables used by the control algorithms.


Display: BI# ##.#

Reference: Process Variables. . . . . . . . . . . . . . . . . . . . . . 40

COND:D CONST 0 This parameter defines the minimum number of surges that must be detected to trigger a Surg discrete output.

Range: 00 to 99 surges

Display: CO0 ##

Reference: Surge Counters . . . . . . . . . . . . . . . . . . . . . . . 76

COND:D CONST 1 This parameter defines the maximum duration of a surge event time period during which the surge event count must reach the Surge Event Threshold to trigger a Surg discrete output.

Range: 000 to 999 seconds

Display: CO1 ###

Reference: Surge Counters . . . . . . . . . . . . . . . . . . . . . . . 76

Maximum DischargePressure

Minimum SuctionPressure

OUT2 Mass FlowCoefficient

Process Variable Bias

Surge Event Threshold

Surge Event Duration

September 2005 IM301 (6.1.3)


COND:D CONST 2 Mass flow rate computations add this offset to the Compensating Pressure Input [MODE:D fD 2] measured variable to obtain the absolute compensating pressure.

Range: 00.0 to 99.9

Display: CO2 ##.#

Reference: Compensating Pressure . . . . . . . . . . . . . . . . 59

COND:D CONST 3 Mass flow rate computations add this offset to the Compensating Temperature Input [MODE:D fD 3] measured variable to obtain the absolute compensating temperature.

Range: 000 to 999

Display: CO3 ###

Reference: Compensating Temperature . . . . . . . . . . . . . 59

COND:D CONST 5 Position failure (PosF) relays are tripped when the position input (CH7) deviates from the control signal by more than the Position Failure Threshold [COND:D LVL 5] for at least the number of sec-onds specified by this parameter.

Range: 0.00 to 9.99 seconds

Display: CO5 #.##

Reference: Valve Position Test . . . . . . . . . . . . . . . . . . . . 43

COND:D DISPLAY0 #

Each of these parameters determines whether or not the corre-sponding measured variable can be viewed in the Auxiliary readout.

Range: Off variable cannot be displayedOn variable can be displayed

Display: D0# OFF/ON

Reference: Measured Variables . . . . . . . . . . . . . . . . . . . . 40

COND:D DISPLAY0 # –

Each of these parameters defines the label shown when the corre-sponding measured variable is displayed in the Auxiliary readout.

Range: any eight symbols from Table 3-1

Display: AAAAAAAA (selected symbol flashes)


COND:D DISPLAY0 # HIGH

Each of these parameters defines the value the Auxiliary readout would display for the corresponding measured variable if the value of its signal variable was 100.0 percent.

Range: –9999 to 9999

Display: 0#H ####


CompensatingPressure Offset

CompensatingTemperature Offset

Position Failure Delay

Measured VariableDisplay

Measured VariableLabel

Measured VariableMaximum

September 2005 IM301 (6.1.3)


COND:D DISPLAY0 # LOW

Each of these parameters defines the value the Auxiliary readout would display for the corresponding measured variable if the value of its signal variable was zero.

Range: –9999 to 9999

Display: 0#L ####


COND:D DISPLAY0 # •

Each of these parameters defines the position of the decimal point in the corresponding measured variable display.

Range: 0 #### (no decimal)1 ###. (trailing decimal)2 ##.#3 #.##4 .### (leading decimal)

Display: 0#. 4321 (selected digit is replaced by •)


COND:D DISPLAY1 1

This parameter determines whether the calculated polytropic head (Hpr) and its exponent (σ) can be displayed by the AUX readout.


Display: D11 OFF/ON

Reference: Calculated Variable Displays . . . . . . . . . . . . . 60

COND:D DISPLAY1 2

This parameter determines whether or not the compression ratio (Rc) calculated variable can be displayed by the AUX readout.


Display: D12 OFF/ON


COND:D DISPLAY1 3

This parameter determines whether or not the temperature ratio (Rt) calculated variable can be displayed by the AUX readout.


Display: D13 OFF/ON


Measured VariableMinimum

Measured VariableDecimal

Polytropic ExponentDisplay

Compression RatioDisplay

Temperature RatioDisplay

September 2005 IM301 (6.1.3)


COND:D DISPLAY1 4

This parameter determines whether or not the rotational speed (Speed) calculated variable can be displayed by the AUX readout.


Display: D14 OFF/ON

Reference: Calculated Variable Displays . . . . . . . . . . . . . 60Displayed Speed . . . . . . . . . . . . . . . . . . . . . . 61

COND:D DISPLAY1 4 HIGH

This parameter is used to scale the Speed readout.

Range: 00000 to 99999

Display: 14H#####

Reference: Displayed Speed . . . . . . . . . . . . . . . . . . . . . . 61

COND:D DISPLAY1 5

This parameter determines whether or not the displayed mass flow (Flow) calculated variable can be displayed by the AUX readout.


Display: D15 OFF/ON

Reference: Calculated Variable Displays . . . . . . . . . . . . . 60Displayed Flow. . . . . . . . . . . . . . . . . . . . . . . . 61


This parameter is used to scale the Flow readout.

Range: 00000 to 99999

Display: 15H#####

Reference: Displayed Flow. . . . . . . . . . . . . . . . . . . . . . . . 61

COND:D DISPLAY1 5 •

This parameter defines the position of the decimal point in the AUX readout’s Flow and UsrQ calculated variable displays.

Range: 0 #### (no decimal)1 ###. (trailing decimal)2 ##.#3 #.##4 .### (leading decimal)

Display: 15. 4321 (selected digit is replaced by •)

Reference: Calculated Variable Displays . . . . . . . . . . . . . 60Displayed Flow. . . . . . . . . . . . . . . . . . . . . . . . 61Displayed Net Flow . . . . . . . . . . . . . . . . . . . . 62

Rotational SpeedDisplay

Rotational SpeedCoefficient

Mass Flow Display

Displayed FlowCoefficient

Flow Variables Decimal

September 2005 IM301 (6.1.3)


COND:D DISPLAY1 7

This parameter determines whether or not the UsrQ (net mass flow) calculated variable can be displayed by the AUX readout.


Display: D17 OFF/ON

Reference: Calculated Variable Displays . . . . . . . . . . . . . 60Displayed Net Flow. . . . . . . . . . . . . . . . . . . . . 62


This parameter is used to scale the UsrQ readout.

Range: 00000 to 99999

Display: 17H#####

Reference: Displayed Net Flow. . . . . . . . . . . . . . . . . . . . . 62

COND:D f(X) 2 #and X 2 #

These parameters characterize the recycle flow rate as a function of the control response.

Range: .000 to .999 [X]0.00 to 9.99 [f(X)]

Display: X2# .### [X]Y2# #.## [f(X)]

Reference: Displayed Net Flow. . . . . . . . . . . . . . . . . . . . . 62Load Balancing. . . . . . . . . . . . . . . . . . . . . . . . 93

COND:D GAIN # These parameters set the gains used to convert signal variables into the process variables used by the control algorithms.

Range: .000 to 1.000

Display: GA# .###

Reference: Process Variables. . . . . . . . . . . . . . . . . . . . . . 40

COND:D LVL 5 This parameter sets the minimum deviation of the valve position input (SV7) from the control signal that will trigger any Position Fail-ure (PosF) relays.


Display: LV5 ##.#

Reference: Valve Position Test. . . . . . . . . . . . . . . . . . . . . 43

Net Flow Display

Net Flow Coefficient

Recycle FlowCharacterizer

Process Variable Gain

Position FailureThreshold

September 2005 IM301 (6.1.3)


COND:D OUT 2 This parameter identifies the internal variable from which the value of the OUT2 analog output signal is calculated.

Range: Out actuator control signalFlow displayed mass flow

S proximity to surgeUsrQ net mass flow

Display: OU2 Valu

Reference: Analog Outputs . . . . . . . . . . . . . . . . . . . . . . . 42

MODE:A ANIN 4 This parameter selects either analog input CH4 or a companion Speed, Fuel, or Performance Controller (identified by Controller ID Number) as the source of the rotational speed signal.

Range: Off CH4 used by default1 to 8 get speed from companion #

Display: AN4 OFF/#

Reference: Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

MODE:A fA This parameter selects the specific method used to calculate the Ss proximity-to-surge variable.

Range: see Appendix F

Display: fA ##

Reference: Application Function. . . . . . . . . . . . . . . . . . . . 63

MODE:A fB 1 This parameter enables the discrete and serial stop requests. If it is disabled, there is no way to initiate an ESD and a normal, ramped shutdown would be initiated only if the pressure or flow fell below the Minimum Flow and Pressure [COND:A LVL 1] or the rotational speed dropped below the Minimum Speed [COND:A LVL 2].

Range: Off use analog inputs onlyOn also use discrete and serial requests

Display: fB1 OFF/ON

Reference: Operating State Request Signals. . . . . . . . . 103

MODE:A fB 2 This parameter enables or disables the purge state, in which the recycle valve is held fully closed so purge gas can be forced through the compressor.

Range: Off Purge state disabledOn Purge state enabled

Display: fB2 OFF/ON

Reference: Operating State Request Signals. . . . . . . . . 103

Second OutputAssigned Variable

Rotational SpeedSource


Stop Requests

Purge State

September 2005 IM301 (6.1.3)


MODE:A fB 3 If this parameter is enabled, the Safety On surge count is automati-cally reset to zero when the compressor is shut down and held there until it is restarted.

Range: Off surge count is not zeroed by shutdownOn surge count is zeroed by shutdown

Display: fB3 OFF/ON

Reference: Surge Counters . . . . . . . . . . . . . . . . . . . . . . . 76Shutdown Configuration . . . . . . . . . . . . . . . . 104

MODE:A fB 4 If Manual Override [MODE:A MOR] is disabled, this parameter determines whether or not the controller can be manually operated while the compressor is shut down.

Range: Off manual cannot be selected in stopOn manual can be selected in stop

Display: fB4 OFF/ON

Reference: Manual Override . . . . . . . . . . . . . . . . . . . . . . 105

MODE:A fB – If the Stop Requests [MODE:A fB 1] are enabled, this parameter identifies the companion controller (by Controller ID Number) from which stop and purge requests are obtained.

Range: Off use local inputs only1 to 8 get status from companion #

Display: fB- OFF/#


MODE:A fC 1 This parameter selects the analog input used as the argument for the Control Line Characterizer [COND:A f(X) 4 # and X 4 #]:

Range: Off calculated flow measurement (∆Po,c)1 to 8 signal variable SV#

Display: fC1 OFF/#

Reference: Control Lines . . . . . . . . . . . . . . . . . . . . . . . . . 71Cold-Recycle Control . . . . . . . . . . . . . . . . . . . 95

MODE:A fC 2 This parameter determines whether or not Application Function [MODE:A fA] 65 through 69 use any temperature inputs to calculate proximity to surge.

Range: Off temperature inputs usedOn temperature inputs not used

Display: fC2 OFF/ON

Reference: Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Discharge Flow Measurement . . . . . . . . . . . . 57Aftercooler Flow Measurement. . . . . . . . . . . . 57

Safety On AutoReset

Manual While Stopped

Stop/Purge Companion

Control Line Argument

Constant Sigma

September 2005 IM301 (6.1.3)


MODE:A fC 3 This parameter determines whether the margin of safety varies with the rate of the operating point’s approach to its surge limit.

Range: Off margin does not vary with dS/dtOn margin does vary with dS/dt

Display: fC3 OFF/ON

Reference: Derivative Response . . . . . . . . . . . . . . . . . . . 74

MODE:A fC 4 This parameter determines whether the Recycle Trip step size var-ies with the rate of the operating point’s approach to its surge limit.

Range: Off step size does not vary with dS/dtOn step size does vary with dS/dt

Display: fC4 OFF/ON

Reference: Recycle Trip Response . . . . . . . . . . . . . . . . . 80

MODE:A fC 8 This parameter selects the valve characterizer used to calculate the control signal (intended valve position) from the control response (intended flow rate).

Range: Off linear flow valveHigh quick-opening valveLow equal-percentage valve

Display: fC8 OFF/HIGH/LOW

Reference: Valve Flow Characterization . . . . . . . . . . . . . 98

MODE:A fC 9 In a load-sharing application, this parameter selects the load-balancing method. If series load balancing is enabled, the controller will report its series load balancing parameter (L) to its companion controllers. If it is disabled, the controller will report a flow measure-ment (∆Po,r) or squared mass flow rate (W2).

Range: Off parallel load sharingOn series load sharing

Display: fC9 OFF/ON

Reference: Reported Flow . . . . . . . . . . . . . . . . . . . . . . . . 86Load Balancing . . . . . . . . . . . . . . . . . . . . . . . 93

Derivative Response

Derivative Recycle Trip

Valve FlowCharacterizer

Series Load Variable

September 2005 IM301 (6.1.3)


MODE:A fD 2 This parameter defines the process variables that must exhibit rapid changes to be interpreted as a surge. Regardless of which method is selected, a surge is always assumed if the operating point moves to the left of the Safety On control line.

Range: Off Safety On Line only1 both flow (SV1) and pressure (SV2)2 either flow (SV1) or pressure (SV2)3 flow (SV1) only4 pressure (SV2) only

Display: fD2 OFF/#

Reference: Surge Detection . . . . . . . . . . . . . . . . . . . . . . . 75

MODE:A fD 3 1 Enabling this parameter configures the controller to hold the control response constant (unless manually changed) if it is unable to calcu-late the proximity to surge. The initial value of the control signal will depend on the Fallback Minimum Recycle [COND:A CONST 1].

Range: Off antisurge loop continues to operateOn automatic output changes suspended

Display: fD31 OFF/ON

Reference: Default Output Fallback . . . . . . . . . . . . . . . . . 67Output Tracking . . . . . . . . . . . . . . . . . . . . . . 102

MODE:A fD 3 2 Enabling this parameter configures the controller to calculate Ss as the ratio of the Default Minimum Flow [COND:A CONST 2] and the calculated flow measurement (∆Po,c) when it is unable to calculate the numerator defined by the chosen fA mode.

Range: Off Default Output Fallback is usedOn Default Minimum Flow is used


Reference: Minimum Flow Fallback . . . . . . . . . . . . . . . . . 68

MODE:A fD 3 3 Enabling this parameter configures the controller to calculate Ss using the Default Compression Ratio [COND:A CONST 3] when the discharge pressure input fails.

Range: Off Default Output Fallback is usedOn Default Compression Ratio is used


Reference: Compression Ratio Fallback. . . . . . . . . . . . . . 69

Surge DetectionMethod

Default Output Fallback

Minimum Flow Fallback

Compression RatioFallback

September 2005 IM301 (6.1.3)


MODE:A fD 3 4 Enabling this parameter configures the controller to calculate Ss using the Default Sigma [COND:A CONST 4] when either tempera-ture or the discharge pressure input fails.

Range: Off Default Output Fallback is usedOn Default Sigma is used


Reference: Sigma Fallback . . . . . . . . . . . . . . . . . . . . . . . 69

MODE:A fD 3 5 Enabling this parameter configures the controller to calculate Ss using the Default Speed [COND:A CONST 5] when the specified Rotational Speed Source [MODE:A ANIN 4] fails.

Range: Off Minimum Flow Fallback is usedOn Default Speed is used


Reference: Speed Fallback . . . . . . . . . . . . . . . . . . . . . . . 69

MODE:A fD 3 6 Enabling this parameter configures the controller to calculate Ss using the Default f5 Argument [COND:A CONST 6] when it is unable to measure or calculate the specified f5 Argument [MODE:A SS 9].

Range: Off Minimum Flow Fallback is usedOn Default f5 Argument is used


Reference: Function 5 Fallback . . . . . . . . . . . . . . . . . . . . 70

MODE:A fD 3 7 Enabling this parameter configures the controller to calculate its flow rates using the Default Adjacent Section Flow [COND:A CONST 7] when communication with the designated Adjacent Section Control-ler [MODE:A SS 5] or that controller’s flow input fails. However, it will calculate the control response from the resulting flow and prox-imity to surge only if this fallback is enabled and the Default Output Fallback [MODE:A fD 3 1] is disabled.

Range: Off Default Output Fallback is usedOn Default Adjacent Section Flow is used


Reference: Adjacent Section Flow Fallback . . . . . . . . . . . 70

Sigma Fallback

Speed Fallback

Function 5 Fallback

Adjacent Section FlowFallback

September 2005 IM301 (6.1.3)


MODE:A fD 3 8 Enabling this parameter configures a valve-sharing controller to calculate Ss using the Alternate K [COND:A CONST 8] if communi-cation with any valve-sharing companion fails.

Range: Off Default Output Fallback is usedOn Alternate K is used


Reference: Valve-Sharing Fallback. . . . . . . . . . . . . . . . . . 70

MODE:A fD 3 9 Enabling this parameter configures the controller to calculate reduced head from the suction and discharge temperature and the Default Sigma [COND:A CONST 4] when either pressure input fails.

Range: Off Compression Ratio Fallback is usedOn temperature calculation is used


Reference: Polytropic Head Fallback . . . . . . . . . . . . . . . . 70

MODE:A fD 9 If Series Load Variable [MODE:A fC 9] is enabled, this parameter selects the variable that is balanced when operating far from the surge control line.

Range: Off selects the compression ratio (Rc)1 to 8 selects analog input PV#, except

4 selects the rotational speed (N) from specified Rotational Speed Source

Display: fD9 OFF/#

Reference: Load Balancing. . . . . . . . . . . . . . . . . . . . . . . . 93

MODE:A fE 4 This parameter selects the analog input, if any, that an Antisurge Controller will use as a remote low clamp for its control signal.

Range: Off disables this feature1 to 8 uses analog input SV#

Display: fE4 OFF/#

Reference: Remote Low Output Clamp . . . . . . . . . . . . . 100

MODE:A fE 5 This parameter determines which analog input, if any, the control signal will track when discrete input D4 is asserted.

Range: Off disables this feature1 to 8 tracks analog input SV#

Display: fE5 OFF/#

Reference: Output Tracking . . . . . . . . . . . . . . . . . . . . . . 102

Valve Sharing Fallback


Load BalancingVariable


Output Tracking

September 2005 IM301 (6.1.3)


MODE:A MOR This parameter determines whether manual control is suspended if the operating point moves to the left of the Recycle Trip control line.

Range: Off protection when in manualOn no protection in manual

Display: MOR OFF/ON

Reference: Manual Override . . . . . . . . . . . . . . . . . . . . . 105

MODE:A MVAR 2 If this parameter is enabled (On), the controller will increase the recycle rate to reduce the discharge pressure when it exceeds the Maximum Discharge Pressure [COND:A SP 2].

Range: Off disables Pd limitingOn enables limiting of maximum Pd

Display: MV2 OFF/ON


MODE:A MVAR 3 If this parameter is enabled (On), the controller will increase the recycle rate to raise the suction pressure when it is below the Mini-mum Suction Pressure [COND:A SP 3].

Range: Off disables Ps limitingOn enables limiting of maximum Ps

Display: MV3 OFF/ON


MODE:A REV This parameter adapts the control signal to the recycle control valve’s direction of action.

Range: Off signal-to-open recycle valveOn signal-to-close recycle valve

Display: REV OFF/ON

Enter After: COND:A CONST 1, COND:A OUT HIGH, and COND:A OUT LOW

Reference: Antisurge Control Response . . . . . . . . . . . . . 77Output Reverse . . . . . . . . . . . . . . . . . . . . . . 101

Manual Override

Caution:No automatic surge protection is provided when MOR is ON and the controller is in manual. Accidental equipment damage could then result from inappropriate manual adjustments of the output signal.

Discharge PressureLimiting

Note: Prior to software revision 752-001, PV2 limiting was not available in controllers using Application Function 01 or 02.

Suction PressureLimiting

Note: Prior to software revision 756-002, PV3 limiting was not available in controllers using Application Function 01 or 02.

Recycle ValveDirection

September 2005 IM301 (6.1.3)


MODE:A SS 0 # Each of these parameters enables or disables loop decoupling from the corresponding controller (identified by its Controller ID Number [MODE:D COMM 0]). If enabled, you must also set the correspond-ing Decoupling Gain [COND:A M #]. Entering MODE:A SS 0 0 sets all of these parameters to Off.

Range: Off decoupling from controller # disabledOn decoupling from controller # enabled

Display: SS0# OFF/ON

Reference: Loop Decoupling. . . . . . . . . . . . . . . . . . . . . . . 83

MODE:A SS 1 # Enabling one of these parameters configures an Antisurge Control-ler to include the control response of the corresponding companion controller (identified by Controller ID Number [MODE:D COMM 0]) in its PI and RT signal selection algorithm. Entering MODE:A SS 1 0 sets all of these parameters to Off.

Range: Off response of controller # is not usedOn response of controller # is used


Reference: Auxiliary Limiting. . . . . . . . . . . . . . . . . . . . . . . 83Port 1 Balancing . . . . . . . . . . . . . . . . . . . . . . . 94Cold-Recycle Control . . . . . . . . . . . . . . . . . . . 95

MODE:A SS 2 This parameter configures the Antisurge Controller to send its con-trol response to the corresponding Antisurge Controller (identified by Controller ID Number) for inclusion in its PI signal selection. This controller’s OUT readout will then be blank.

In a valve-sharing application, disable this parameter in the master controller and set it equal to the master’s Controller ID Number in all of its companion controllers.

Range: Off disables secondary valve-sharing1 to 8 output sent to companion #

Display: SS2 OFF/#

Reference: Loop Decoupling. . . . . . . . . . . . . . . . . . . . . . . 83

Decoupling Controller

Note: You cannot enable the SS 0 parameter corresponding to this con-troller’s own ID.

Valve SharingCompanion


Valve-Sharing MasterID

Note: You cannot select this controller’s own ID. Enabling this feature sets all Decoupling Controller [MODE:A SS 0 #] to Off.

September 2005 IM301 (6.1.3)


MODE:A SS 3 This parameter determines whether or not the Antisurge Controller will include the Performance Controller’s performance override response (received via Port 2) in its PI signal selection pool.

Range: Off disables performance overrideOn enables performance override

Display: SS3 OFF/ON

Reference: Performance Override . . . . . . . . . . . . . . . . . . 83

MODE:A SS 4 In load-sharing applications, this parameter selects the controller (identified by Controller ID Number) from which the primary capacity control response will obtain its S variable (proximity to the surge control line). It should select either this controller or the Performance Controller for the compressor it is protecting.

Range: Off disables primary capacity control1 to 8 S for primary capacity control selected

by companion #

Display: SS4 OFF/#


MODE:A SS 5 If the Application Function [MODE:A fA] uses an adjacent section flow, this parameter identifies the Antisurge Controller (by its Con-troller ID Number [MODE:D COMM 0]) for that compressor section.

Range: Off no adjacent section flow1 to 8 adjacent flow from companion #

Display: SS5 OFF/#

Reference: Default Output Fallback . . . . . . . . . . . . . . . . . 67Upstream Section Flow Known . . . . . . . . . . . 87Downstream Section Flow Known . . . . . . . . . 89

MODE:A SS 6 1 This parameter determines how the suction and discharge pres-sures are calculated from the process variables for analog inputs CH2 and CH3.

Range: Off PV2 = Pd, PV3 = PsHigh PV2 = ∆Pc, PV3 = Ps, Pd = PV2 + PV3Low PV2 = Pd, PV3 = ∆Pc, Ps = PV2 – PV3

Display: SS61 OFF/HIGH/LOW

Reference: Pressures. . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . 82

Performance OverrideControl

Load-SharingController

Adjacent SectionController

Note: You cannot select this controller’s own ID.

∆Pc Substitution

September 2005 IM301 (6.1.3)


MODE:A SS 6 2 This parameter determines how the suction and discharge tempera-tures are calculated from the process variables for analog inputs CH5 and CH6:

Range: Off PV5 = Td, PV6 = TsHigh PV5 = ∆Tc, PV6 = Ts, Td = PV5 + PV6Low PV5 = Td, PV6 = ∆Pc, Ts = PV5 – PV6

Display: SS62 OFF/HIGH/LOW

Reference: Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . 51

MODE:A SS 7 # If Port 2 Recycle Balancing [MODE:A SS HIGH] is Off, enabling any of these eight parameters (and the corresponding Valve Sharing Companion [MODE:A SS 1 #]) configures the Antisurge Controller to balance its recycle rate with that of a Port 1 companion controller assigned the specified Controller ID Number (#).

Range: Off controller # is not monitoredOn controller # is monitored


Reference: Port 1 Balancing . . . . . . . . . . . . . . . . . . . . . . . 94

MODE:A SS 8 This parameter selects the pressure input used to compensate the flow measurement (∆Po) for pressure drops between the flow mea-suring element and compressor inlet.

Range: Off disables this feature1 to 8 analog input PV# is used

Display: SS8 OFF/#

Reference: Control Valve Compensation . . . . . . . . . . . . . 56

MODE:A SS 9 This parameter specifies the analog input used as the argument for the General Characterizer [COND:A f(X) 5 # and X 5 #].

Range: Off f5 is a function of the polytropic headexponent (σ)

1 to 8 f5 is a function of analog input PV#

Display: SS9 OFF/#

Reference: Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Characterizing Functions . . . . . . . . . . . . . . . . 64Function 5 Fallback . . . . . . . . . . . . . . . . . . . . 70

∆Tc Substitution

Recycle BalancingController


Flow Element PressureInput

f5 Argument

September 2005 IM301 (6.1.3)


MODE:A SS – This parameter selects the analog input for the ∆Po transmitter used for low flow measurements.

Range: Off or 1 flow measurement is always PV12 to 8 PV# is low flow measurement

Display: SS- OFF/#

Reference: Dual Flow Transmitters . . . . . . . . . . . . . . . . . 55

MODE:A SS HIGH Enabling this parameter configures a load-sharing Antisurge Con-troller to balance its recycle flow rate with a target value received from the Station Controller via Port 2 serial communication. Recycle balancing is disabled by setting this and every Recycle Balancing Controller [MODE:A SS 7 #] parameter to Off.

Range: Off Port 1 Balancing used if enabledOn Port 2 Balancing is used

Display: SSH OFF/ON

Reference: Port 2 Balancing. . . . . . . . . . . . . . . . . . . . . . . 94

MODE:D ANIN # Each of these parameters identifies the zero level of the corre-sponding analog input signal (relative to its hardware configuration).

Range: Off actual zero (for example, 0 to 5 Vdc)On 20 percent offset zero (e.g., 4 to 20 mA)

Display: A# OFF/ON

Reference: Signal Variables . . . . . . . . . . . . . . . . . . . . . . . 39

MODE:D ANIN #HIGH

Each of these parameters defines the maximum value for the corre-sponding analog input’s analog-to-digital variable, above which that input is considered to have failed.


Display: A#H ##.#

Reference: Transmitter Testing . . . . . . . . . . . . . . . . . . . . 39

MODE:D ANIN #LOW

Each of these parameters defines the minimum value for the corre-sponding analog input’s analog-to-digital variable, below which that input is considered to have failed.


Display: A#L ##.#

Reference: Transmitter Testing . . . . . . . . . . . . . . . . . . . . 39

Low Flow Input

Port 2 RecycleBalancing

Offset Zero Input

Analog Input HighAlarm Limit

Analog Input LowAlarm Limit

September 2005 IM301 (6.1.3)


MODE:D COMM 0 This parameter identifies the controller in the network connected to its serial Port 1. With the exception of redundant controllers, this ID must be unique within that network.

Range: 1 to 8

Display: Ctrl# #

Reference: Redundant Tracking . . . . . . . . . . . . . . . . . . . 106ID Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . 49

MODE:D COMM 0 • This parameter identifies the controller in the networks connected to its serial Ports 2, 3, and 4. With the possible exception of redundant controllers, this ID must be unique within each of those networks.

Range: 01 to 64

Display: Comp# ##

Reference: Redundant Tracking . . . . . . . . . . . . . . . . . . . 106ID Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . 49

MODE:D COMM 2 This parameter defines the data transmission rate for the Port 2 serial communication channel.

Range: 2400, 4800, 9600

Display: PT2 Valu (press • to select, then ENTER)

Reference: Serial Communication Formats . . . . . . . . . . . 49

MODE:D COMM 3 These parameters define the data transmission rate and parity set-ting for the Port 3 serial communication channel.

Range: 4800, 9600, 19k2 (19200)Even, Odd, None

Display: PT3 Valu (press • to select, then ENTER)PT3 Valu (press • to select, then ENTER)


MODE:D COMM 4 These parameters define the data transmission rate and parity set-ting for the Port 4 serial communication channel.

Range: 4800, 9600, 19k2 (19200)Even, Odd, None

Display: PT4 Valu (press • to select, then ENTER)PT4 Valu (press • to select, then ENTER)



Note: This parameter can only be changed via the Engineering Panel.

Computer ID Number

Note: This parameter can only be changed via the Engineering Panel.

Port 2 Baud Rate

Port 3 Baud Rate

Port 3 Parity

Port 4 Baud Rate

Port 4 Parity

September 2005 IM301 (6.1.3)


MODE:D fD 1 This parameter selects the analog input for the flow signal (∆Po) used to compute the mass flow rate (Flow) calculated variable.

Range: Off selects calculated flow measurement1 to 8 selects analog input SV#

Display: fD1 OFF/#

Reference: Displayed Flow. . . . . . . . . . . . . . . . . . . . . . . . 61

MODE:D fD 2 This parameter selects the measured variable for the compensating pressure used to calculate mass flow rates.

Range: 1 to 8 selects analog input MV#

Display: fD2 #

Reference: Compensating Pressure . . . . . . . . . . . . . . . . 59

MODE:D fD 3 This parameter selects the measured variable for the compensating temperature used to calculate mass flow rates.

Range: 1 to 8 selects analog input MV#

Display: fD3 #

Reference: Compensating Temperature . . . . . . . . . . . . . 59

MODE:D fE 1 This parameter determines whether the controller will operate in its redundant mode when its D1 discrete input is asserted.

Range: Off redundant tracking disabledOn redundant tracking enabled

Display: fE1 OFF/ON

Reference: Redundant Tracking. . . . . . . . . . . . . . . . . . . 106

MODE:D LOCK 0 If redundant controllers are given the same Controller ID Number [MODE:D COMM 0], this parameter must be disabled so that only one of them will respond to Modbus data requests to that address. If they are given different ID numbers, enabling this parameter allows the Modbus host to monitor both controllers.

Range: Off host cannot monitor tracking controllerOn host can monitor tracking controller

Display: LOC0 OFF/ON

Reference: Redundant Tracking. . . . . . . . . . . . . . . . . . . 106

Mass Flow Input

CompensatingPressure Input

CompensatingTemperature Input

Redundant Tracking

Modbus While Tracking

September 2005 IM301 (6.1.3)


MODE:D LOCK 1 This parameter and Write Inhibit Only [MODE:D LOCK 2] define the level of access (read/write, read-only, or none) that a host device has to the controller’s Modbus data.

Range: Off access defined by Write Inhibit OnlyOn no Modbus access


Reference: Modbus Configuration . . . . . . . . . . . . . . . . . . 50

MODE:D LOCK 2 If Read and Write Inhibit [MODE:D LOCK 1] is disabled, this param-eter defines the level of access (read/write or read-only) that a host device has to the controller’s Modbus data.

Range: Off read and write accessOn read access only



MODE:D LOCK 3 If this parameter is On, you can alternate between the first and sec-ond alternate parameter sets by asserting and clearing the D7 discrete input.

Range: Off parameter switching disabledOn D7 selects first or second parameter set


Reference: Alternate Parameter Sets . . . . . . . . . . . . . . . 106

MODE:D LOCK 6 This parameter disables the I/O functions of the CPU and Analog PCB Assemblies. This feature is included only as an aid to develop-ing, testing, and demonstrating the controller and should never be enabled in an installed, operating unit.

Range: Off I/O functions enabledOn I/O functions disabled


Reference: Disabling Input Signals . . . . . . . . . . . . . . . . . . 37

Read and Write Inhibit

Write Inhibit Only

Remote ParameterSwitching

Note: In order to alternate between these two parameter sets, LOCK 3 must be enabled in both of them.

CPU Inputs Lockout

Caution:An installed controller should never be operated with any LOCK 6 parameter enabled, as that would prevent it from receiving needed input signals.

September 2005 IM301 (6.1.3)


MODE:D LOCK 7 This parameter determines whether Modbus holding register values transmitted through Port 3 are scaled to their full, maximum range or to a slightly smaller, rounded-off range (minimum to maximum / 1.024), thus providing compatibility with distributed control systems using either scaling convention.

Range: Off the controller uses the maximum rangeOn the controller uses the reduced range



MODE:D LOCK 9 If you use the Front Panel MENU and SCROLL keys to change the variable displayed in the AUX readout, this parameter determines whether it will automatically revert to displaying the controller status:

Range: Off selected display remains until changedOn status display restored after one minute


Reference: Measured Variables . . . . . . . . . . . . . . . . . . . . 41Calculated Variable Displays . . . . . . . . . . . . . 61

MODE:D RA # Each of these parameters selects the conditions under which the corresponding discrete output is triggered. If the assigned function is positive, the relay will be energized when the associated condition exists. If the value is negative, the relay will de-energize.

Range: see Table 3-4

Display: RA#±Valu (press HIGH or LOW to select sign, then press • to select function)

Reference: Discrete Outputs . . . . . . . . . . . . . . . . . . . . . . 45

PID:A G This parameter sets the ramp rate for bumpless transfers and the decay rate for the derivative response.

Range: 0.00 to 9.99 repeats/minute

Display: G #.##

Reference: Derivative Response . . . . . . . . . . . . . . . . . . . 74PI and RT Signal Selection . . . . . . . . . . . . . . 77Antisurge PI Response . . . . . . . . . . . . . . . . . 79Output Tracking . . . . . . . . . . . . . . . . . . . . . . 102Port 1 Balancing. . . . . . . . . . . . . . . . . . . . . . . 94Port 2 Balancing. . . . . . . . . . . . . . . . . . . . . . . 94

Modbus RegisterScaling

Auxiliary Display Reset

Relay AssignedFunction

General Ramp Rate

September 2005 IM301 (6.1.3)


PID:A Kr 1 This parameter sets the reset rate for the antisurge control loop.


Display: Kr1 ##.#

Reference: General PI Algorithm . . . . . . . . . . . . . . . . . . . 78Antisurge PI Response. . . . . . . . . . . . . . . . . . 79

PID:A Kr 2 This parameter sets the reset rate for the discharge pressure limit-ing loop.


Display: Kr2 ##.#

Reference: General PI Algorithm . . . . . . . . . . . . . . . . . . . 78Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . 82

PID:A Kr 3 This parameter sets the reset rate for the suction pressure limiting loop.


Display: Kr3 ##.#


PID:A PB 1 This parameter sets the proportional band coefficient for the anti-surge control loop.

Range: 006 to 999

Display: PB1 ###

Reference: General PI Algorithm . . . . . . . . . . . . . . . . . . . 78Antisurge PI Response. . . . . . . . . . . . . . . . . . 79

PID:A PB 2 This parameter sets the proportional band coefficient for the dis-charge pressure limiting loop.

Range: 006 to 999

Display: PB2 ###


PID:A PB 3 This parameter sets the proportional band coefficient for the suction pressure limiting loop.

Range: 006 to 999

Display: PB3 ###


DEV Reset Rate

Pd Reset Rate

Ps Reset Rate

DEV Proportional Band

Pd Proportional Band

Ps Proportional Band

September 2005 IM301 (6.1.3)


PID:A r 1 This parameter sets the half-width of the antisurge control loop’s dead zone.


Display: r1 ##.#

Reference: Dead Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . 78Antisurge PI Response . . . . . . . . . . . . . . . . . 79

PID:A r 3 This parameter sets the width of the derivative control response’s dead zone.

Range: 00.0 to 99.9 percent / 160 milliseconds

Display: r3 ##.#


PID:A Td 0 This parameter sets the time constant for the derivative control response.


Display: Td0 ##.#


PID:A Td 1 This parameter sets the time constant for the derivative recycle trip response.


Display: Td1 ##.#


PID:A Tf 1 This parameter defines the time constant for the first-order-lag soft-ware filter applied to the numerator and denominator of Ss.


Display: Tf1 ##.#

Reference: Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

PID:A Tf 2 If the selected Application Function [MODE:A fA] calculates the polytropic head exponent (σ), this parameter defines the time con-stant for its first-order-lag software filter.


Display: Tf2 ###

Reference: Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Startup Configuration . . . . . . . . . . . . . . . . . . 104

DEV Dead-Zone Bias

CRD Dead-Zone Bias

CRD Time Constant

Recycle Trip TimeConstant

DEV Filter Constant

Sigma Filter Constant

September 2005 IM301 (6.1.3)


SPEC:A A 1 If Surge Detection Method [MODE:A fD 2] 1, 2, or 3 is selected, this parameter defines its flow rate-of-change limit.

Range: –99.9 to 99.9 percent/160 milliseconds

Display: A1 ##.#


SPEC:A A 2 If Surge Detection Method [MODE:A fD 2] 1 is selected, this param-eter defines the time interval during which the controller will look for a rapid change in flow following a rapid change in pressure.

Range: 0.00 to 9.96 seconds (multiples of .04)

Display: A2 #.##


SPEC:A A 3 If Surge Detection Method [MODE:A fD 2] 1, 2, or 4 is selected, this parameter defines its pressure rate-of-change limit.

Range: –99.9 to 99.9 percent/160 milliseconds

Display: A3 ##.#


SPEC:A A 4 If Surge Detection Method [MODE:A fD 2] 1 is selected, this param-eter defines the time interval during which the controller will look for a rapid change in pressure following a rapid change in flow.


Display: A4 #.##


SPEC:A A 5 This parameter defines how long the controller will wait after detect-ing a surge before looking for another.


Display: A5 #.##


SPEC:A b 1 This parameter defines the initial value of the surge control line bias, prior to adding the Safety On and derivative responses.


Display: b1 ##.#

Reference: Surge Control Line . . . . . . . . . . . . . . . . . . . . . 72Recycle Trip Line . . . . . . . . . . . . . . . . . . . . . . 73Cold-Recycle Control . . . . . . . . . . . . . . . . . . . 95

Flow Rate-of-ChangeThreshold

Flow After PressureTime Lag

Pressure Rate-of-Change Threshold

Pressure After FlowTime Lag

Safety On RepeatInterval

Initial Surge ControlBias

September 2005 IM301 (6.1.3)


SPEC:A b 2 This parameter defines the distance added to the surge control mar-gin every time a surge is detected.


Display: b2 ##.#

Reference: Safety On Response . . . . . . . . . . . . . . . . . . . 75Cold-Recycle Control . . . . . . . . . . . . . . . . . . . 95

SPEC:A b 3 This parameter defines the maximum amount by which the deriva-tive control response will increase the surge control margin.


Display: b3 ##.#

Reference: Derivative Response . . . . . . . . . . . . . . . . . . . 74Cold-Recycle Control . . . . . . . . . . . . . . . . . . . 95

SPEC:A C 0 This parameter defines the gain for the proportional portion of the Recycle Trip step response.

Range: 00.0 to 99.9

Display: C0 ##.#


SPEC:A C 1 This parameter defines the maximum size of the Recycle Trip step response.


Display: C1 ##.#


SPEC:A C 2 This parameter defines the time interval between Recycle Trip step responses.

Range: 0.04 to 9.96 seconds (multiples of 0.04)

Display: C2 #.##


SPEC:A C 3 If Application Function [MODE:A fA] 34, 35, or 64 is selected, the combined flow calculation multiplies this controller’s sidestream flow by this coefficient.

Range: 0.00 to 9.99

Display: C3 #.##

Reference: Upstream Section Flow Known . . . . . . . . . . . 87Downstream Section Flow Known . . . . . . . . . 89

Safety On IncrementalBias

Maximum DerivativeResponse

Recycle Trip Gain

Maximum Recycle TripStep Size

Recycle Trip RepeatInterval

Sidestream FlowCoefficient

September 2005 IM301 (6.1.3)


SPEC:A C 4 If Application Function [MODE:A fA] 34, 35, or 64 is selected, the combined flow calculation multiplies the reported flow of the Adja-cent Section Controller [MODE:A SS 5] by this coefficient.

Range: 0.00 to 9.99

Display: C4 #.##


SPEC:A C 5 If Application Function [MODE:A fA] 34, 35, or 64 is selected, the combined flow calculation multiplies the square root of the compo-nent flows’ product by this coefficient.

Range: –9.99 to 9.99

Display: C5 #.##


SPEC:A d 1 This parameter defines the offset between the tight shut-off line and the surge control line.


Display: d1 ##.#

Reference: Tight Shut-Off Line . . . . . . . . . . . . . . . . . . . . . 74Tight Shut Off Response . . . . . . . . . . . . . . . 101

SPEC:A K This parameter defines the constant that the controller uses to nor-malize the Ss proximity-to-surge variable.

Range: .000 to .999

Display: K .###

Reference: Discharge Flow Measurement . . . . . . . . . . . . 57Application Function . . . . . . . . . . . . . . . . . . . . 63Valve-Sharing Fallback. . . . . . . . . . . . . . . . . . 70

SPEC:A RT This parameter defines the initial bias used to calculate the margin between the Recycle Trip and surge limit lines when the surge count is zero. An additional bias is added each time a surge is detected.


Display: RT ##.#

Reference: Recycle Trip Line . . . . . . . . . . . . . . . . . . . . . . 73Dead Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Main Flow Coefficient

Combined FlowCoefficient

Tight Shut-Off LineDistance

Surge Limit LineCoefficient

Recycle Trip LineDistance

September 2005 IM301 (6.1.3)


SPEC:A SO This parameter defines the bias used to calculate the margin between the Safety On and surge limit lines.


Display: SO ##.#

Reference: Safety On Line . . . . . . . . . . . . . . . . . . . . . . . . 73

SPEC:A TL This parameter defines the time constant for the exponential decay of the Recycle Trip response.


Display: TL ###


Safety On LineDistance

Recycle Trip DecayRate

September 2005 IM301 (6.1.3)



Appendix B Controller Test SequencesThis appendix describes the controller test procedures that can be executed from the Engineering Panel.

Each such key sequence begins with a data group key that selects the function of the second key. Unlike configuration sequences, most of these procedures are not assigned to specific data pages, so a data page letter (for example, MODE:D ANIN –) is indicated only if you must press the data group key as many times as needed to display that letter at the end of the first step confirming display.

Pressing the CLEAR key will terminate any of these procedures and clear the display. Otherwise, they time out and automatically clear the display after 45 seconds of keyboard inactivity.

MODE:D ANIN – This procedure can be used to identify which analog input signal(s) triggered a transmitter alarm. To initiate it, press the following keys:

repeat until you see

or

or

The digit in this display is the analog input channel number (AN1). HIGH indicates that signal is above its Analog Input High Alarm Limit, LOW indicates it is below its Analog Input Low Alarm Limit, or GOOD indicates it is between those limits. The status of the dis-played input is updated continuously.

You can determine the status of each consecutive input signal by pressing the • key:

or

or

This allows you to repetitively cycle through all the inputs.

Transmitter Status Test

MODE MODE: D

AN IN–

AN1 GOOD

AN1 HIGH

AN1 LOW

•

AN2 GOOD

AN2 HIGH

AN2 LOW

September 2005 IM301 (6.1.3)

140

Appendix B: Controller Test Sequences

MODE COMM To restart the control program (see MODE TEST 6 on page 146), press the following keys:

MODE COMM – 2 To determine if the controller has detected any Port 2 serial commu-nications activity within the past second, press the following keys:

or

where the confirming display will be GOOD if a serial transmission has been received during the previous second.

MODE COMM – 3 To identify the companion controllers from which Port 1 transmis-sions are being received, press the following keys:

or

where the digit is a controller ID number. GOOD indicates data is being received from that controller, BAD indicates it is not. Subse-quently pressing the decimal key displays the same information for the next possible companion controller. You can cycle through all eight possible IDs (including this controller’s own) by repeatedly pressing that key. The status of controller 1 will be displayed if you press that key while viewing the status of controller 8:

Reset Controller

MODE COMM ENTER Reset

Serial Port 2 Test

MODE COMM– 2

-2 GOOD

-2 BAD

Note:

This port is used primarily for load-sharing and performance over-ride control. If either of these features is being used, a BAD result for this test usually indicates a serious problem. If they are not being used, Port 2 is usually not even connected to any other controllers and a BAD result is of no consequence.

Serial Port 1 Test

MODE COMM– 3

-1 GOOD

-1 BAD

•

-8 BAD

•

-1 GOOD

Note:

Although transmissions are normally received from all controllers connected to Port 1 (including this one), only those from specified companion controllers are normally of any concern.

September 2005 IM301 (6.1.3)


MODE LOCK 3 •

This procedure copies the controller’s current parameters into any of its three alternate sets.

To initiate this procedure, which you can abort at any time by press-ing CLEAR, press the following keys:

This display indicates which alternate set the current parameters will be copied into. To select a different set, press the decimal (•) key:

Pressing ENTER will then copy the current parameters to the indi-cated alternate set and briefly display that set’s new checksum:

MODE LOCK 3 • •

This procedure copies any of the three alternate parameter sets into the controller’s current set.

To initiate this procedure, which you can abort at any time by press-ing CLEAR, press the following keys:

This display indicates which alternate set will be copied into the working memory. To select a different set, press the decimal (•) key:

Pressing ENTER will then initiate a recall of the selected alternate parameter set. If it is valid, it is copied into the current set and the controller executes a soft reset. If the selected set is invalid (which probably means it was never defined), “No Match” is displayed to inform you that the recall has been aborted:

or

Store AlternateParameters

MODE LOCK3 •

ENTER Store1?

•

Store2?

ENTER CS= F882

Recall AlternateParameters

MODE LOCK3 • •

ENTER Recall1?

•

Recall2?

ENTER Reset

No Match

September 2005 IM301 (6.1.3)

142


MODE LOCK 4 This procedure displays the checksum values of the controller’s various parameter sets. You can determine which (if any) of the alternate parameter sets is currently in use by comparing the check-sum of the Present and Long-Term sets to those for the alternate sets. You can also tell if any of these parameter sets agree with those recorded on a parameter worksheet by comparing these checksums to those recorded on that worksheet.

To view the parameter checksums, press the following keys:

or

If the confirming display beings with CS, the present parameter set is the same as that stored in long-term memory. If that display begins with P, the two sets differ and the checksum shown is for the present set. In that case, you can display the long-term parameter checksum by pressing the decimal key:

If the two parameter sets are different, you should use the Disable Reconfiguration [MODE LOCK 5 0] procedure to disable reconfigu-ration. The controller will then correct any errors that occur in the present parameter set.

To display the Alternate Parameter Set checksums, continue to press the decimal (•) key:

You can cycle through the displays of all four (or five) checksums by continuing to press the decimal (•) key as many times as you want.

Parameter Checksum

MODE LOCK4

CS= F882

P = A76F

•

L = A3C2

•

CS1=B94A

•

CS2=632E

•

CS3=44FC

September 2005 IM301 (6.1.3)


MODE LOCK 5 1 To enable alteration of the controller’s configuration and tuning parameters from the Engineering Panel, press the following keys:

If you make a mistake entering this sequence, the controller will beep and display an Error! message on the confirming display.

When you finish reconfiguring your controller, enter the Disable Reconfiguration [MODE LOCK 5 0] sequence to disable further changes (otherwise, reconfiguration will be automatically disabled after thirty minutes of keyboard inactivity):

MODE LOCK 5 0 To disable alteration of the controller’s configuration and tuning parameters from the Engineering Panel, press the following keys:

If you make a mistake entering this sequence, the controller will beep and display an Error! message on the confirming display.

MODE TEST To initiate a Recycle Trip Response (see page 80), press the follow-ing keys:

By analyzing the resulting behavior of your process, you can deter-mine if that control response is optimally tuned for your application.

Enable Reconfiguration

MODE LOCK5 1

LOC5 ON

ENTER

DisableReconfiguration

MODE LOCK5 0

LOC5 OFF

ENTER

Force Recycle Trip

MODE TEST TEST

ENTER

Note:

This test is not a self-test of the controller. It merely triggers a Recy-cle Trip response so you can observe how your process responds. This test can only be performed while the controller is in automatic.

September 2005 IM301 (6.1.3)

144


MODE TEST 2 To determine which revision of the control program is installed in your controller, press the following keys:

which displays the controller’s software version number.

MODE TEST 3 To view a dynamic display of a specified serial port’s communica-tions activity, press the following keys:

where # is the numeric key corresponding to the port number. The bar after the R will be in the high position if that port is currently receiving a transmission, otherwise it will be low. Similarly, the bar after the T will be high only when that port is transmitting. The port in the above example is receiving but not transmitting.

You can then check for communications activity on any other port by pressing the corresponding numeric key (for example, press 4 to view Port 4’s activity):

MODE TEST 4 This procedure displays the values of the analog and discrete input signals and the positions of the front-panel Control Keys. To initiate it, press the following keys:

To display the measured value of any analog input, press the corre-sponding numeric key. For example, pressing 1 displays the current value of the CH1 input:

where the number in the display is the corresponding signal variable (values above 99.9 percent display as A0.0). Thus, you can deter-mine if an input is being read accurately by disabling its Offset Zero Input [MODE:D ANIN #] parameter and comparing the resulting TEST 4 value to a volt or ammeter measurement of the correspond-ing input signal. Alternately, you can display the value of each consecutive analog input by pressing the decimal key (•).

Program Version

MODE TEST2

756-001

Serial Port Activity Test

MODE TEST3 #

PT# R-T_

4

PT4 R-T_

Signal Values Test

MODE TEST4

Inputs³³

1

CH1 45.8

September 2005 IM301 (6.1.3)


To determine the status of the discrete inputs, press zero (0):

Each character will be the input number if that input is asserted or an underscore if it is not. In the above example, only inputs D2 and D5 are asserted.

To determine which discrete outputs are energized, press nine (9):

where each character will be either the relay number (if that relay is energized) or an underscore or (if it is not). In the above example, only relays CR1 and CR4 are energized.

To determine which front-panel keys are being pressed, press the minus (–) key:

where each character in the confirming display is an underscore if the corresponding key is not pressed, or the key number if it is:

As shown above, only keys 2 (DISPLAY SURGE COUNT) and 5 (SCROLL) are being pressed. This feature is used mostly to deter-mine whether any of these keys are stuck down.

0

_2__5___

9

1__4____

–

_2__5___

COMPRESSOR

4

3

1

2

7

8

6

5

September 2005 IM301 (6.1.3)

146


MODE TEST 6 Resetting the main CPU restarts its control program. This occurs when the controller is powered up, a fault causes a watchdog time out, critical parameters are changed or alternate parameter sets are recalled, the controller is reconfigured from a workstation, or the Reset Controller [MODE COMM] procedure is executed. The result-ing procedure checks the controller’s parameters to make sure they are reasonable, resets its serial ports and analog inputs, and begins a new scan cycle. It does not change the operating state or outputs.

To display the number of times the control program has restarted since this count was last zeroed, press the following keys:

where #### is the reset count, which can then be reset by pressing the zero key:

MODE TEST 7 To display the number of times the front-panel microprocessor has reset since this count was last zeroed, press the following keys:

where #### is its current value, which can then be reset by pressing the zero key:

MODE TEST 8 This procedure initiates the calculation and display of a four-digit, hexadecimal checksum for the controller’s internal binary operating instructions. It is used primarily to verify the successful downloading of a new control program.

To initiate this test, press the following keys. The checksum will be displayed after a brief pause:

where #### is the checksum for the installed software. The Series 3 Plus Antisurge Controller Revision History [DS301/V] provides the correct CRCs for various software revisions.

CPU Reset Count

MODE TEST6

Z80 ####

0

Z80 0000

Front-Panel ResetCount

MODE TEST7

Mot ####

0

Mot 0000

Program Checksum

MODE TEST8

CRC BusY

CRC ####

September 2005 IM301 (6.1.3)


PID:A Td 0 • This procedure displays and can clear the maximum rate-of-change of the Ss proximity-to-surge variable (that is, the fastest approach to surge) that has been detected since this value was last reset. It is an extension of the sequence for viewing and changing the CRD Time Constant [PID:A Td 0], is scaled to the same units (percent of span per 160 milliseconds) as that parameter, and will be valid only if the Derivative Response [MODE:A fC 3] or Derivative Recycle Trip [MODE:A fC 4] is enabled.

To view this derivative, first display the CRD Time Constant. You can then alternate between displaying that parameter and the maximum derivative of Ss by pressing the decimal key:


where Td0 ##.# is the parameter value and Sdt ##.# is the highest recorded derivative. Pressing the zero key while the derivative is displayed resets it to zero:

Because the displayed derivative is immediately updated whenever a faster approach to surge is detected, it will then increase from zero as soon as the operating point moves toward the surge limit. Thus, you can determine the current rate-of-approach to surge by clearing this value and observing the resulting new maximum.

Entering a new CRD Time Constant (by pressing the corresponding numeric keys and ENTER while it is displayed) will terminate this procedure, as will pressing CLEAR at any time.

Maximum Ss Derivative

PID PID: A

Td 0

Td0 ##.#

•

Sdt ##.#

•

Td0 ##.#

Sdt ##.#0

Sdt 00.0

September 2005 IM301 (6.1.3)

148 Appendix B: Controller Test Sequences

SPEC:A A 1 • This procedure displays and can clear the highest positive and low-est negative derivatives of SV1 (which is generally the unscaled flow measurement) that have been detected since they were last reset. It is an extension of the sequence for viewing and changing the Flow Rate-of-Change Threshold [SPEC:A A 1], is scaled to the same units (percent of span per 160 milliseconds), and will be valid only if a Surge Detection Method [MODE:A fD 2] that monitors SV1 has been selected [fD 2 = 1, 2, or 3].

To view these derivatives, first display the Flow Rate-of-Change Threshold. You can then cycle between displaying that parameter and the derivatives of SV1 by pressing the decimal key:


where A1 ##.# is the parameter value, A1H ##.# is the most positive derivative, and A1L–##.# is the most negative. The derivatives are immediately updated if faster rates-of-change are detected. Press-ing the zero key while either derivative is displayed resets it to zero:

or

Entering a new Flow Rate-of-Change Threshold (by pressing the corresponding numeric keys and ENTER while it is displayed) will terminate this procedure, as will pressing CLEAR at any time.

Maximum FlowDerivatives

Note: Because these are derivatives of the CH1 signal variable, they are not affected by its process variable gain and bias.

SPECRESP SPEC: A

A 1

A1 ##.#

•

A1H ##.#

•

A1L-##.#

•

A1 ##.#

0

A1H 00.0

0

A1L 00.0

September 2005 IM301 (6.1.3)


SPEC:A A 3 •

This procedure displays and can clear the highest positive and low-est negative derivatives of SV2 (which is generally the unscaled discharge pressure measurement) that have been detected since they were last reset. It is an extension of the sequence for viewing and changing the


[SPEC:A A 3], is scaled to the same units (percent of span per 160 millisec-onds), and is valid only if a

Surge Detection Method

[MODE:A fD 2] that monitors SV2 has been selected [fD 2 = 1, 2, or 4].

To view these derivatives, first display the


. You can then cycle between displaying that parameter and the derivatives of SV2 by pressing the decimal key:


where

A3 ##.# is the parameter value, A3H ##.# is the most positive derivative, and A3L–##.# is the most negative. The derivatives are immediately updated if faster rates-of-change are detected. Press-ing the zero key while either derivative is displayed resets it to zero:

or

Entering a new Pressure Rate-of-Change Threshold (by pressing the corresponding numeric keys and ENTER while it is displayed) will terminate this procedure, as will pressing CLEAR at any time.

Maximum PressureDerivatives

Note: Because these are derivatives of the CH2 signal variable, they are not affected by its process variable gain and bias.

SPECRESP SPEC: A

A 3

A3 ##.#

•

A3H ##.#

•

A3L-##.#

•

A3 ##.#

0

A3H 00.0

0

A3L 00.0

September 2005 IM301 (6.1.3)

150 Appendix B: Controller Test Sequences

September 2005 IM301 (6.1.3)



Appendix F Application FunctionsThis appendix describes each fA mode of the standard Antisurge Controller that is currently recommended for general use, including:

• the coordinate system and algorithm it uses to compute proxim-ity-to-surge (Ss),

• the process variables it requires and the inputs it usually obtains them from,

• a simplified process and instrumentation drawing (P&ID) of the interface between the controller and compressor (a question mark indicates a variable can be assigned to any appropriate or otherwise unused channel), and

• a discussion of applicable fallback strategies.

Table F-1 Analog inputs required by each fA Mode

fA CH1 CH2 CH3 CH4 1 CH5 CH6 CH7 2

01 ∆Po ∆Pc

02 3 ∆Po ∆Pc

31 ∆Po Pd Ps

33 3 ∆Po Pd Ps

34 ∆Po,ss Pd Pss N Ps–

35 ∆Po,ss Pss Ps N

51 J 4 Pd Ps N

61 3 ∆Po,s Pd Ps

63 3,5 ∆Po,d Pd Ps Td Ts

65 3,5 ∆Po,s Pd Ps Td Ts

67 3,5 ∆Po,d Pd Ps Td Ts

68 3,5 ∆Po,ac Pd Ps Td Ts Tac

1 CH4 is normally a speed input but can be assigned another func-tion if an analog speed signal is not required.

2 CH7 is the low flow or valve position input and CH8 is the output loopback input, although either can be given other functions.

3 Optional f5 argument (U5) can be assigned any input.4 Suggested input for an assignable signal.5 Temperature inputs are not required if the Constant Sigma

[MODE:A fC 2] option is enabled.

September 2005 IM301 (6.1.3)

152 Appendix F: Application Functions

Mode fA 00 Cold Recycle Control

As described on page 95, this mode calculates proximity to surge as the highest S (lowest DEViation) reported by any specified Valve Sharing Companion [MODE:A SS 1 #]:

Fallback Strategies: If fA 00 is selected, the only applicable fallback is fD 31.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller fails to receive a valid proximity to the surge control line variable (S) from one or more companion controllers, or if one or more of those controllers has fallen back to fD 31. It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].

FT

UIC FY

PT

Pd∆Po

1 23

PT

Ps

Ss,1

1

FT

UIC FY

PT

Pd∆Po

1 23

PT

Ps

Ss,2

2

FY

UIC3

Ss max Si( )=

September 2005 IM301 (6.1.3)


Mode fA 01 Pressure Rise / Orifice Pressure Drop

This mode calculates proximity to surge as:

where:

∆Pc = differential pressure rise (PV2)

∆Po,c = Calculated Flow Measurement (PV1)

K = Surge Limit Line Coefficient [SPEC:A K]

It is intended for low compression ratio applications, in which the non-characterized ratio of the compression ratio to the squared reduced flow sometimes provides adequate surge protection:

The flow measurement can be the pressure drop across an orifice in either suction or discharge. It can be compensated for the presence of a valve between the orifice and compressor by connecting an ori-fice pressure signal to the Flow Element Pressure Input [MODE:A SS 8] and a pressure signal from the compressor side of the valve to analog input CH3:

where n is the value of SS 8.

If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its ∆Po,c to its companion controllers.

FT

UIC FY

DPT

∆Pc∆Po

1 2

Note: Flow can be measured in discharge

Ss

K Pc∆⋅Po c,∆

------------------=

Ss

K Rc 1–( )⋅

qs2

-----------------------------K Pd Ps–( ) Ps⁄⋅

Po∆ Ps⁄-------------------------------------------

K Pc∆⋅

Po∆------------------= = =

Po c,∆ PV1 PVn PV3⁄( )⋅=

September 2005 IM301 (6.1.3)


Alternate Applications: In essence, this algorithm characterizes the surge limit as a propor-tional relationship between the scaled values of two analog inputs:

It can thus be used to implement a variety of proximity to surge approximations that have this general form. For example, discharge pressure versus a discharge or suction flow measurement (Pd / ∆Po,d or Pd / ∆Po,s) or suction pressure versus a discharge or suc-tion flow measurement (Ps / ∆Po,d or Ps / ∆Po,s)

Fallback Strategies: If fA 01 is selected, the applicable fallbacks are fD 31, 32, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its flow input (CH1). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].

If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the flow input is good but the pressure input is not. The con-troller then falls back to minimum flow control, using the Default Minimum Flow [COND:A CONST 2] as its set point:

If fD 32 is disabled, any condition that would otherwise trigger it will instead trigger the Default Output Fallback.

If the Valve Sharing Fallback [MODE:A fD 3 8] is enabled for a pri-mary Valve Sharing controller, the controller will use the Alternate K [COND:A CONST 8] if it fails to receive Port 1 transmissions from any designated companion controller:

SsK PV2⋅

PV1--------------------=

SsConst 2

Po c,∆--------------------=

Ss

Const 8 Pc∆⋅Po c,∆

-----------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 02 Pressure Rise / Orifice Pressure Drop, with General Characterizer


where:

∆Pc = differential pressure rise (PV2)





It is intended for low compression ratio applications, in which the non-characterized ratio of the compression ratio to the squared reduced flow can sometimes provide adequate surge protection:

The General Characterizer [COND:A f(X) 5 # and X 5 #] can then further define that limit as a function of a secondary coordinate specified as the f5 Argument [MODE:A SS 9]. Guide vane angle is perhaps the most common secondary coordinate, as shown in the accompanying P&ID.

The flow measurement can be the pressure drop across an orifice in either suction or discharge. It can be compensated for the presence of a valve between the orifice and compressor by connecting an ori-fice pressure signal to the Flow Element Pressure Input [MODE:A

UIC FY

∆Pc∆Po

1 2


?

FT DPTZT

α

Ss

K Pc∆ f5 U5( ) f3 N( )[ ]⋅ ⋅ ⋅Po c,∆

------------------------------------------------------------=

Ss

K Rc 1–( )⋅

qs2

-----------------------------K Pd Ps–( ) Ps⁄⋅

Po∆ Ps⁄-------------------------------------------

K Pc∆⋅

Po∆------------------= = =

September 2005 IM301 (6.1.3)


SS 8] and a pressure signal from the compressor side of the valve to analog input CH3:


Although the X Coordinate Characterizer [COND:A f(X) 3 # and X 3 #] should be defined as a constant, it is none-the-less advisable to define a speed source. To use analog input CH4 (as indicated), set the Rotational Speed Source [MODE:A ANIN 4] to Off. Alternately, you can obtain that variable from a companion Speed or Fuel Con-troller by setting that parameter equal to its Controller ID Number.

If calculation of the Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its ∆Po,c to its companions.

Alternate Applications: In essence, this algorithm characterizes the surge limit as a propor-tional relationship between the scaled values of two analog inputs:

It can thus be used to implement a variety of proximity to surge approximations that have this general form. For example, discharge pressure versus a discharge or suction flow measurement (Pd / ∆Po,d or Pd / ∆Po,s) or suction pressure versus a discharge or suc-tion flow measurement (Ps / ∆Po,d or Ps / ∆Po,s)

Fallback Strategies: If fA 01 is selected, the applicable fallbacks are fD 31, 32, 35, 36, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its flow input (CH1). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].

If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the flow input is good but the pressure or secondary coordi-nate input (CH2) is not. The controller then falls back to minimum flow control, using the Default Minimum Flow [COND:A CONST 2] as its set point:

If fD 32 is disabled, conditions that would otherwise trigger it will invoke the Default Output Fallback instead.

If enabled, the Speed Fallback [MODE:A fD 3 5] causes the control-ler to use the Default Speed [COND:A CONST 5] when it detects the loss of the speed signal:

Po c,∆ PV1 PVn PV3⁄( )⋅=

SsK PV2⋅

PV1--------------------=

SsConst 2

Po c,∆--------------------=

Ss K Pc∆ f5 U5( ) f3 Const 5( )⋅ ⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)


If fD 35 is disabled, failure of the speed signal will instead trigger the Minimum Flow Fallback.

If enabled, the Function 5 Fallback [MODE:A fD 3 6] causes the controller to use the Default f5 Argument [COND:A CONST 6] when it detects the failure of the analog input specified as the f5 Argument:

If fD 36 is disabled, failure of the f5 Argument input will trigger the Minimum Flow Fallback.

Note:If f3 is defined as a constant (so rotational speed has no effect on S), fD 35 should be enabled. Otherwise, failure of the speed input would unnecessarily trigger the minimum flow fallback.

Ss K Pc∆ f5 Const 6( ) f3 N( )⋅ ⋅ ⋅ Po c,∆⁄=

Note:If you define f5 as a constant, so that its argument has no effect on the value of S, the f5 Argument should be an input that can be con-figured to always be valid (by setting the alarm limits to 00.0 and 102.4). If that is not possible, enable fD 36 so a failure of the f5 input would not unnecessarily trigger the minimum flow fallback.

September 2005 IM301 (6.1.3)


Mode fA 31 Compression Ratio / (Reduced Flow = ∆Po/Ps)2


where:


f1(Rc) = Y Coordinate Characterizer


Pd = Discharge Pressure (PV2)

Ps = Suction Pressure (PV3)


The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced flow) as a function of the compression ratio.

The flow measurement can be the differential pressure drop across an orifice in either suction or discharge. It can be obtained from a specified Adjacent Section Controller [MODE:A SS 5], but is usually the CH1 analog input [SS 5 Off].

Suction flow measurements can be compensated for the presence of a valve between the orifice and compressor inlet by designating a Flow Element Pressure Input [MODE:A SS 8]:

where n is the value of SS 8. If flow is measured in discharge, that parameter should be disabled.

FT

UIC FY

Pd∆Po

3 2

PT

Ps

PT

1


Ss

K f1 Rc( ) Ps⋅ ⋅Po c,∆

---------------------------------=

Po c,∆ PV1 PVn Ps⁄( )⋅=

September 2005 IM301 (6.1.3)


If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will use its Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #] to compute the ∆Po,r it reports to its companion control-lers from its calculated flow measurement:

When this controller uses the flow measurement the other controller needs, f2 should be set so that it always returns a value of one.

When this controller uses a ∆Po,s and the other controller needs ∆Po,d, f2 should be configured as:

where:

σ = polytropic head exponent

When this controller uses ∆Po,d and the other controller needs ∆Po,s, f2 should be configured as:

Fallback Strategies: If fA 31 is selected, the potentially applicable fallbacks are fD 31, 32, 33, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its flow input (SS 5 Off) or fails to receive a reported flow measurement for the adjacent com-pressor section (1 ≤ SS 5 ≤ 8). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recy-cle [COND:A CONST 1].

If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the flow input is good but the suction pressure input (CH3) is not. The controller then falls back to minimum flow control, using the Default Minimum Flow [COND:A CONST 2] as its set point:

If ∆Pc Substitution [MODE:A SS 6 1] has been set to LOW, thus enabling calculation of Ps from Pd and ∆Pc, the failure of either pres-sure input would prevent the calculation of Ps and would therefore trigger this fallback. If fD 32 is disabled, any condition that would otherwise trigger it will instead trigger the Default Output Fallback.

If enabled, the Compression Ratio Fallback [MODE:A fD 3 3] causes the controller to use the Default Compression Ratio [COND:A CONST 3] if the discharge pressure input (CH2) fails:

Po r,∆ Po c,∆ f2 Rc( )⋅=

Po d,∆ Po s,∆ f2 Rc( )⋅= f2 X( ) xσ 1–=

Po s,∆ Po d,∆ f2 Rc( )⋅= f2 X( ) x1 σ–=

Ss Const 2 Po c,∆⁄=

Ss K f1 Const 3( ) Ps⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)


If fD 33 is disabled, the failure of either pressure input will trigger the Minimum Flow Fallback.


Ss Const 8 f1 Rc( ) Ps⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)


Mode fA 33 Compression Ratio/(Reduced Flow = ∆Po/Ps)2, with General Characterizer

This mode, which does not assume constant molecular weight, cal-culates proximity to surge as:

where:






N = Rotational Speed (PV4)




The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced flow) as a function of the compression ratio. The General Characterizer [COND:A f(X) 5 # and X 5 #] can then further define that limit as a function of a sec-ondary coordinate specified as the f5 Argument [MODE:A SS 9]. Guide vane angle is perhaps the most common secondary coordi-nate, as shown in the accompanying P&ID.

The flow measurement can be the differential pressure drop across an orifice in either suction or discharge. It can be obtained from a

FT

UIC FY

ZT

Pd∆Po

2?

PT

Ps

PT

4

α


31

ST

N

Ss

K f1 Rc( ) f5 U5( ) Ps f3 N( )[ ]⋅ ⋅ ⋅ ⋅Po c,∆

---------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)


specified Adjacent Section Controller [MODE:A SS 5], but is usually the CH1 analog input [SS 5 Off].

Suction flow measurements can be compensated for the presence of a valve between the orifice and compressor inlet by designating a Flow Element Pressure Input [MODE:A SS 8], and connecting an appropriate pressure signal to that input:



If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will use its Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #] to compute the ∆Po,r it reports to its companion control-lers from its calculated flow measurement:

When this controller uses the flow measurement the other controller needs, f2 should be set so that it always returns a value of one.

When this controller uses a ∆Po,s and the other controller needs ∆Po,d, f2 should be configured as:

where:

σ = polytropic head exponent

When this controller uses ∆Po,d and the other controller needs ∆Po,s, f2 should be configured as:


Po r,∆ Po c,∆ f2 Rc( )⋅=

Po d,∆ Po s,∆ f2 Rc( )⋅= f2 X( ) xσ 1–=

Po s,∆ Po d,∆ f2 Rc( )⋅= f2 X( ) x1 σ–=

September 2005 IM301 (6.1.3)


Fallback Strategies: If fA 33 is selected, the potentially applicable fallbacks are fD 31, 32, 33, 35, 36, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its flow input (SS 5 Off) or fails to receive a reported flow measurement for the adjacent com-pressor section (1 ≤ SS 5 ≤ 8). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recy-cle [COND:A CONST 1].









Ss K f1 Const 3( ) f5 U5( ) Ps f3 N( )⋅ ⋅ ⋅ ⋅ Po c,∆⁄=

Ss K f1 Rc( ) f5 U5( ) Ps f3 Const 5( )⋅ ⋅ ⋅ ⋅ Po c,∆⁄=


Ss K f1 Rc( ) f5 Const 6( ) Ps f3 N( )⋅ ⋅ ⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)





Ss Const 8 f1 Rc( ) Ps f5 U5( )⋅ ⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)


Mode fA 34 Compression Ratio/(Reduced Flow)2, for combined upstream and sidestream flows

This mode is for compressor sections with no total flow measure-ment, assumes all streams have the same molecular weight, and calculates proximity to surge as:

where:







Pss = sidestream pressure (PV3)

Rc = Compression Ratio (Pd/Pss)


Ps–

FT

FY

Recycle

Section 2 Section 1 Section 3

UIC

N1

SIC

Pd

FT

Pss

PT PT

UIC

∆Po,ss 1 23

52

Speed signal can be analog or serial

4

ST

N

Note: Drawing shows only the transmitters and control elements required by UIC 2

PT

Po r,–∆

Po s,–∆

or Sidestream

Ss

K f1 Rc( ) Pss f3 N( )[ ]⋅ ⋅ ⋅Po c,∆

-----------------------------------------------------------=

September 2005 IM301 (6.1.3)


The flow measurement (∆Po,c) is calculated as an equivalent differ-ential pressure drop across an orifice in suction (∆Po,s):

where:




= equiv. upstream section discharge flow measurement

= reported upstream section flow measurement

= suction sidestream flow measurement (PV1)

f2() = Reported Flow Characterizer

= suction pressure of preceding section (PV5)

is received via Port 1 serial communications from the Anti-surge Controller identified as the Adjacent Section Controller [MODE:A SS 5]. The Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #] is then used to calculate an equivalent differential pressure drop across an orifice in that section’s discharge:

• If that section’s controller is configured to report its discharge flow measurement, this controller’s f2 should be defined as a constant and the (PV5) input is not needed.

• If that controller is configured to report its suction flow measure-ment, this controller’s f2 should be defined as:

where:

σ– = upstream section polytropic head exponent

The sidestream flow measurement can be compensated for the presence of a valve between the orifice and compressor by desig-nating a Flow Element Pressure Input [MODE:A SS 8]:


If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its ∆Po,c to its companion controllers.

Po c,∆ C3 Po ss,∆⋅ C4 Po d,–∆⋅ C5 Po ss,∆ Po d,

–∆⋅+ +=

Po d,–∆ Po r,

–∆ f2 Pss Ps–⁄( )⋅=

Po d,–∆

Po r,–∆

Po ss,∆

Ps–

Po r,–∆

Ps–

Po d,–∆ Po s,

–∆ f2 Rc–

( )⋅= f2 X( ) xσ– 1–=

Po ss,∆ PV1 PVn Pss⁄( )⋅=

Note:The Adjacent Section Controller must be configured to report a flow measurement (∆Po) rather than a mass flow (W2), usually by select-ing an fA mode between 31 and 34.

September 2005 IM301 (6.1.3)



Fallback Strategies If fA 34 is selected, the potentially applicable fallbacks are fD 31, 32, 33, 35, 37, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its sidestream flow (CH1) or previous section suction pressure (CH5) input, or fails to receive a valid reported flow measurement for the adjacent compressor sec-tion (if serial communication fails or that controller has fallen back to fD 31). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].

If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the flow input is good but the sidestream pressure input (CH3) is not. The controller then falls back to minimum flow control, using the Default Minimum Flow [COND:A CONST 2] as its set point. Assuming this input would fail low, its loss would also drive the argu-ment of the Reported Flow Characterizer to zero:

Thus, COND:A f(X) 2 0 should be given a worst-case value that can be calculated as:

If ∆Pc Substitution [MODE:A SS 6 1] has been set to LOW, thus enabling calculation of Pss from Pd and ∆Pc, the failure of either pressure input would prevent the calculation of Pss and would there-fore trigger this fallback. If fD 32 is disabled, any condition that would otherwise trigger it will instead trigger the Default Output Fallback.



Ss Const 2 Po s,∆⁄=

Po s,∆ C3 Po ss,∆⋅ C4 Po d,–∆⋅ C5 Po ss,∆ Po d,

–∆⋅+ +=

Po d,–∆ Po s,

–∆ f2 0( )⋅=

f2 0( ) Po d,–∆ Po s,

–∆⁄( )min=

Ss K f1 Const 3( ) Ps f3 N( )⋅ ⋅ ⋅ Po s,∆⁄=

September 2005 IM301 (6.1.3)




If the Adjacent Section Flow Fallback [MODE:A fD 3 7] is enabled, the flow measurement will be calculated from a Default Adjacent Section Flow [COND:A CONST 7] if the controller fails to receive a flow measurement for the adjacent compressor section:

However, the resulting flow measurement will be used for control purposes only if fD 31 is disabled.


Ss K f1 Rc( ) Ps f3 Const 5( )⋅ ⋅ ⋅ Po s,∆⁄=


Po d,–∆ CONST 7 f2 Ps Ps

–⁄( )⋅=

Ss Const 8 f1 Rc( ) Ps f3 N( )⋅ ⋅ ⋅ Po s,∆⁄=

September 2005 IM301 (6.1.3)


Mode fA 35 Compression Ratio/(Reduced Flow)2, for combined downstream and sidestream flows

This mode, which is for compressor sections that have no total flow measurement, assumes the molecular weight of all streams are equal. It calculates proximity to surge as:

where:

∆Po,r = Reported Flow measurement






Pss = sidestream pressure (PV2)

Rc = Compression Ratio (Pss/Ps)


This section’s reported flow measurement (∆Po,r) is calculated by applying this controller’s Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #] to its equivalent discharge flow measurement (∆Po,d).

Recycle or Sidestream

∆Po,ss

FT

UICN

∆Po,dPs

Section N-1 Section N

PT

SIC

PT

Pss

FT

UIC3

2

4N–1

Speed signal can be analog or serial

ST

Note: Drawing shows only the transmitters and control elements required by UIC N–1

FY

1

Po r,+∆ Po s,

+∆=

Ss

K f1 Rc( ) Ps f3 N( )[ ]⋅ ⋅ ⋅Po r,∆

--------------------------------------------------------=

September 2005 IM301 (6.1.3)


That measurement is in turn calculated from a mass balance over the flows entering the next compressor section:

where:




= reported suction flow measurement from the Antisurge Controller for the downstream section

= discharge sidestream flow measurement (PV1)

= Reported Flow Characterizer

is received via Port 1 communications from the Adjacent Sec-tion Controller [MODE:A SS 5]. If Series Load Variable [MODE:A fC 9] is disabled, a controller using this fA mode will report its ∆Po,r to its companion controllers.

If no other controller needs this controller to report the suction flow for its section, f1 can define the minimum discharge flow measure-ment and f2 can be defined as a constant.

If another controller does need this controller to report its section’s suction flow measurement, f2 must be set up to calculate that flow from the calculated ∆Po,d and f1 should define the minimum suction flow measurement:

where:

σ = polytropic head exponent for this compressor section

The sidestream flow measurement can be compensated for the presence of a valve between the orifice and compressor by desig-nating a Flow Element Pressure Input [MODE:A SS 8]:



Po r,∆ Po d,∆ f2 Rc( )⋅=

Po d,∆ C3 Po ss,∆⋅ C4 Po s,+∆⋅ C5 Po ss,∆ Po s,

+∆⋅+ +=

Po s,+∆

Po ss,∆f2 Rc( )

Po s,+∆

Po s,∆ Po d,∆ f2 Rc( )⋅= f2 X( ) x1 σ–=

Po ss,∆ PV1 PVn Pss⁄( )⋅=

September 2005 IM301 (6.1.3)



If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its sidestream flow (CH1) or fails to receive a valid reported flow for the adjacent compressor section (if serial communication fails or that controller has fallen back to fD 31). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].

If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the flow input is good but the suction pressure input (CH3) is not. The controller then falls back to minimum flow control, using the Default Minimum Flow [COND:A CONST 2] as its set point. Assum-ing this input failed low, its loss would also drive the Reported Flow Characterizer’s argument (Rc) to its highest possible value (10):

Thus, if another controller needs this section’s ∆Po,s, COND:A f(X) 2 9 should be given a worst-case value that can be calculated as:

If ∆Pc Substitution [MODE:A SS 6 1] has been set to LOW, thus enabling calculation of Ps from Pss and ∆Pc, the failure of either pressure input would prevent the calculation of Ps and would there-fore trigger this fallback. If fD 32 is disabled, any condition that would otherwise trigger it will instead trigger the Default Output Fallback.


If fD 33 is disabled, the failure of either pressure input will trigger the Minimum Flow Fallback. Low failure of the discharge pressure would drive the Reported Flow Characterizer’s argument to zero:

Thus, if another controller needs this section’s ∆Po,s, COND:A f(X) 2 0 should be given the same worst-case value as f(X) 2 9:

SsConst 2

Po d,∆ f2 10( )⋅-----------------------------------=

f2 10( ) Po s,∆ Po d,∆⁄( )min=

Ss

K f1 Const 3( ) Ps f3 N( )⋅ ⋅ ⋅Po d,∆ f2 Const 3( )⋅

-----------------------------------------------------------------=

SsConst 2

Po d,∆ f2 0( )⋅--------------------------------=

f2 10( ) Po s,∆ Po d,∆⁄( )min=

September 2005 IM301 (6.1.3)




If the Adjacent Section Flow Fallback [MODE:A fD 3 7] is enabled, the flow measurement will be calculated from a Default Adjacent Section Flow [COND:A CONST 7] if the controller fails to receive a flow measurement for the adjacent compressor section:

However, the resulting flow measurement will be used for control purposes only if fD 31 is disabled.


Ss K f1 Rc( ) Ps f3 Const 5( )⋅ ⋅ ⋅ Po r,∆⁄=


Po d,∆ C3 Po+∆⋅ C4 CONST 7⋅ C5 Po

+∆ CONST 7⋅+ +=

Ss Const 8 f1 Rc( ) f3 N( ) Ps⋅ ⋅ ⋅ Po r,∆⁄=

September 2005 IM301 (6.1.3)


Mode fA 51 Compression Ratio / Reduced Power


where:




J = Drive Power (PV1)






The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced power) as a function of the compression ratio. The General Characterizer [COND:A f(X) 5 # and X 5 #] can then further define the surge limit as a function of a secondary coordinate specified as the f5 Argument [MODE:A SS 9]. Guide vane angle is perhaps the most common secondary coordi-nate, as shown in the accompanying P&ID.

Because reduced power is defined as:

,

Ps

UIC FY

PT

Pd

4 23

N

PT

1

J

SIC

Ss

K f1 Rc( ) f3 N( ) Ps f5 U5( )⋅ ⋅ ⋅ ⋅J

-----------------------------------------------------------------------=

jr J N Ps⋅( )⁄=

September 2005 IM301 (6.1.3)


the X Coordinate Characterizer [COND:A f(X) 3 # and X 3 #] should be proportional to its argument:

To use analog input CH4 as the speed input (as indicated), disable the Rotational Speed Source [MODE:A ANIN 4]. Alternately, you can obtain that variable from a companion Speed or Fuel Controller by setting that parameter equal to its Controller ID Number.

If there are significant power losses, the f5 function can be used to define net power consumption as a function of the drive power input:

In this case, the f5 Argument should be the drive power input (CH1).

If you do not plan to detect surge by monitoring drive power, that signal can be connected to an analog input other than CH1, which should then be specified as the f5 Argument. The General Charac-terizer should then define net power as a function of that input:

The algorithm for Ss will then be equivalent to:

PV1 should then be given a constant value by setting its Process Variable Gain [COND:A GAIN 1] to zero and its Process Variable Bias [BIAS 1] equal to the desired value of PV1. If an appropriate signal is connected to CH1, surge can be detected by monitoring its rate of change (that is, the derivative of SV1, which is not affected by the CH1 Process Variable Gain and Bias).

You can also use PV1 to implement a variable gain that can be manipulated via analog input CH1.

f3 N( ) N∝

f5 J( ) J Jnet⁄=

f5 J( ) Jnet1–

=

Ss

K f1 Rc( ) N Ps Jnet⁄⋅ ⋅ ⋅PV1

--------------------------------------------------------=

September 2005 IM301 (6.1.3)


Fallback Strategies: If fA 51 is selected, the potentially applicable fallbacks are fD 31, 32, 35, 36, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered when the controller detects the failure of its drive power input (CH1). It then holds the actuator control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].

If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the power input is good but either pressure input is not. The controller then falls back to minimum power control, with the Default Minimum Flow [COND:A CONST 2] as its set point:






Ss Const 2 J⁄=

Ss K f1 Rc( ) f3 Const 5( ) Ps f5 U5( )⋅ ⋅ ⋅ ⋅ J⁄=


Ss K f1 Rc( ) f3 N( ) Ps f5 Const 6( )⋅ ⋅ ⋅ ⋅ J⁄=


Ss Const 8 f1 Rc( ) f3 N( ) Ps f5 U5( )⋅ ⋅ ⋅ ⋅ J⁄=

September 2005 IM301 (6.1.3)


Mode fA 61 Compression Ratio / (Reduced Flow = ∆Po/Ps)2, with General Characterizer


where:








The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced flow) as a function of the compression ratio. The General Characterizer [COND:A f(X) 5 # and X 5 #] can then further define the surge limit as a function of a secondary coordinate specified as the f5 Argument [MODE:A SS 9]. Guide vane angle is perhaps the most common secondary coordi-nate, as shown in the accompanying P&ID.

Flow can be measured as the pressure drop across an orifice in either suction or discharge. Suction flow measurements can be compensated for the presence of a valve between the orifice and

FT

UIC FY

ZT

Pd∆Po

3 2?

PT

Ps

PT

1

α


Ss

K f1 Rc( ) Ps f5 U5( )⋅ ⋅ ⋅Po c,∆

-----------------------------------------------------=

September 2005 IM301 (6.1.3)


compressor inlet by designating a Flow Element Pressure Input [MODE:A SS 8]:


If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report a squared mass flow to its companions, the cal-culation of which normally requires an orifice temperature:

where:

β5 = Mass Flow Coefficient [COND:A β 5]

Pc = Compensating Pressure Input [MODE:D fD 2]

Tc = Compensating Temperature Input [MODE:D fD 3]

These compensating inputs are scaled as described on page 58. If the flow is measured in suction, fD 2 should be set to 3 to use Ps as the compensating pressure. If flow is measured in discharge, set fD 2 to 2 to select Pd.

This mode is not usually used for the first or last section of a com-pressor if 34 or 35 is used to protect the other sections (31 or 33 is preferable). However, it can be if fD 2 and fD 3 have the same value, so that W2 is proportional to ∆Po,c.

Fallback Strategies: If fA 61 is selected, the potentially applicable fallbacks are fD 31, 32, 33, 36, and 38.

If enabled, the Default Output Fallback [MODE:A fD 3 1] is triggered whenever the controller detects the failure of its flow input. It then holds the control signal at a constant value specified by the Fallback Minimum Recycle [COND:A CONST 1].




W 2 β5 Po c,∆ Pc Tc⁄⋅ ⋅=


September 2005 IM301 (6.1.3)







Ss K f1 Const 3( ) Ps f5 U5( )⋅ ⋅ ⋅ Po c,∆⁄=

Ss K f1 Rc( ) Ps f5 Const 6( )⋅ ⋅ ⋅ Po c,∆⁄=


Ss Const 8 f1 Rc( ) Ps f5 U5( )⋅ ⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)


Mode fA 63 Compression Ratio / (Reduced Flow in Suction)2, with General Characterizer, for flow measured in discharge


where:

∆Po,d = Calculated Flow Measurement (PV1)







Td = Discharge Temperature (PV5)

Ts = Suction Temperature (PV6)

The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] de-fines the surge limit (minimum reduced flow in suction) as a function of the compression ratio. The General Characterizer [COND:A f(X) 5 # and X 5 #] can then further define the surge limit as a function of a secondary coordinate specified as the f5 Argument [MODE:A SS 9]. Guide vane angle is perhaps the most common secondary coordinate, as shown in the accompanying P&ID.

UIC FY

TdPs

6

α

?3

Ts Pd

51

∆Po,d

2

TT PTPT TTZT FT

Ss

K f1 Rc( ) f5 U5( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po d,∆------------------------------------------------------------------=

September 2005 IM301 (6.1.3)


Reduced flow in suction is represented as:

Because this mode should be used only if flow is measured in dis-charge and the Flow Element Pressure Input [MODE:A SS 8] can only compensate for the presence of a suction control valve, that parameter should be disabled.

If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its squared mass flow to its companions. Because flow is measured in discharge, the Compensating Pres-sure Input and Compensating Temperature Input should also select discharge measurements [MODE:D fD 2 = 2 and fD 3 = 5].

Aftercooler FlowMeasurements

This mode can also be used when the flow is measured down-stream from an aftercooler, provided the pressure drop across that cooler is negligible. In addition to connecting ∆Po,ac to CH1, CH5 should be connected to an aftercooler temperature (Tac) rather than the discharge temperature (Td).





If either temperature input fails and the Sigma Fallback [MODE:A fD 3 4] is enabled, the controller will calculate reduced flow in suction from the Default Sigma [COND:A CONST 4]:

A similar approach is used if only the discharge pressure input fails and both the Compression Ratio Fallback [MODE:A fD 3 3] and

q r s,2 Po s,∆

Ps--------------

W2 Ts Ps⁄⋅Ps

----------------------------- Po d,∆Ts Pd⋅

Ps2 Td⋅

-----------------⋅= = =

Ss Const 2 Po d,∆⁄=

Ss

K f1 Rc( ) f5 U5( ) Ps RcConst 4 1–⋅ ⋅ ⋅ ⋅

Po d,∆---------------------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)


Sigma Fallback [MODE:A fD 3 4] are enabled. Proximity to surge is then calculated from the Default Compression Ratio [COND:A CONST 3] and Default Sigma [COND:A CONST 4]:

If either fD 33 or fD 34 is disabled, a discharge pressure failure will again trigger the Minimum Flow Fallback.




Ss

K f1 Const 3( ) f5 U5( ) Ps Const 3Const 4 1–⋅ ⋅ ⋅ ⋅Po d,∆

---------------------------------------------------------------------------------------------------------------------=

Ss

K f1 Rc( ) f5 Const 6( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po d,∆--------------------------------------------------------------------------------=


Ss

Const 8 f1 Rc( ) f5 U5( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po d,∆------------------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 65 Reduced Head / (Reduced Flow = ∆Po/Ps)2, with General Characterizer


where:


f1(hr) = Y Coordinate Characterizer

f3(0) = first point of X Coordinate Characterizer








The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced flow) as a function of reduced polytropic head. The first point of the X Coordinate Charac-terizer [COND:A f(X) 3 # and X 3 #] is used as a scaling constant that allows the Y Coordinate Characterizer to be more precisely defined when the maximum value of hr is considerably less than ten.

UIC FY

Td

∆Po,s?

Ps

1

α

36

Ts Pd

25

FT ZTTT TTPT PT

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps⋅ ⋅ ⋅Po c,∆

----------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


The General Characterizer [COND:A f(X) 5 # and X 5 #] can then further define the surge limit as a function of a secondary coordinate specified as the f5 Argument [MODE:A SS 9]. Guide vane angle is perhaps the most common secondary coordinate, as shown in the accompanying P&ID.

Flow can be measured as the pressure drop across an orifice in either suction or discharge. Suction flow measurements can be compensated for the presence of a valve between the orifice and compressor inlet by designating a Flow Element Pressure Input [MODE:A SS 8], and connecting an appropriate pressure signal:


If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its squared mass flow to its companions. If the suction flow is measured, the Compensating Pressure Input and Compensating Temperature Input should also select suction mea-surements [MODE:D fD 2 = 3 and fD 3 = 6]. If flow is measured in discharge, those parameters should also select discharge measure-ments [MODE:D fD 2 = 2 and fD 3 = 5].

Constant SigmaImplementation

If you enable the Constant Sigma [MODE:A fC 2] implementation, reduced head is calculated without any temperature measurements:

where:

Const 4 = Default Sigma [COND:A CONST 4]






h r RcConst 4 1–( ) Const 4⁄=


September 2005 IM301 (6.1.3)


If only the discharge and/or suction temperature fails and the Sigma Fallback [MODE:A fD 3 4] is enabled, the controller will calculate reduced head from the Default Sigma [COND:A CONST 4]:

If fD 34 is disabled, the failure of the discharge pressure or either temperature input will trigger the Minimum Flow Fallback.

If both the Compression Ratio Fallback [MODE:A fD 3 3] and Sigma Fallback [MODE:A fD 3 4] are enabled, they are triggered if the dis-charge pressure fails. Reduced head is then calculated from the Default Compression Ratio [COND:A CONST 3] and Default Sigma [COND:A CONST 4]:

If fD 33 is disabled, a discharge pressure failure will trigger the Mini-mum Flow Fallback.





h r Const 3Const 4 1–( ) Const 4⁄=

Ss K f1 hr( ) f3 0( )⋅[ ] Ps f5 Const 6( )⋅ ⋅ ⋅ Po c,∆⁄=


Ss Const 8 f1 hr f3 0( )⋅[ ] Ps f5 U5( )⋅ ⋅ ⋅ Po c,∆⁄=

September 2005 IM301 (6.1.3)


Mode fA 67 Reduced Head / (Reduced Flow in Suction)2, with General Characterizer, for flow measured in discharge


where:

∆Po,d = discharge Calculated Flow Measurement (PV1)










The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced flow) as a function of reduced polytropic head. The first point of the X Coordinate Charac-terizer [COND:A f(X) 3 # and X 3 #] is used as a scaling constant

FT

UIC FY

ZT

Td ∆Po,d

2

TT

Ps

TT

6

α

PT PT

?3

Ts Pd

51

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po d,∆---------------------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


that allows the Y Coordinate Characterizer to be more precisely defined when the maximum value of hr is considerably less than ten.



Because this mode should be used only if flow is measured in dis-charge and the Flow Element Pressure Input [MODE:A SS 8] can only compensate for the presence of a suction control valve, that parameter should be disabled.

If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its squared mass flow to its companions. Because flow is measured in discharge, the Compensating Pres-sure Input and Compensating Temperature Input should also select discharge measurements [MODE:D fD 2 = 2 and fD 3 = 5].



where:


and polytropic compression is assumed, so that:



If enabled, the Minimum Flow Fallback [MODE:A fD 3 2] is triggered when the flow input is good but the suction pressure input (CH3) is

q r s,2 Po s,∆

Ps--------------

W2 Ts Ps⁄⋅Ps

-----------------------------Po d,∆ Pd⋅

Td--------------------------

Ts

Ps2

------⋅= = =

Ss K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps RcConst 4 1–⋅ ⋅ ⋅ ⋅ Po d,∆⁄=


Ps Td⋅Ts Pd⋅-----------------

Td Ts⁄Pd Ps⁄-----------------

Rcσ

Rc------- Rc

σ 1–= = =

September 2005 IM301 (6.1.3)


not. The controller then falls back to minimum flow control, using the Default Minimum Flow [COND:A CONST 2] as its set point:


If only the discharge and/or suction temperature fails and the Sigma Fallback [MODE:A fD 3 4] is enabled, the controller will calculate reduced head from the Default Sigma [COND:A CONST 4]:

If fD 34 is disabled, the failure of either temperature input will trigger the Minimum Flow Fallback.


If either fD 33 or fD 34 is disabled, a discharge pressure failure will trigger the Default Output Fallback.


Ss Const 2 Po d,∆⁄=

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps RcConst 4 1–⋅ ⋅ ⋅ ⋅

Po d,∆------------------------------------------------------------------------------------------------------=

hr RcConst 4 1–( ) Const 4⁄=

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps Const 3Const 4 1–⋅ ⋅ ⋅ ⋅Po d,∆

----------------------------------------------------------------------------------------------------------------------=

hr Const 3Const 4 1–( ) Const 4⁄=

Ss

K f1 hr f3 0( )⋅[ ] f5 Const 6( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po d,∆-----------------------------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)





Ss

Const 8 f1 hr f3 0( )⋅[ ] f5 U5( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po d,∆--------------------------------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 68 Reduced Head / (Reduced Flow in Suction)2, with General Characterizer, for flow measured downstream from aftercooler


where:

∆Po,ac = aftercooler Calculated Flow Measurement (PV1)








Tac = aftercooler discharge temperature (PV7)



The Y Coordinate Characterizer [COND:A f(X) 1 # and X 1 #] defines the surge limit (minimum reduced flow) as a function of

TT

UIC

FY

PT

Td Tac

5

PT

Ps

TT

3

α

ZT TT

2?

Ts Pd

71

FT

6

∆Po,ac

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( )Ps

2 Tac⋅Ts Pd⋅--------------------⋅ ⋅ ⋅

Po ac,∆------------------------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


reduced polytropic head. The first point of the X Coordinate Charac-terizer [COND:A f(X) 3 # and X 3 #] is used as a scaling constant that allows the Y Coordinate Characterizer to be more precisely defined when the maximum value of hr is considerably less than ten.



where the pressure drop across the aftercooler is assumed to be negligible, so that Pac = Pd.

Because this mode should be used only if flow is measured down-stream from an aftercooler and the Flow Element Pressure Input [MODE:A SS 8] can only compensate for the presence of a suction control valve, that parameter should be disabled.

If Series Load Variable [MODE:A fC 9] is disabled, a controller using this mode will report its squared mass flow to its companions. Because the aftercooler pressure drop is assumed to be negligible, the Compensating Pressure Input should select the discharge pres-sure [MODE:D fD 2 = 2]. The Compensating Temperature Input should select the aftercooler temperature [MODE:D fD 3 = 7].



where it is assumed that Tac and Ts are controlled (so that their ratio is a constant) and:



If the aftercooler temperature input fails, the controller will calculate proximity to surge by substituting the discharge temperature:

q r s,2 Po s,∆

Ps--------------

W2 Ts Ps⁄⋅Ps

----------------------------- Po ac,∆Ts Pd⋅

Ps2 Tac⋅

--------------------⋅= = =

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps2 Pd⁄( )⋅ ⋅ ⋅

Po ac,∆--------------------------------------------------------------------------------------=


Ss K f1 hr( ) f3 0( )⋅ f5 U5( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅ Po ac,∆⁄=

September 2005 IM301 (6.1.3)


Because Pd is presumably higher than Pac, this produces a more aggressive but less efficient control action.




If only the discharge temperature input fails and the Sigma Fallback [MODE:A fD 3 4] is enabled, the controller will calculate reduced head from the Default Sigma [COND:A CONST 4]:

A similar approach is taken if only the suction temperature input fails. In that case, however, the controller must also assume the dis-charge temperature equals the presumably lower aftercooler temperature (as it does when Tac fails), so that:

Proximity to surge can thus be calculated as:

Again, this approach produces a more aggressive (though less effi-cient) control action. If fD 34 is disabled, the failure of either Ts or Td will trigger the Minimum Flow Fallback.

Ss Const 2 Po ac,∆⁄=

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( )Ps

2 Tac⋅Ts Pd⋅--------------------⋅ ⋅ ⋅

Po ac,∆------------------------------------------------------------------------------------=


Ps Tac⋅Ts Pd⋅-------------------

Ps Td⋅Ts Pd⋅----------------- Rc

σ 1–=<

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps RcConst 4 1–⋅ ⋅ ⋅ ⋅

Po ac,∆------------------------------------------------------------------------------------------------------=


September 2005 IM301 (6.1.3)



If either fD 33 or fD 34 is disabled, a discharge pressure failure will again trigger the Minimum Flow Fallback.




Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Ps Const 3Const 4 1–⋅ ⋅ ⋅ ⋅Po ac,∆

----------------------------------------------------------------------------------------------------------------------=

hr Const 3Const 4 1–( ) Const 4⁄=

Ss

K f1 hr f3 0( )⋅[ ] f5 Const 6( )Ps

2 Tac⋅Ts Pd⋅--------------------⋅ ⋅ ⋅

Po ac,∆-------------------------------------------------------------------------------------------------=


Ss

Const 8 f1 hr f3 0( )⋅[ ] f5 U5( )Ps

2 Tac⋅Ts Pd⋅--------------------⋅ ⋅ ⋅

Po ac,∆-----------------------------------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)



Appendix FS fA Mode SupplementThis appendix provides basic documentation of application functions that are not recommended for general use:

• Some have been superseded by improved algorithms based on the same coordinate system, while

• Others have proven impractical or ineffective.

Although they have been retained within the control program to sup-port legacy systems, none of these fA modes should be employed unless recommended by our engineering staff.

This manual addendum is included to:

• provide basic documentation of these fA Modes,

• identify recommended alternatives from among the modes described in Appendix F.

September 2005 IM301 (6.1.3)

194 Appendix FS : fA Mode Supplement

Mode fA 32 Compression Ratio / (Reduced Flow2 = ∆Po/Ps),with X Coordinate Characterizer


where:


f1() = Y Coordinate Characterizer

f3() = X Coordinate Characterizer






The X Coordinate Characterizer [COND:A f(X) 3 # and X 3 #] should be defined as a constant rather than to define the surge limit as a function of speed. Proximity-to-surge would then be calculated as:

If we compare this defining equation to those for fA 33 (see page 161) and 61 (see page 176), we see that they are identical except that fA 32 does not include the General Characterizer. If we com-pare it to fA 31 (see page 158), we see that they are identical.

Thus, if f5 is not needed, this mode could be used to calculate prox-imity to surge as described for fA 33, but it would be easier to use fA 31 (which does not require you to set the eighteen parameters that define f3). If f5 is needed, fA 33 can be used to calculate Ss in the same fashion as fA 61.

Conversely, if f5 is defined as a constant, a controller using fA 61 or fA 33 will calculate the same proximity to surge as one using fA 32.

Ss

K f1 Rc( ) Ps f3 N( )[ ]⋅ ⋅ ⋅Po c,∆

-------------------------------------------------------=

Ss

K f1 Rc( ) Ps⋅ ⋅Po c,∆

---------------------------------∝

Note:The speed input of a revision 754-001 or later Antisurge Controller can be monitored and recorded even if the selected fA Mode does not require that input.

September 2005 IM301 (6.1.3)


Mode fA 36 Reduced Head / (Reduced Flow2 = ∆Po/Ps)


where:


hr = Reduced Head







σ = Polytropic Head Exponent

This mode assumes that the ratio of reduced head to reduced flow at the surge limit is a constant. This will be generally be true only in low compression ratio applications or when the speed, suction tem-perature, and gas composition are all constant. In such cases, the added complexity of and additional inputs required by this mode usually provide no improvement in surge protection compared to modes based on the (compression ratio, reduced flow) coordinate system. Thus, this fA Mode has been and should be rarely used.

In applications for which this mode would be appropriate, fA 65 (see page 182) will calculate the same proximity-to-surge if the Y Coordi-nate Characterizer [COND:A f(X) 1 # and X 1 #] is defined as an identity [f1(hr) = hr], the General Characterizer [COND:A f(X) 5 # and X 5 #] is defined as a constant, and the first point of the X Coor-dinate Characterizer [COND:A f(X) 3 # and X 3 #] is defined as unity [f(X) 3 0 = 1.00]. Equally-good protection can usually be obtained using fA 61 (see page 176).

Ss

K hr Ps⋅ ⋅Po c,∆

-----------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 37 Reduced Head / (Reduced Flow in Suction)2,for flow measured in discharge


where:


hr = Reduced Head








This mode assumes that the ratio of reduced head to reduced flow at the surge limit is a constant. This will be generally be true only in low compression ratio applications or when the speed, suction tem-perature, and gas composition are all constant. In such cases, the added complexity of and additional inputs required by this mode usually provide little if any improvement in surge protection com-pared to modes based on the (compression ratio, reduced flow) coordinate system. Thus, this fA Mode has been and should be rarely used.

In applications for which this mode would be appropriate, fA 67 (see page 185) will calculate the same proximity-to-surge if the Y Coordi-nate Characterizer [COND:A f(X) 1 # and X 1 #] is defined as an identity [f1(hr) = hr], the General Characterizer [COND:A f(X) 5 # and X 5 #] is defined as a constant, and the first point of the X Coor-dinate Characterizer [COND:A f(X) 3 # and X 3 #] is defined as unity [f(X) 3 0 = 1.00].

However, because the (reduced flow, reduced head) coordinate system remains invariant even if reduced flow is calculated as ∆Po,d/Ps or ∆Po,d/Pd, it would be equally valid and simpler to use fA 65. Equally-good protection can usually be obtained using fA 61 (see page 176).

Ss

K hr

Ps2 Td⋅

Ts Pd⋅-----------------⋅ ⋅

Po c,∆-----------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 38 Reduced Head / (Reduced Flow in Suction)2, for flow measured downstream from aftercooler


where:


hr = Reduced Head





Tac = aftercooler temperature (PV7)




This mode assumes that the ratio of reduced head to reduced flow at the surge limit is a constant. This will be generally be true only in low compression ratio applications or when the speed, suction tem-perature, and gas composition are all constant. Thus, this fA Mode has been and should be rarely used.

In applications for which this mode would be appropriate, fA 68 (see page 189) will calculate the same proximity-to-surge if the Y Coordi-nate Characterizer [COND:A f(X) 1 # and X 1 #] is defined as an identity [f1(hr) = hr], the General Characterizer [COND:A f(X) 5 # and X 5 #] is defined as a constant, and the first point of the X Coor-dinate Characterizer [COND:A f(X) 3 # and X 3 #] is defined as unity [f(X) 3 0 = 1.00].

Ss

K hr

Ps2 Tac⋅

Ts Pd⋅--------------------⋅ ⋅

Po c,∆--------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 39 Reduced Head / (Reduced Flow2 = ∆Po/Ps),with X Coordinate Characterizer


where:



hr = Reduced Head










Because this is identical to the defining equation for 36 (see page 195), one of that mode’s preferred alternates should always be used in situations to which fA 39 might otherwise seem applicable.

Ss

K hr Ps f3 N( )[ ]⋅ ⋅ ⋅Po c,∆

---------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

Ss

K hr Ps⋅ ⋅Po c,∆

-----------------------=

September 2005 IM301 (6.1.3)


Mode fA 40 Reduced Head / (Reduced Flow in Suction)2,with X Coordinate Characterizer, for flow measured in discharge


where:



hr = Reduced Head











Ss

K hr

Ps2 Td⋅

Ts Pd⋅----------------- f3 N( )[ ]⋅ ⋅ ⋅

Po c,∆----------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

Ss

K hr

Ps2 Td⋅

Ts Pd⋅-----------------⋅ ⋅

Po c,∆-----------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 41 Reduced Head / (Reduced Flow in Suction)2, with X Coordinate Characterizer, for flow measured downstream from aftercooler


where:



hr = Reduced Head












Ss

K hr

Ps2 Tac⋅

Ts Pd⋅-------------------- f3 N( )[ ]⋅ ⋅ ⋅

Po c,∆------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

Ss

K hr

Ps2 Tac⋅

Ts Pd⋅--------------------⋅ ⋅

Po c,∆--------------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 42 Reduced Head / (Reduced Flow in Suction)2, with X Coordinate and General Characterizers


where:





hr = Reduced Head









The X Coordinate Characterizer [COND:A f(X) 3 # and X 3 #] should be defined as a constant rather than to define the surge limit as a function of speed. The above defining equation would then be the same as that for fA 65 (see page 182), but fA 65 only requires you to set one of the eighteen parameters needed to define the f3 charac-terizer as a constant.

Ss

K f1 hr f3 N( )( )⋅[ ] f5 U5( ) Ps⋅ ⋅ ⋅Po c,∆

---------------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 43 Reduced Head / (Reduced Flow in Suction)2, with X Coordinate and General Characterizers, for flow measured in discharge


where:





hr = Reduced Head










However, because the (reduced head, reduced flow) coordinate system remains invariant even if reduced flow is calculated as ∆Po,d/Ps or ∆Po,d/Pd, it would be equally valid and simpler to use fA 65.

Ss

K f1 hr f3 N( )( )⋅[ ] f5 U5( )Ps

2 Td⋅Ts Pd⋅-----------------⋅ ⋅ ⋅

Po c,∆---------------------------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 44 Reduced Head / (Reduced Flow in Suction)2, with X Coordinate and General Characterizers, flow measured downstream of aftercooler


where:





hr = Reduced Head











Ss

K f1 hr f3 N( )( )⋅[ ] f5 U5( )Ps

2 Tac⋅Ts Pd⋅--------------------⋅ ⋅ ⋅

Po c,∆------------------------------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 46 Compression Ratio / (Equivalent Speed)2


where:









It is not invariant to changes in gas composition and is usually insuf-ficiently sensitive to provide effective antisurge control.

Ss

K f1 Rc( ) f3 N( ) Ts⋅ ⋅ ⋅PV1

--------------------------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 47 Reduced ∆Tc-Based Head / (Equivalent Speed)2


where:


f5(Ts) = General Characterizer





Rc = Compression Ratio (Pd /Ps)

Rt = Temperature Ratio (Td /Ts)

∆Tc = temperature rise across compressor

Td = Discharge Temperature (∆Tc + Ts)


∆V = voltage differential between transposed Td and Ts thermocouples (PV5)


It is not invariant to changes in gas composition and is usually insuf-ficiently sensitive to provide effective antisurge control.

Ss

K Tc∆ σ⁄[ ] f3 N( )⋅ ⋅PV1

------------------------------------------------= Tc∆ V∆ f5 Ts( )⋅= σRtlog

Rclog----------------=

September 2005 IM301 (6.1.3)


Mode fA 48 Reduced ∆Tc-Based Head / (Equivalent Speed)2, with General Characterizer, for constant σ


where:


f5(Ts) = General Characterizer



∆Tc = temperature rise across compressor


∆V = voltage differential between transposed Td and Ts thermocouples (PV5)

It is not invariant to changes in gas composition, does not allow for characterization of the surge limit, and is usually insufficiently sensi-tive to provide effective antisurge control.

S s

K Tc∆ f 3 N( )⋅ ⋅PV1

------------------------------------= Tc∆ V∆ f5 Ts( )⋅=

September 2005 IM301 (6.1.3)


Mode fA 50 Reduced Head / (Equivalent Speed)2, with General Characterizer


where:








Rt = Temperature Ratio (Td /Ts)




It is not invariant to changes in gas composition, does not allow for characterization of the surge limit, and is usually insufficiently sensi-tive to provide effective antisurge control.

Ss

K h r f 3 N( ) Ts f5 U5( )⋅ ⋅ ⋅ ⋅PV1

--------------------------------------------------------------= hr

Rcσ 1–

σ----------------= σ

Rtlog

Rclog----------------=

September 2005 IM301 (6.1.3)


Mode fA 62 Compression Ratio / (Reduced Flow = ∆Po/Pd)2, with General Characterizer


where:








Except for using Pd (rather than Ps) to calculate reduced flow, this is identical to the defining equation for fA 61 (see page 176), which should be used if flow is measured in suction. Applications using a discharge flow measurement can use either fA 61 or 63 (see page 179).

Ss

K f1 Rc( ) Pd f5 U5( )⋅ ⋅ ⋅Po c,∆

------------------------------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 64 Compression Ratio / (Reduced Flow · Equiv. Speed)2, with General Characterizer


where:






Pd = Discharge Pressure (PV2) of this section

Pss = Suction Pressure (PV3) of this section


W = mass flow through this section

This mode was developed for compressor sections with no flow measurement, but proved impractical to tune. Such applications should use either fA 34 (see page 165) or 35 (see page 169).

Ss

K f1 Rc( ) f3 N( ) Pss2 f5 U5( )⋅ ⋅ ⋅ ⋅

W2--------------------------------------------------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 66 Reduced Head / (Reduced Flow = ∆Po/Pd)2, with General Characterizer


where:











Except for using Pd (rather than Ps) to calculate reduced flow, this is identical to the defining equation for fA 65 (see page 182), which should be used if flow is measured in suction. Applications using a discharge flow measurement can use either fA 65 or 67 (see page 185). Those measuring flow downstream from an aftercooler should use fA 68 (see page 189).

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( ) Pd⋅ ⋅ ⋅Po c,∆

----------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


Mode fA 69 Reduced Head / (Reduced Flow in Discharge)2, with General Characterizer, for flow measured downstream from aftercooler


where:

∆Po,ac = aftercooler Calculated Flow Measurement (PV1)








Tac = aftercooler discharge temperature (PV7)



Except for correcting the flow measurement to discharge rather than suction conditions, this is identical to the defining equation for fA 68 (see page 189), which is usually a more practical solution for such aftercooler applications.

Ss

K f1 hr f3 0( )⋅[ ] f5 U5( )Pd Tac⋅

Td--------------------⋅ ⋅ ⋅

Po ac,∆------------------------------------------------------------------------------------=

hr

Rcσ 1–

σ----------------= σ

Td Ts⁄( )log

Pd Ps⁄( )log-------------------------------=

September 2005 IM301 (6.1.3)


September 2005 IM301 (6.1.3)



Glossary/IndexThis combined glossary and index defines and references various topics discussed in this manual.

AccumulatedIntegral Response

is the sum of the integral, loop-decoupling, and primary capacity control response changes, adjusted to keep the Intended Valve Position between its Output Clamps.

Reference: Antisurge Control Response. . . . . . . . . . . . . . . . . 77Output Clamps . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Actuator ControlSignal

is the intended value of the analog signal used to manipulate the Anti-surge Valve. It is calculated by applying the Valve Dead Band Compensation, Output Clamp, Tight Shut-Off Response, and Output Reverse features to the Intended Valve Position, and is displayed by the front-panel Output Readout (OUT).

Reference: Actuator Control Signal. . . . . . . . . . . . . . . . . . . . . 99Analog Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Adjacent SectionFlow

is the Reported Flow received from the Antisurge Controller for the adja-cent section of a multisection compressor.

Reference: Equivalent Flow Measurements . . . . . . . . . . . . . . 85

Adjacent SectionFlow Fallback

substitutes a default value if a valid Reported Flow is not received from that section’s controller.

Reference: Adjacent Section Flow Fallback . . . . . . . . . . . . . . 70

AftercoolerCompensation

adjusts a flow measured downstream from an aftercooler to suction or discharge conditions.

Reference: Aftercooler Flow Measurement. . . . . . . . . . . . . . . 57

see also: Calculated Flow Measurement

Alternate K see: Valve-Sharing Fallback

AlternateParameter Sets

are three sets of configuration and tuning parameters that the controller can store in addition to its primary (working) set. If enabled, discrete input D7 loads either the first or second alternate set. Recalling an alternate set causes a Controller Reset.

Reference: Alternate Parameter Sets . . . . . . . . . . . . . . . . . . 106Checksums. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142Storing and Recalling . . . . . . . . . . . . . . . . . . . . . 141

Alternate Readout is a front-panel Readout (ALT) that displays the Surge Count or a Pres-sure Limiting threshold when the corresponding key is pressed.

see: page 2 of DS301/O

September 2005 IM301 (6.1.3)

214 Index

Analog Input is a circuit that measures the signal from a process variable transmitter, or the value of such a signal. Series 3 Plus Controllers have eight such inputs that are referred to as channels 1 through 8 (CH1 through CH8).

Reference: Analog Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Application Function Table. . . . . . . . . . . . . . . . . .151Disabling Input Signals. . . . . . . . . . . . . . . . . . . . . .37Signal Values Test . . . . . . . . . . . . . . . . . . . . . . . .144

see also: Analog-to-Digital Variable, Measured Variable, Process Variable, Signal Variable, Transmitter Testing

Analog Output is a circuit that generates a continuously-variable signal usually used to manipulate a control element, or the value of such a signal.

Reference: Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

see also: Actuator Control Signal, Output Loopback Test

Analog PCB is a printed circuit board that provides a Series 3 Plus Controller’s Analog Inputs and Analog Outputs.

Reference: Analog Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

see also: Analog PCB Assembly section in Chapter 1 of IM300/H

Analog-to-DigitalVariable

is an internal, percent-of-maximum representation of an Analog Input signal.

Reference: Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

Antisurge Control is the manipulation of an Antisurge Valve to prevent surge while minimiz-ing recycling or blowoff.

Reference: Continuous Operation . . . . . . . . . . . . . . . . . . . . . .27Major Features . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Antisurge ControlResponse

is the intended recycle or blowoff flow rate, which is calculated by adding Loop Decoupling and Primary Capacity Control responses to selected proportional, integral, and Recycle Trip responses

Reference: Antisurge Control Response . . . . . . . . . . . . . . . . .77

see also: Antisurge PI Response, PI and RT Signal Selection, Pressure Limiting, Recycle Trip Response

AntisurgeDeviation

is a control variable representing the distance between the operating point and the Surge Control Line. It is the complement of the Proximity to Surge variable calculated by the Application Function.

Reference: Continuous Operation . . . . . . . . . . . . . . . . . . . . . .27Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . .72

Antisurge PIResponse

is a proportional-integral response to the deviation of the operating point from the Surge Control Line.

Reference: Antisurge PI Response . . . . . . . . . . . . . . . . . . . . .79PI and RT Signal Selection . . . . . . . . . . . . . . . . . .77Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . .72

see also: PI Algorithm, PI and RT Signal Selection

September 2005 IM301 (6.1.3)


Antisurge Valve is a control valve that can be opened to increase the total flow through a compressor by recycling or blowing-off some of that flow.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 26Output Clamps . . . . . . . . . . . . . . . . . . . . . . . . . . 100Output Reverse. . . . . . . . . . . . . . . . . . . . . . . . . . 101Output Tracking . . . . . . . . . . . . . . . . . . . . . . . . . 102Remote Low Output Clamp . . . . . . . . . . . . . . . . 100Tight Shut Off Response . . . . . . . . . . . . . . . . . . 101Valve Dead Band Compensation . . . . . . . . . . . . . 99Valve Flow Characterization . . . . . . . . . . . . . . . . . 98Valve Position Test . . . . . . . . . . . . . . . . . . . . . . . . 43

see also: Actuator Control Signal

ApplicationFunction

is the method used to calculate Proximity to Surge.

Reference: Proximity to Surge . . . . . . . . . . . . . . . . . . . . . . . . 63

AutomaticOperation

is a mode of operation in which the Intended Recycle Flow is calculated by the automatic control responses.

Reference: Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 26Sequencing Operation . . . . . . . . . . . . . . . . . . . . . 30

AutomaticSequence

is a series of actions that start, stop, load, or unload a compressor.

Reference: Operating States. . . . . . . . . . . . . . . . . . . . . . . . . 103Sequencing Operation . . . . . . . . . . . . . . . . . . . . . 30

see also: Emergency Shutdown, Normal Shutdown, Operating State, Startup

Auxiliary LimitingControl

is the use of a Performance Controller to implement limiting control of a variable other than the suction and discharge pressure.

Reference: Auxiliary Limiting. . . . . . . . . . . . . . . . . . . . . . . . . . 83PI and RT Signal Selection. . . . . . . . . . . . . . . . . . 77

Auxiliary Readout is a twelve-character front-panel Readout (AUX) that displays various internal and process variables.

Reference: Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 26Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . 32Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . . . . 29Surge Protection . . . . . . . . . . . . . . . . . . . . . . . . . . 26

see also: page 2 of DS301/O

Baud Rates see: Serial Port

Beep Frequency is the frequency of the beep sound, which can be varied by pressing the Raise or Lower Key while holding down the Scroll Key.


September 2005 IM301 (6.1.3)

216 Index

Blow-Off Valve is a control valve used to release compressed air to the atmosphere in order to raise a compressor’s gross flow rate above its surge limit.

see: Antisurge Valve

Brighter Displays see: Display Brightness

BumplessTransfer

is a transition between automatic and manual operation or surge protec-tion and pressure limiting that is achieved without a sudden antisurge valve movement.

Reference: Antisurge PI Response . . . . . . . . . . . . . . . . . . . . .79Output Tracking . . . . . . . . . . . . . . . . . . . . . . . . . .102Restoring Automatic. . . . . . . . . . . . . . . . . . . . . . . .33

Calculated FlowMeasurement

is a measurement of the total flow through the compressor, which can be calculated from a single analog input or as a function of several inputs and signals obtained from other controllers.

Reference: Calculated Flow Measurement. . . . . . . . . . . . . . . .54Characterizing Functions . . . . . . . . . . . . . . . . . . . .64Equivalent Flow Measurements . . . . . . . . . . . . . . .85

see also: Aftercooler Compensation, Control Valve Compensation, Discharge Flow Measurement, Multisection Compressors

CalculatedVariables

are computed or specially-scaled variables representing process condi-tions. Most are calculated only if required by the Application Function, and some can be displayed by the Auxiliary Readout.

Reference: Calculated Variable Displays . . . . . . . . . . . . . . . . .60

CentralProcessing Unit

is the computer chip that executes the Control Program.

see: CPU PCB Assembly section in Chapter 1 of IM300/H

CharacterizingFunctions

are user-defined functions used to calculate Proximity to Surge and the control line margins.

Reference: Configuring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

Check Valve allows flow in only one direction. One is generally used to prevent reverse flow into the compressor from the discharge header.

Checksum see: Cyclic Redundancy Checksum

Coil Bit is a Modbus bit that a host can write to in order to change some aspect of the controller’s operation (similar to a discrete input).

see: Series 3 Plus Antisurge Controller Modbus Data Sheet [DS301/M]

Cold-RecycleControl

is the use of an Antisurge or Performance Controller to regulate the flow of process gas through a recycle heat exchanger common to several compressors operating in parallel. An Antisurge Controller is configured for this application by selecting Application Function 00.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Cold-Recycle Control . . . . . . . . . . . . . . . . . . . . . . .95fA 00. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152

September 2005 IM301 (6.1.3)


COMMAND is our Compressor Monitoring and Display software for IBM-PC compati-ble Operator Workstations.

CommunicationErrors

see: Serial Port

CompensatingPressure

see: Mass Flow Rates

CompensatingTemperature

see: Mass Flow Rates

CompressionRatio

is the ratio of discharge to suction pressure.

Reference: Calculated Variable Displays . . . . . . . . . . . . . . . . 60Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

CompressionRatio Fallback

calculates proximity to surge from a default compression ratio if the dis-charge pressure input fails.

Reference: Compression Ratio Fallback. . . . . . . . . . . . . . . . . 69

Compressor Map is a graphical depiction of compressor performance, usually a plot of head as a function of flow.

CompressorSurge

is a potentially damaging reversal of flow that occurs under high com-pression, low flow conditions.

Computer Control is the monitoring and control of a Series 3 Plus Controller via serial com-munication from a host device using the Modbus protocol.

Reference: Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 26Modbus Configuration. . . . . . . . . . . . . . . . . . . . . . 50Operator Interfaces. . . . . . . . . . . . . . . . . . . . . . . . 25Serial Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

see also: Series 3 Plus Antisurge Controller Modbus Data Sheet [DS301/M]

Computer IDNumber

is a number between 1 and 64 that identifies a Series 3 Plus Controller on its Serial Port 2, 3, and 4 communication networks.

Reference: ID Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Redundant Tracking . . . . . . . . . . . . . . . . . . . . . . 106

Computer Inhibit is the limitation of a Modbus host’s ability to read or change a Series 3 Plus Controller’s registers and coils.

Reference: Modbus Configuration. . . . . . . . . . . . . . . . . . . . . . 50

ComputerWorkstation

see: Operator Workstation

Configuration is the adaptation of a controller to a specific application by setting its Con-figuration Parameters.

Reference: Enabling and Disabling . . . . . . . . . . . . . . . . . . . . 143

see also: Chapter 3 of IM300/H

September 2005 IM301 (6.1.3)

218 Index

ConfigurationParameters

are a set of numeric and other values that enable, disable, or otherwise control the features of the controller.

see: Alternate Parameter Sets

Configurator see: Toolbox

Constant Sigma see: Polytropic Head Exponent

Control Element see: Antisurge Valve

Control Key is one of the eight push-buttons molded into the Front Panel that alter various aspects of the controller’s operation when pressed.

Reference: Signal Values Test . . . . . . . . . . . . . . . . . . . . . . . .145


Control Line is a line on a compressor map indicating the area in which a specific con-trol action is taken.

Reference: Control Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

see also: Recycle Trip Line, Safety On Line, Surge Control Line, Tight Shut-Off Line

Control Program is the Signal Variable that defines the controller’s features and control actions, which is stored in its EEPROM and can be downloaded from an Operator Workstation.

see: Download, Program Checksum, Program Version

Control Relay see: Discrete Output

Control Response see: Antisurge Control Response

Control Signal see: Actuator Control Signal

Control Valve see: Antisurge Valve

Control ValveCompensation

is a flow measurement adjustment that compensates for a pressure drop across a valve between the flow-measuring element and compressor.

Reference: Control Valve Compensation . . . . . . . . . . . . . . . . .56Fallback Strategies. . . . . . . . . . . . . . . . . . . . . . . . .67

see also: Calculated Flow Measurement

Control Variable see: Antisurge Deviation, Proximity to Surge, Pressure Limiting

Control VariableFilters

are software filters that can be applied to the calculated Proximity to Surge and Polytropic Head Exponent.

Reference: Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Head. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

Controller Fault see: Fault

Controller IDNumber

is a number between 1 and 8 that identifies a Series 3 Plus Controller on a Serial Port 1 communication network.

Reference: ID Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Redundant Tracking. . . . . . . . . . . . . . . . . . . . . . .106

September 2005 IM301 (6.1.3)


Controller Reset is a restart of the Control Program, which occurs when the controller is powered up or certain faults occur. It can also be initiated by recalling Alternate Parameter Sets, reconfiguring the controller from an Operator Workstation, or entering the Reset Controller [MODE COMM] key sequence.

Reference: CPU Reset Count . . . . . . . . . . . . . . . . . . . . . . . . 146Reset Controller . . . . . . . . . . . . . . . . . . . . . . . . . 140

CPU PCB is a circuit board that provides the controller’s Central Processing Unit, Discrete Inputs, Discrete Outputs, and Serial Ports.

see: CPU PCB Assembly section in Chapter 1 of IM300/H

CyclicRedundancy

Checksum

is a four-digit hexadecimal number calculated by applying a standard mathematical function to a group of numbers.

see: Parameter Checksum, Program Checksum

Dead Zone see: Derivative Response, Deviation Dead Zone

Default OutputFallback

holds the output constant when inputs required by the selected Applica-tion Function and any less drastic fallbacks fail.

Reference: Default Output Fallback . . . . . . . . . . . . . . . . . . . . 67

Default AdjacentSection Flow

see: Adjacent Section Flow Fallback

DefaultCompression

Ratio

see: Compression Ratio Fallback

Default f5Argument

see: Function 5 Fallback

Default MinimumFlow

see: Minimum Flow Fallback

Default Sigma see: Sigma Fallback, Startup

Default Speed see: Speed Fallback

Default VaneAngle

see: Function 5 Fallback

DerivativeResponse

is a feature that increases the Surge Control Margin as a function of the rate at which the operating point is approaching its surge limit.

Reference: Derivative Response. . . . . . . . . . . . . . . . . . . . . . . 74Maximum Derivative . . . . . . . . . . . . . . . . . . . . . . 147Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . 72

Deviation see: Antisurge Deviation, Pressure Limiting

Deviation DeadZone

is a region about the Surge Control Line in which the deviation from that line is considered to be zero.

September 2005 IM301 (6.1.3)

220 Index

DEViationReadout

is a front-panel Readout (DEV) that shows the Antisurge Deviation.

Reference: Surge Protection . . . . . . . . . . . . . . . . . . . . . . . . . .27


Dimmer Displays see: Display Brightness

Disabling Inputs can be accomplished by enabling the input lockout parameter, so that the analog and discrete input signals can be controlled via serial communica-tion when testing or demonstrating the controller.

Reference: Disabling Input Signals. . . . . . . . . . . . . . . . . . . . . .37

Discharge FlowMeasurement

is a flow that is measured downstream from the compressor. The Series 3 Plus Antisurge Controller can calculate Proximity to Surge directly from such a measurement or adjust it to suction conditions.

see: Calculated Flow Measurement

DischargePressure

see: Pressure Limiting, Pressure Measurements

DischargeTemperature

see: Temperature Measurements

Discrete Bit is a Modbus bit that a host can read to monitor some aspect of the con-troller’s operation (functionally similar to a discrete output).


Discrete Input is a signal from another device that can have one of two values, or a cir-cuit that reads such a signal. The functions of the Antisurge Controller’s inputs are listed and cross-referenced in Table 3-3.

Reference: Disabling Input Signals. . . . . . . . . . . . . . . . . . . . . .37Discrete Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Signal Values Test . . . . . . . . . . . . . . . . . . . . . . . .145

Discrete Output is a relay that can be included in an external circuit and energizes or de-energizes to indicate the state of an internal variable or condition that can have one of two values. Each of the Antisurge Controller’s outputs can be independently assigned any of the functions listed and cross-referenced in Table 3-4.

Reference: Discrete Outputs . . . . . . . . . . . . . . . . . . . . . . . . . .45Signal Values Test . . . . . . . . . . . . . . . . . . . . . . . .145

DisplayBrightness

is the brightness of the front-panel Readouts, which can be toggled between their bright and dim levels by simultaneously pressing the Raise and Display Limit keys.


Displayed MassFlow

is the Flow calculated variable, which can be net or total mass flow.

Reference: Displayed Mass Flow . . . . . . . . . . . . . . . . . . . . . . .61

Download is our Control Program updating Software for IBM-PC compatible Opera-tor Workstations.

September 2005 IM301 (6.1.3)


Drive Power see: Reduced Power

EmergencyShutdown

is an Automatic Sequence that immediately opens the Antisurge Valve.

Reference: Sequencing Operation . . . . . . . . . . . . . . . . . . . . . 30Shutdown Configuration . . . . . . . . . . . . . . . . . . . 104

see also: Normal Shutdown

Engineering Panel is a keyboard and alphanumeric readout located behind the Front Panel from which Configuration and Test Procedures can be run.

Reference: Keyboard Configuration . . . . . . . . . . . . . . . . . . . 107Serial Communication Errors . . . . . . . . . . . . . . . . 49

see also: Front Panel Assembly section in Chapter 1 of IM300/H

Equivalent FlowMeasurement


Equivalent Speed is an invariant coordinate variable that is a function of speed, tempera-ture, and gas composition.

Reference: Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

External Alarms are lights, horns, and other devices connected to Discrete Outputs and set up to indicate undesirable controller or process conditions.

Reference: External Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . 45

fA Mode see: Application Function

Fails-Closed is a method of specifying Valve Direction by the position it takes if its control signal fails (falls to zero). Because some valves fail in place, spec-ifying the direction its moves when that signal increases (Signal-to-Close or Signal-to-Open) is preferred.

see: Output Reverse

Fallback Strategy is a method used to provide continued control or protection when an oth-erwise required input signal fails.

Reference: Calculated Variable Displays . . . . . . . . . . . . . . . . 60Fallback Strategies . . . . . . . . . . . . . . . . . . . . . . . . 67Fault Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

see also: Adjacent Section Flow Fallback, Compression Ratio Fallback, Default Output Fallback, Function 5 Fallback, Minimum Flow Fallback, Polytropic Head Fallback, Sigma Fallback, Speed Fallback, Valve-Sharing Fallback

Fault is an internal malfunction that prevents the controller from functioning as intended, which is indicated by the Fault LED or Fault Relays.

Reference: Fault Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Fault Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Switching Conditions . . . . . . . . . . . . . . . . . . . . . 106

see also: Chapter 8 of IM300/H

Fails-Open

September 2005 IM301 (6.1.3)

222 Index

Field Input/OutputModule

is a Field Termination Assembly that provides all of the I/O terminals for a compressor controller.

Reference: Hardware Options . . . . . . . . . . . . . . . . . . . . . . . . .37

Field TerminationAssembly

is an external module that provides terminals for I/O signal wires.

see: Field Termination Assemblies section in Chapter 1 of IM300/H

Filters see: Control Variable Filters

Flow Limits see: Output Clamp

FlowMeasurements

are analog input signals that are proportional to the square of the com-pressor’s total or sidestream flow.


Front Panel provides the controller’s primary operator interface (Control Keys, Read-outs, and LED Indicators).

Reference: Front Panel Reset Count . . . . . . . . . . . . . . . . . . .146Operator Interfaces . . . . . . . . . . . . . . . . . . . . . . . .25

see also: Series 3 Plus Antisurge Controller Operator Interface Description [DS301/O]

Fuel Controller is a Series 3 Plus Controller that can be combined with Antisurge and Performance Controllers to provide Total Train Control for a gas-turbine-driven compressor.

Reference: Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

Function 5Fallback

substitutes a default value if the input designated as the argument for the General Characterizer (f5) fails.

Reference: Function 5 Fallback . . . . . . . . . . . . . . . . . . . . . . . .70

Gas CompositionCompensation

see: Surge Limit Characterization

General PIAlgorithm

see: PI Algorithm

Guide Vanes direct the flow of gas toward a compressor rotor. If their angle can be var-ied relative to the approaching flow, they can be used to manipulate the compressor’s performance (throughput). Surge Limit Characterization must then be used to calculate an invariant Proximity to Surge.

HardwareConfiguration

is one of four possible combinations of internal PCBs and Back Panels, two of which are suitable to Antisurge Controllers.


see also: Components and Configurations section in Chapter 1 of IM300/H

High-DensityInterconnect

Cable

connects a Field Input/Output Module to the controller.


September 2005 IM301 (6.1.3)


Holding Register is a Modbus number a host can write to in order to change some aspect of the controller’s operation (similar to an analog input).


Hysteresis is a directional variation of a control response that is often confused with but is not the same as a dead zone.

see: Dead Zone, Valve Dead Band Compensation

ID Numbers are numbers that identify the controller to other devices on a serial com-munications network.

Reference: ID Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

InitialComputation

see: Application Function

Input Register is a Modbus number a host can read in order to monitor some aspect of the controller’s operation (similar to an analog output).


Intended RecycleFlow

see: Antisurge Control Response

Intended ValvePosition

is the intended position of the Antisurge Valve (in percent open), which is calculated by applying Valve Flow Characterization to the intended recy-cle flow rate (Antisurge Control Response).

Reference: Intended Valve Position . . . . . . . . . . . . . . . . . . . . 98

see also: Actuator Control Signal

InvariantCoordinate

System

is a set of compressor performance measurements that yields the same Proximity to Surge value under all possible conditions.

LED Indicator is one of the fourteen solid-state lamps mounted in the lower left portion of the Front Panel that light to indicate various conditions.


Limiting Control see: Auxiliary Limiting Control, Pressure Limiting, Performance Override

Load Balancing distributes the total load on a group of compressors by configuring their Performance Controllers to equalize an appropriate variable calculated by the Antisurge Controllers.

Reference: Characterizing Functions . . . . . . . . . . . . . . . . . . . 64Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Load Sharing is a division of the required total load or capacity among two or more compressors.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 29Networked Compressors . . . . . . . . . . . . . . . . . . . 92

see also: Cold-Recycle Control, Load Balancing, Performance Override, Primary Capacity Control, Recycle Balancing

September 2005 IM301 (6.1.3)

224 Index

Load Variable is the load-balancing variable (L) calculated by the Antisurge Controllers in a series load-sharing application.

Reference: Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . .93

Load-SharingController

is a Performance Controller that is used to regulate the capacity of one of several compressors operating in parallel or in series.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . .93Port 2 Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . .94

Loop Decoupling is the adjustment of the control responses of the various controllers regu-lating a given process to minimize adverse interactions.

Reference: Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . .83PI and RT Signal Selection . . . . . . . . . . . . . . . . . .77

Manual Operation is a mode in which the Intended Recycle Flow is varied by the raise and lower keys or computer control interface.

Reference: Manual Operation. . . . . . . . . . . . . . . . . . . . . . . . . .32Shutdown Configuration. . . . . . . . . . . . . . . . . . . .104

Manual Override is a group of features that can limit the circumstances under which man-ual operation can be initiated or might be automatically suspended or terminated.

Reference: Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Manual Operation. . . . . . . . . . . . . . . . . . . . . . . . . .33

Margin of Safety see: Surge Control Margin

Mass Flow Rates are flow rates calculated from flow, temperature, and pressure measurements.

Reference: Mass Flow Rates . . . . . . . . . . . . . . . . . . . . . . . . . .58

see also: Displayed Mass Flow, Load Balancing, Net Mass Flow

MeasuredVariable

is a scaled representation of an Analog Input signal that can be displayed via the Auxiliary Readout’s Analog In Menu.

Reference: Measured Variables . . . . . . . . . . . . . . . . . . . . . . . .40

Minimum FlowFallback

is the maintenance of a minimum flow rate when an input required to compute the Application Function’s head coordinate fails and no less drastic fallback is appropriate or available.

Reference: Minimum Flow Fallback . . . . . . . . . . . . . . . . . . . . .68

Modbus Communication channel and protocol used for Computer Control.

see: Modbus Reference [IM300/M]

Modbus RegisterScaling

is applied to Modbus register values reported via Serial Port 3, which can range from zero to either 100 or 102.4 percent.

Reference: Modbus Configuration . . . . . . . . . . . . . . . . . . . . . .50

September 2005 IM301 (6.1.3)


MultisectionCompressors

are multiple rotor compressors that have intercoolers or sidestreams between their suction and discharge ports.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Multisection Compressors . . . . . . . . . . . . . . . . . . 85

Net Mass Flow is a mass flow rate calculated by subtracting the estimated recycle flow from the total flow.

Reference: Displayed Net Mass Flow . . . . . . . . . . . . . . . . . . . 62

No-Flow Modes are Application Functions for compressors that have no flow measuring element.

Reference: fA 51 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Non-Linear ValveCharacterization

see: Valve Flow Characterization

Normal Shutdown is an Automatic Sequence that ramps open the Antisurge Valve.

Reference: Sequencing Operation . . . . . . . . . . . . . . . . . . . . . 30Shutdown Configuration . . . . . . . . . . . . . . . . . . . 104

see also: Emergency Shutdown

Normally-Closed refers to the position of a relay’s contacts when it is de-energized. This nomenclature applies even if the coil is usually energized, in which case the normally-closed contacts would usually be open and the normally-open contacts would usually be closed!

Offset Zero Input is a transmitter signal that has a minimum value that is typically 20 per-cent of the maximum value (for example, a 4 to 20 mA signal).

see: Signal Variable

Operating State is a basic mode of operation in which the control valve is modulated to prevent surge (Run State), held open (Shutdown State), held closed (Purge State), or held in a position dictated by another controller (Track-ing State).

Reference: Operating States. . . . . . . . . . . . . . . . . . . . . . . . . 103

Operating StateRequest Signals

are discrete, analog, and serial input signals that can be used to select an Operating State, thus triggering an Automatic Sequence.

Reference: Operating States. . . . . . . . . . . . . . . . . . . . . . . . . 103

Operator Interface is provided primarily by the Front Panel, although some functions can be implemented by Remote Control or Computer Control.

Reference: Modbus Configuration. . . . . . . . . . . . . . . . . . . . . . 50Operator Interfaces. . . . . . . . . . . . . . . . . . . . . . . . 25

see also: Series 3 Plus Antisurge Controller Operator Interface Description [DS301/O]

Normally-Open

September 2005 IM301 (6.1.3)

226 Index

OperatorWorkstation

is an IBM-PC compatible computer running controller monitoring or sup-port software (such as COMMAND or Toolbox). Reconfiguring a controller from a workstation causes a Controller Reset.

Reference: Serial Ports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

Output Clamp is a limitation placed on the Actuator Control Signal.

Reference: Manual Operation. . . . . . . . . . . . . . . . . . . . . . . . . .32Output Clamps . . . . . . . . . . . . . . . . . . . . . . . . . . .100

see also: Remote Low Output Clamp

Output LoopbackTest

is a comparison of the analog Actuator Control Signal, as measured by analog input CH8, to its intended value.

Reference: Fault Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . .35Output Loopback Test . . . . . . . . . . . . . . . . . . . . . .42

Output Readout is a front-panel Readout (OUT) that displays the Actuator Control Signal.


Output Reverse adapts the Actuator Control Signal to the Valve Direction.

Reference: Output Reverse . . . . . . . . . . . . . . . . . . . . . . . . . .101

Output Tracking is a feature that keeps the Actuator Control Signal equal to a designated analog input.

Reference: Output Tracking . . . . . . . . . . . . . . . . . . . . . . . . . .102Tracking States . . . . . . . . . . . . . . . . . . . . . . . . . . .36

see also: Remote Low Output Clamp

ParameterChecksum

is a Cyclic Redundancy Checksum calculated for the controller’s Configu-ration Parameters.

Reference: Parameter Checksum . . . . . . . . . . . . . . . . . . . . .142

Parity Settings see: Serial Port

PerformanceController

is a Series 3 Plus Controller that regulates a dynamic compressor’s throughput (capacity), usually by manipulating its throttling element to maintain a desired flow rate or pressure.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15Auxiliary Limiting . . . . . . . . . . . . . . . . . . . . . . . . . .83Cold-Recycle Control . . . . . . . . . . . . . . . . . . . . . . .95Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . .83Networked Compressors . . . . . . . . . . . . . . . . . . . .92Operating States . . . . . . . . . . . . . . . . . . . . . . . . .103Performance Override . . . . . . . . . . . . . . . . . . . 29, 83Serial Ports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

see also: Performance Controller [IM302]

PerformanceCurve

is a curve on a Compressor Map plotting the head, power, or discharge pressure at various flow rates.

September 2005 IM301 (6.1.3)


PerformanceOverride

is a cooperative feature that can raise the compressor’s recycle rate if a companion Performance Controller’s performance override variable exceeds its control threshold.

Reference: Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29PI and RT Signal Selection. . . . . . . . . . . . . . . . . . 77

PI Algorithm is an implementation of the Proportional-Integral method of calculating a control response from the deviation between a control variable and its set point.

Reference: General PI Algorithm . . . . . . . . . . . . . . . . . . . . . . 78

see also: Antisurge PI Response, PI and RT Signal Selection

PI and RT SignalSelection

keeps the recycle or blowoff rate high enough to satisfy several control objectives by selecting the highest of the proportional, integral, and Recy-cle Trip control responses from the corresponding loops and controllers.

Reference: PI and RT Signal Selection. . . . . . . . . . . . . . . . . . 77

Polytropic Head see: Reduced Head

Polytropic HeadExponent

is a variable used in calculating reduced polytropic head, designated by the Greek letter sigma and often referred to as such.

Reference: Calculated Variable Displays . . . . . . . . . . . . . . . . 60Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Startup Configuration . . . . . . . . . . . . . . . . . . . . . 104


calculates polytropic head from temperature measurements and a default exponent if the discharge pressure measurement fails.

Position Failure see: Valve Position Test

Power Algorithm is an Application Function based on head and power consumption.

Reference: fA 51 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Pressure Limiting raises the recycle rate as needed to limit the minimum suction or maxi-mum discharge pressure.

Reference: Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 29Fallback Strategies . . . . . . . . . . . . . . . . . . . . . . . . 67Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . 32PI and RT Signal Selection. . . . . . . . . . . . . . . . . . 77Pressure Limiting . . . . . . . . . . . . . . . . . . . . . . . . . 82

see also: Auxiliary Limiting Control, Performance Override

PressureMeasurements

are usually scaled directly from assigned analog inputs, although either the discharge or suction pressure can be calculated from the other and the pressure rise across the compressor.

Reference: Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

September 2005 IM301 (6.1.3)

228 Index

Pressure Rise is the difference between the suction and discharge pressures. The Series 3 Plus Antisurge Controller can calculate either of those measure-ments from the other and their difference.

Reference: Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51


is the regulation of the throughput of a group of compressors by basing the control actions of each compressor’s Performance and Antisurge Controllers on that of a Station Controller.

Reference: PI and RT Signal Selection . . . . . . . . . . . . . . . . . .77Primary Capacity Control . . . . . . . . . . . . . . . . . . . .92

Process Variable is a process condition measured by an assigned Analog Input.

Reference: Application Function. . . . . . . . . . . . . . . . . . . . . . . .63Process Variables . . . . . . . . . . . . . . . . . . . . . . . . .40

see also: Measured Variable, Signal Variable

ProgramChecksum

is a Cyclic Redundancy Checksum calculated from the controller’s Con-trol Program.

Reference: Program Checksum . . . . . . . . . . . . . . . . . . . . . . .146

Program Version is the revision level of the software installed in a Series 3 Plus Controller (for example, 756-004).

Reference: Program Version . . . . . . . . . . . . . . . . . . . . . . . . .144

Proportional-Integral Response

see: Antisurge PI Response, PI Algorithm, PI and RT Signal Selection

Proximity to Surge is a variable that indicates how close the compressor is to surging. Ide-ally, its value should always be one when the compressor is operating at its surge limit (on the verge of surging).

Reference: Proximity to Surge . . . . . . . . . . . . . . . . . . . . . . . . .63

see also: Antisurge Deviation, Application Function

Purge State is an Operating State that holds the recycle valve closed so purge gas can be forced through the compressor.

Reference: Operating States . . . . . . . . . . . . . . . . . . . . . . . . .103Sequencing Operation . . . . . . . . . . . . . . . . . . . . . .31

Readout is one of four displays (Alternate Readout, Auxiliary Readout, DEViation Readout, and Output Readout) in the upper portion of the Front Panel.


Recycle Balancing is the deliberate equalization of the recycle rates of compressors operat-ing in parallel.

Reference: Recycle Balancing . . . . . . . . . . . . . . . . . . . . . . . . .94

Recycle Trip Line is a Control Line representing the minimum distance from the Surge Con-trol Line below which the Recycle Trip Response will open the Antisurge Valve.

September 2005 IM301 (6.1.3)


Recycle TripMargin

is the distance between the Recycle Trip and Surge Limit Lines.

Recycle TripResponse

is an open-loop control response that ratchets open the Antisurge Valve when the compressor gets too close to its surge limit.

Reference: Continuous Operation. . . . . . . . . . . . . . . . . . . . . . 27Force Recycle Trip Test . . . . . . . . . . . . . . . . . . . 143Maximum Derivative . . . . . . . . . . . . . . . . . . . . . . 147PI and RT Signal Selection. . . . . . . . . . . . . . . . . . 77Recycle Trip Line . . . . . . . . . . . . . . . . . . . . . . . . . 73Recycle Trip Response. . . . . . . . . . . . . . . . . . . . . 80

Recycle Valve is a control valve used to return compressed gas to the compressor intake in order to raise the total flow rate above its surge limit.

see: Antisurge Valve

Reduced Flow is an invariant coordinate variable calculated by dividing a flow measure-ment by a pressure.

Reference: Reduced Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Reduced Head is an invariant coordinate variable representing the head developed by the compressor, calculated from the compression and temperature ratios.

Reference: Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Reduced Power is an invariant coordinate variable calculated from power, speed, and pressure measurements.

Reference: Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

RedundantController

is a Series 3 Plus Controller installed so that it serves as an on-line backup to another.

Reference: Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 106Tracking States. . . . . . . . . . . . . . . . . . . . . . . . . . . 36

see also: Redundant Controllers section in Chapter 8 of IM300/H

Remote Control is the use of analog and discrete inputs and outputs to monitor and manipulate the controller and compressor.

Reference: Analog Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Discrete Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Discrete Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . 45Operator Interfaces. . . . . . . . . . . . . . . . . . . . . . . . 25


is a variable Actuator Control Signal limit that is set via a designated ana-log input.

Reference: Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . 32Remote Low Output Clamp . . . . . . . . . . . . . . . . 100

see also: Output Tracking

Remote OperatorPanel

is a group of push buttons, indicators, and analog displays used for Remote Control of the compressor and its controllers.

September 2005 IM301 (6.1.3)

230 Index

Reported Flow is an Equivalent Flow Measurement or mass flow rate reported to com-panion controllers.

Reference: Reported Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

ResettingController

see: Controller Reset

Resistance Curve is a curve on a Compressor Map plotting the head, power, or discharge pressure needed to achieve various flow rates.

Rotational Speed can be measured by an analog input or obtained from a Speed, Fuel, or Performance Controller. A properly-selected Application Function will be invariant to speed changes.

Reference: Displayed Speed . . . . . . . . . . . . . . . . . . . . . . . . . .61Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

see also: Speed Fallback, Surge Limit Characterization

Run State is an Operating State that varies the recycle rate of a running compressor as needed to efficiently prevent surge.

Reference: Continuous Operation . . . . . . . . . . . . . . . . . . . . . .26Operating States . . . . . . . . . . . . . . . . . . . . . . . . .103

Safety Margin is the distance between the operating point and Surge Limit Line.

Safety On Line is a Control Line representing the distance from the Surge Limit Line at which the Safety On Response will assume a surge has occurred and increase the Surge Control Margin.

Safety On Margin is the distance between the Safety On and Surge Limit Lines.

Safety OnResponse

increases the Surge Control Margin if operating conditions indicate a surge has occurred.

Reference: Continuous Operation . . . . . . . . . . . . . . . . . . . . . .27Maximum Flow Derivatives . . . . . . . . . . . . . . . . .148Maximum Pressure Derivatives . . . . . . . . . . . . . .149Recycle Trip Line . . . . . . . . . . . . . . . . . . . . . . . . . .73Safety On Line . . . . . . . . . . . . . . . . . . . . . . . . . . . .73Safety On Response . . . . . . . . . . . . . . . . . . . . . . .75Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . .72

Serial Port is a circuit used to exchange data with other electronic devices.

Reference: Fault Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . .34ID Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Serial Communication Errors . . . . . . . . . . . . . . . . .49Serial Communication Formats . . . . . . . . . . . . . . .49Serial Port 1 Test . . . . . . . . . . . . . . . . . . . . . . . . .140Serial Port 2 Test . . . . . . . . . . . . . . . . . . . . . . . . .140Serial Port Activity Text . . . . . . . . . . . . . . . . . . . .144Serial Ports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

see also: Computer Control, Operator Workstation, Redundant Controller

September 2005 IM301 (6.1.3)


ShutdownSequences

see: Emergency Shutdown, Normal Shutdown

Shutdown State see: Stop State

Sidestreams are flows entering or leaving a multisection compressor at a point between two impellers.

see: Multisection Compressors

Sigma see: Polytropic Head Exponent

Sigma Fallback substitutes a default polytropic head exponent if any input required to cal-culate that variable fails.

Reference: Sigma Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Signal Variable is an internal variable representing the percent-of-range value of an Ana-log Input signal.

Reference: Signal Values Test . . . . . . . . . . . . . . . . . . . . . . . 144Signal Variables . . . . . . . . . . . . . . . . . . . . . . . . . . 39

see also: Measured Variable, Process Variable

Signal-to-Close is a method of specifying Valve Direction as the direction it moves as its control signal increases.

see: Output Reverse

Software is a set of instructions that define the functionality of a computerized device (such as an electronic controller) that are usually stored in a device that allows them to be easily updated.

see: Control Program, Program Checksum, Program Version

Sound see: Beep Frequency

Speed see: Rotational Speed, Surge Limit Characterization

Speed Controller is a Series 3 Plus Controller that can be combined with Antisurge and Performance Controllers to provide Total Train Control for a steam-tur-bine-driven compressor.

Reference: Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

see also: Speed Controller [IM307]

Speed Fallback substitutes a default speed if the Rotational Speed source fails.

Reference: Speed Fallback . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Startup is a series of actions, sequenced primarily by the Performance Controller, that starts or loads a compressor.

Reference: Sequencing Operation . . . . . . . . . . . . . . . . . . . . . 31Startup Configuration . . . . . . . . . . . . . . . . . . . . . 104

Signal-to-Open

September 2005 IM301 (6.1.3)

232 Index

Station Controller is a Series 3 Plus Performance Controller configured as a Load Sharing master.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17Cold-Recycle Control . . . . . . . . . . . . . . . . . . . . . . .95Port 2 Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . .94Primary Capacity Control . . . . . . . . . . . . . . . . . . . .92

see also: Chapter 7 of IM302

Status Variable see: Operating State

Stop State is an Operating State that holds the Antisurge Valve open while the com-pressor is shut down.

Reference: Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . .104Operating States . . . . . . . . . . . . . . . . . . . . . . . . .103Sequencing Operation . . . . . . . . . . . . . . . . . . . . . .31

Suction Pressure see: Pressure Limiting, Pressure Measurements

SuctionTemperature

see: Temperature Measurements

Surge see: Compressor Surge

Surge ControlLine

is a Control Line representing the set point for the Antisurge PI Response.

Reference: Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . .72

see also: Deviation Dead Zone

Surge ControlMargin

is the distance between the surge control and surge limit lines.

Surge ControlZone

is an area on the compressor map that lies to the right of the surge con-trol line.

Surge Count is the number of surges detected since the Safety On Response was last reset.

Reference: Surge Detection . . . . . . . . . . . . . . . . . . . . . . . . . . .75

Surge LimitCharacterization

is a method used to reduce the number of coordinates needed to calcu-lated Proximity to Surge, especially when one of the otherwise required coordinate variables cannot be measured or calculated.

Reference: Fixed-Geometry Compressors . . . . . . . . . . . . . . . .65Variable-Geometry Compressors. . . . . . . . . . . . . .66

Surge Limit Line is a line on compressor map representing the minimum flow below which the compressor will surge.

Reference: Surge Control Line . . . . . . . . . . . . . . . . . . . . . . . . .72

see also: Proximity to Surge

Surge Protection is the manipulation of an Antisurge Valve to prevent surge while minimiz-ing recycling or blowoff.

see: Application Function, Antisurge Control Response

September 2005 IM301 (6.1.3)


TemperatureMeasurements

are usually scaled directly from assigned analog inputs, although either the discharge or suction temperature can be calculated from the other and the temperature rise across the compressor.

Reference: Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

TemperatureRatio

is the ratio of the discharge and suction temperatures.

Reference: Calculated Variable Displays . . . . . . . . . . . . . . . . 60Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Temperature Rise is the difference between the suction and discharge temperatures. The Series 3 Plus Antisurge Controller can calculate either of those measure-ments from the other and their difference.

Reference: Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Temperature-Based Head

Fallback

see: Polytropic Head Fallback

Test Procedures are controller and process tests that can be executed from the Engineer-ing Panel.

Throttling Element is a device (speed controller, throttle valve, or guide vanes) used to regu-late the compressor’s throughput.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Tight Shut-OffLine

is a Control Line representing the minimum deviation for the Tight Shut-Off Response.

Tight Shut-OffMargin

is the distance between the tight shut-off and Surge Control Lines.

Tight Shut-OffResponse

fully closes the Antisurge Valve if the control response is at its low clamp and the operating point is to the right of the tight shut-off line.

Reference: Tight Shut-Off Line . . . . . . . . . . . . . . . . . . . . . . . . 74Tight Shut-Off Response . . . . . . . . . . . . . . . . . . 101

Tone see: Beep Frequency

Toolbox is a Series 3 Plus Controller configuration and testing program that can be run on an IBM-PC compatible Operator Workstation. Using it to recon-figure a controller causes a soft Controller Reset.

Tracking State is an Operating State in which a Redundant Controller tracks the opera-tion of its active companion or the Output Tracking feature monitors and duplicates the output signal of another device.

Reference: Tracking States. . . . . . . . . . . . . . . . . . . . . . . . . . . 36

TransmitterTesting

is a comparison of each Analog-to-Digital Variable to its user-specified high and low limits.

Reference: Fault Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Transmitter Status Test . . . . . . . . . . . . . . . . . . . 139Transmitter Testing. . . . . . . . . . . . . . . . . . . . . . . . 39

September 2005 IM301 (6.1.3)

234 Index


adjusts the Intended Valve Position to counter the effects of worn valve linkages.

Reference: Valve Dead Band Compensation . . . . . . . . . . . . . .99

Valve Direction is the relationship between the position of a control valve and the value of its control signal.

see: Output Reverse

Valve FlowCharacterization

adapts the Actuator Control Signal to a quick-opening, or equal-proportion, or linear Antisurge Valve.

Reference: Valve Flow Characterization . . . . . . . . . . . . . . . . .98

Valve PositionTest

compares a valve position measurement (analog input CH7) to the Intended Valve Position.

Reference: Fault Indicators. . . . . . . . . . . . . . . . . . . . . . . . . . . .35Valve Position Test . . . . . . . . . . . . . . . . . . . . . . . .43

Valve Sharing is the protection of a two or more compressor sections by Antisurge Con-trollers that cooperatively modulate a single Antisurge Valve.

Reference: Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Continuous Operation . . . . . . . . . . . . . . . . . . . . . .26Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . .83PI and RT Signal Selection . . . . . . . . . . . . . . . . . .77Valve Sharing. . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Valve Sharing Shutdowns . . . . . . . . . . . . . . . . . .104

Valve-SharingFallback

substitutes an alternate value for the surge limit line slope coefficient if communication with a valve-sharing controller fails.

Reference: Valve-Sharing Fallback . . . . . . . . . . . . . . . . . . . . .70

Valve TravelLimits

see: Output Clamp

Vane Angle see: Guide Vanes

Variable GasComposition

requires that you either select an Application Function that is invariant to that variable or use worst-case tuning.

see: Invariant Coordinate System, Surge Limit Characterization

Watchdog TimeOut

is a feature that forces a Controller Reset if a power interruption or certain internal errors are detected.

see: Fault Indicators section in Chapter 8 of IM300/H

Workstation see: Operator Workstation

September 2005 IM301 (6.1.3)

UDS301/D. Series 3 Plus Antisurge Controller OPC Data Sheet

This data sheet lists and describes the default data items that the Series 3 Plus OPC Server provides for this controller. Cross-references in the following descriptions are to the Antisurge Controller [IM301] instruction manual.

Read-Only Data Items

Read-Write Data Items

Clients can access this data by connecting to the TrainTools.S3p_OPC.1 server and prepend-ing the item names with the COM port number, a colon, the controller’s Computer ID, and a period (for example, COM1:5.CH1).


OPC Data SheetOPC Server Revision: 2.6.8.2

Variable Name Native Type Variable Name Native Type Variable Name Native Type

ANO2 Float FX1_# Float Rc Float

Automatic Boolean FX3_# Float Received_Flow Float

Bias# Float FY1_# Float Recycle_Trip Boolean

b1 Float FY3_# Float Reported_Flow Float

b2 Float Gain# Float Reset Boolean

CH# Float High_Clamp Boolean Rev Float

CH#_fail Short K_W Float Run Boolean

CH#_scaled Float Limit Boolean Safety_On Boolean

COMM_Status Long Low_Clamp Boolean Sigma Float

CRC Short Manual_Override Boolean Speed Float

DEV Float Port1Fail Boolean Ss_Den Float

Displayed_OUT Float Port2Fail Boolean Ss_Num Float

DI# Boolean PV# Float Surge_Count Short

DO# Boolean PV#hi Float Tc Float

Fallback Boolean PV#lo Float Total_b Float

fA_mode Float PV#max Float Tracking Boolean

f_arg Float PV#min Float Tran_Fail Boolean

Flow Float PV#pos Float Version String

Variable Name Native Type Variable Name Native Type Variable Name Native Type

AutomaticW Boolean Manual_OverrideW Boolean Safety_OnW Boolean

b1W Float Manual_TargetW Float SP2W Float

SP3W Float

October 2004 Page 1 of 4 DS301/D (1.1.1)

Data Item Descriptions

ANO2: Intended value of analog OUT2, in percent. See: Analog Outputs in Chapter 3.

Automatic and AutomaticW: On when the controller is operating automatically and Off during manual operation. Setting AutomaticW forces the controller into automatic, clearing it forces the controller into manual. See: Manual Operation in Chapter 2.

Bias#: Process Variable Bias [COND:D BIAS #] configuration parameter (read-only) used to calculate PV#. See: Process Variables in Chapter 3.

b1 : Initial Surge Control Bias [SPEC:A b 1] configuration parameter (read-only). See: Surge Control Line in Chapter 6.

b1W: Initial Surge Control Bias [SPEC:A b 1] configuration parameter (read-write). See: Surge Control Line in Chapter 6.

b2 : Safety On Incremental Bias [SPEC:A b 2] configuration parameter (read-only). See: Surge Control Line in Chapter 6.

CH#: Percent-of-span value of the corresponding analog input signal variable (each 4 to 20 mA input signal is compensated for a twenty percent offset). See: Signal Variables in Chapter 3.

CH#_fail: 1 if corresponding raw analog input signal is below its low alarm threshold, 2 if it is above its high alarm threshold, otherwise 0. Tran_Fail is set if any of these variables have non-zero values. See: Transmitter Testing in Chapter 3.

CH#_scaled: Value of the corresponding measured variable, calculated by scaling analog input CH# between PV#lo and PV#hi. See: Measured Variables in Chapter 3.

COMM_Status: 0 unless the n most recent Modbus requests timed out, in which case it will be 1. The minimum number of requests that must time out (n) is set by the server’s “Timeouts Before COMM Failure” preference (1 by default).

CRC: 16-bit checksum for the controller’s present set of configuration and tuning parameters. See: Parameter Checksum in Appendix B.

DEV: Deviation of the compressor operating point from the surge control line. See: Surge Control Line in Chapter 6.

Displayed_OUT: Percent-open value displayed by the OUT readout. It will be either the same as or the complement of the Manual_TargetW, depending on the Rev setting. See: Actuator Control Signal in Chapter 8.

DI#: On when the corresponding discrete input (1≤#≤7) is asserted, Off when it is cleared. See: Discrete Inputs in Chapter 3.

DO#: On when the corresponding control relay (1≤#≤5) is supposed to be energized, Off when it is supposed to be cleared. Bits corresponding to fault relays reflect only the assigned func-tions and cannot indicate hardware faults. See: Discrete Outputs in Chapter 3.

Fallback: On when any fallback strategy is being used, usually because a required analog or serial input has failed. See: Fallback Strategies in Chapter 5.

fA_mode: Application Function [MODE:A fA] configuration parameter (read-only). See: Application Function in Chapter 5.

f_arg: Same as fY3_0, which some fA modes use instead of evaluating that characterizer. See: Appendix F.


FX1_# and FY1_#: X and Y values of the corresponding data point for the Y Coordinate Char-acterizer. See: Characterizing Functions in Chapter 5.

FX3_# and FY3_#: X and Y values of the corresponding data point for the X Coordinate Char-acterizer. See: Characterizing Functions in Chapter 5.

Flow: Displayed mass flow, prior to inserting decimal point. See: Displayed Flow in Chapter 4.

Gain#: Process Variable Gain [COND:D GAIN #] configuration parameter (read-only) used to calculate PV#. See: Process Variables in Chapter 3.

High_Clamp: Off unless the actuator control signal is at or beyond the maximum recycle or blow-off flow limit. See: Output Clamps in Chapter 8.

K_W: Surge Limit Line Coefficient [SPEC:A K] configuration parameter (read-only). See: Application Function in Chapter 5.

Limit: On when the recycle or blow-off flow is being increased to restore CV2 or CV3 to an acceptable level. See: Pressure Limiting in Chapter 6.

Low_Clamp: Off unless the actuator control signal is at or beyond the minimum recycle or blow-off flow limit. See: Output Clamps in Chapter 8.

Manual_Override and Manual_OverrideW: Manual Override [MODE:A MOR] parameter value. Setting Manual_OverrideW to On disables automatic surge protection when the recycle valve is being manually positioned. See: Manual Override in Chapter 2.

Manual_TargetW: Actuator control signal (ACS, in percent), which is usually the intended value of analog OUT1. If Automatic is cleared, you can control the ACS via this data item. See: Actuator Control Signal in Chapter 8.

Port1Fail: On if the controller fails to receive Port 1 data it has been configured to expect. See: Serial Communication Errors in Chapter 3.

Port2Fail: On if the controller fails to detect expected load-sharing communications on the Port 2 network. See: Serial Communication Errors in Chapter 3.

PV#: Value of the corresponding analog input process variable calculated by applying Gain# and Bias# to CH#. See: Process Variables in Chapter 3.

PV#hi and PV#lo: Scaling range for corresponding CH#_scaled, calculated by applying PV#pos to PV#max and PV#min. See: Measured Variables in Chapter 3.

PV#max: Measured Variable Maximum [COND:D DISPLAY 0 # HIGH] configuration parameter (read-only) for CH#_scaled. See: Measured Variables in Chapter 3.

PV#min: Measured Variable Minimum [COND:D DISPLAY 0 # LOW] configuration parameter (read-only) for CH#_scaled. See: Measured Variables in Chapter 3.

PV#pos: Measured Variable Decimal [COND:D DISPLAY 0 # •] configuration parameter (read-only) for CH#_scaled, presented as 0001 with a decimal in the specified position (for exam-ple, 0.01 if parameter value is 2). See: Measured Variables in Chapter 3.

Rc : Ratio of the discharge and suction pressures. See: Compression Ratio in Chapter 4.

Received_Flow: Reported flow of the Adjacent Section Controller [MODE:A SS 5]. See: Reported Flow in Chapter 7.

Recycle_Trip: On when the compressor operating point is to the left of the Recycle Trip control line. See: Recycle Trip Line in Chapter 6.


Reported_Flow: Flow measurement (∆Po,r / 2 or W2/ 2) or series load balancing parameter (L) this controller is sending to its companions. See: Reported Flow in Chapter 7.

Reset: Set for thirty seconds when the controller is reset, after which it automatically reverts to Off. See: CPU Reset Count in Appendix B.

Rev: Recycle Valve Direction [MODE:A REV] configuration parameter (read-only). See: Output Reverse in Chapter 8.

Run: Set when a startup is initiated and cleared when the compressor is shut down, provided the Stop Requests [MODE:A fB 1] are not disabled. See: Operating State in Chapter 9.

Safety_On and Safety_OnW: On when the cumulative surge count is not zero, thus indicating the Safety On response has increased the margin of safety, and is cleared when that count is reset. Safety_OnW can only be cleared, which resets the surge count and response to zero. See: Surge Counters in Chapter 6.

Sigma: Polytropic head exponent, provided the chosen fA Mode calculates that variable. See: Polytropic Head Exponent in Chapter 4.

Speed: Normalized rotational speed, in percent. See: Speed in Chapter 4.

SP2W: Maximum Discharge Pressure [COND:A SP 2] configuration parameter (read-write). Limit is set if CH2 is above this limit. See: Pressure Limiting in Chapter 6.

SP3W: Minimum Suction Pressure [COND:A SP 3] configuration parameter (read-write). Limit is set if CH3 is below this limit. See: Pressure Limiting in Chapter 6.

Ss_Den and Ss_Num: Denominator (e.g., ∆Po,s /2) and numerator (e.g., K • Ps • hr / 2) of the selected fA mode, which jointly indicate how closely the compressor is operating to its surge limit. If the controller is properly tuned, the compressor will not surge unless the numerator exceeds the denominator (that is, when Ss > 1). See: Application Function in Chapter 5.

Surge_Count: Number of surges detected since the cumulative surge count was last cleared. See: Surge Counters in Chapter 6.

Tc : Temperature Ratio calculated variable. See: Temperature Ratio in Chapter 4.

Total_b: Total margin of safety between the surge limit and surge control lines, obtained by summing the Initial Surge Control Bias, the derivative response, and the accumulated Safety On response. See: Surge Control Line in Chapter 6.

Tracking: On only when this controller is operating as an on-line backup to another (not affected by the output tracking feature). See: Redundant Control in Chapter 2.

Tran_Fail: On when any analog input signal falls outside of its transmitter testing limits (in which case the corresponding CH#_fail will have a non-zero value), Off when all such signals are within their acceptable ranges. See: Transmitter Testing in Chapter 3.

Version: Revision of installed control program. See: Program Version in Appendix B.


Printed in U.S.A.

COMPRESSOR CONTROLS CORPORATION

4725 121st Street, Des Moines, IA 50323, USAL Phone: (515) 270-0857 • Fax: (515) 270-1331 • Web: www.cccglobal.com

U

DS301/MSeries 3 Plus Antisurge Controller Modbus Data Sheet

Coil Bits

Discrete Inputs

Input Registers

Holding Registers

Series 3 Plus

Antisurge Controller Modbus Data Sheet

Product Revision: 756-002

Address Coil Address Coil Address Coil

00001-10 Undefined

(1)

00012 Manual Override 00014 0

00011 Automatic 00013 Safety On 00015-18 1000

(2)

Address Discrete Address Discrete Address Discrete

10001 Automatic 10008 Reset 10017-20 DI Condition 4-7

10002 Manual Override 10009 Tracking 10021 Run

10003 Safety On 10010 Limit 10022 POC Active

10004 Low Clamp 10011-13 DI Condition 1-3 10023 0

10005 High Clamp 10014 Port 1 Fail 10024 0

10006 Recycle Trip 10015 Port 2 Fail 10025-29 DO State 1-5

10007 Tran Fail 10016 Fallback

Address Register Range Address Register Range

30001-08 Channel # 0 to 102.4% 30016 Surge Count integer

30009 Received Flow 0 to 102.4% 30017 Param CRC integer

30010 DEViation -1.00 to 1.048 30018 Pressure Ratio 0 to 64

30011 S

s

Denominator 0 to 102.4% 30019 Temperature Ratio 0 to 64

30012 S

s

Numerator 0 to 102.4% 30020 Speed 0 to 102.4%

30013 Displayed OUT 0 to 102.4% 30021 Analog Output 2 0 to 102.4%

30014 Total b 0 to 102.4% 30022 Flow 0 to 102400

30015 Sigma 0 to 0.999 30023 Reported Flow 0 to 102.4%

Address Register Range Address Register Range

40001 SLL Coefficient 0 to 102.4% 40004 P

d

Limit 0 to 102.4%

40002 Initial b 0 to 102.4% 40005 P

s

Limit 0 to 102.4%

40003 Actuator CS 0 to 102.4% 40006-28 Input Registers

(3)

see above

October 2004 Page 1 of 4 DS301/M (6.1.1)

This data sheet lists this controller’s Modbus coils, discrete bits, and registers. The Series 3 Plus Modbus implementation, including descriptions of data types, register scaling, and available functions, is described in Chapter 2 of IM300/M. Cross-references in the following descriptions are to the Antisurge Controller [IM301] instruction manual.

Note 1: An attempt to read coils 00001 through 00010 will return zeroes.

Note 2: Although they have coil addresses, bits 00015 through 00018 jointly constitute a read-only, four-bit integer identifying the controller type.

Note 3: Each input register can also be read (but not changed) at an address calculated by add-ing its offset (its address minus 30001) to the address of the first undefined holding register.

Coil and Input Bit Descriptions

Automatic: This coil and discrete will be set when the controller is operating automatically and cleared when manual is selected. Setting this coil forces the controller into automatic, clear-ing it forces the controller into manual. See: Manual Operation in Chapter 2.

DI Condition: These discretes reflect the discrete input states. The offsets of the first three bits are 10 greater than the input number (discrete 10011 is for D1), those for D4 to D7 are 13 greater (discrete 10017 is for D4). See: Discrete Inputs in Chapter 3.

DO State: These discretes indicate the intended states of the control relays — each is set when the corresponding output is energized. The offset of each such bit is 24 greater than the out-put number (discrete 10025 is for CR1 and discrete 10029 is for CR5). Bits corresponding to fault relays reflect only the assigned functions and cannot indicate hardware faults. See: Discrete Outputs in Chapter 3.

Fallback: This discrete is set when any fallback strategy is being used, usually because a required analog or serial input has failed. See: Fallback Strategies in Chapter 5.

High Clamp: Either this or the Low Clamp discrete is set whenever the actuator control signal is at one of its range limits. The High Clamp corresponds to the maximum and the Low Clamp corresponds to the minimum recycle or blow-off. See: Output Clamps in Chapter 8.

Limit: This discrete is set when the recycle or blow-off flow is being increased to restore CV2 or CV3 to an acceptable level. See: Pressure Limiting in Chapter 6.

Low Clamp: see High Clamp

Manual Override: This coil and discrete are set when the Manual Override [MODE:A MOR] parameter is On and cleared when it is Off. Setting this coil enables that parameter, clearing it disables it. Automatic surge protection is active during manual control only if these bits are cleared! See: Manual Override in Chapter 2.

POC Active: This discrete is set when the recycle flow rate has been elevated to help restore a Performance Controller’s performance override control variable to an acceptable value. See: Performance Override in Chapter 6.

Port 1 Fail: This discrete is set when the controller fails to receive Port 1 data it has been config-ured to expect. See: Serial Communication Errors in Chapter 3.

Port 2 Fail: This discrete is set if the controller fails to detect expected communications on the Port 2 load-sharing network. See: Serial Communication Errors in Chapter 3.

Recycle Trip: This discrete is set whenever the operating point is to the left of the Recycle Trip control line. See: Recycle Trip Line in Chapter 6.


Reset: This discrete is set whenever the controller is reset and is cleared thirty seconds later. See: CPU Reset Count in Appendix B.

Run: Provided the Stop Requests [MODE:A fB 1] is not disabled, this discrete is set when a startup is initiated and remains set as long as the compressor is running. See: Operating State in Chapter 9.

Safety On: This coil and discrete are set when the cumulative surge count is greater than zero, thus indicating the Safety On response has increased the margin of safety, and is cleared when that count is reset. This coil can only be cleared, which resets that count and response to zero. See: Surge Counters in Chapter 6.

Tracking: This discrete is set only when this controller is operating as a backup to another and is not affected by the output tracking feature. See: Redundant Control in Chapter 2.

Tran Fail: This discrete is set when any analog input signal falls outside of its transmitter testing limits. See: Transmitter Testing in Chapter 3.

Input and Holding Register Descriptions

Actuator CS: This holding register reports the actuator control signal, which is the intended value of analog OUT1 when that signal is used to manipulate the recycle valve. In contrast to the Displayed OUT input register, it is unaffected by the Recycle Valve Direction. If the Automatic coil is cleared, you can directly control the ACS by writing to this register. See: Actuator Control Signal in Chapter 8.

Analog Output 2: This input register reports the intended value of analog OUT2. See: Analog Outputs in Chapter 3.

Channel #: These input registers report the values of the corresponding analog input signals. Any channel configured as an Offset Zero Input is compensated for a twenty percent offset. See: Signal Variables in Chapter 3.

DEViation: This input register reports the deviation of the operating point from the surge control line. See: Surge Control Line in Chapter 6.

Displayed OUT: This input register reports the value displayed by the OUT readout. It will be either the same as or the complement of the Actuator CS holding register, depending on the Recycle Valve Direction [MODE:A REV]. See: Actuator Control Signal in Chapter 8.

Flow: This input register reports the digits of the Displayed Mass Flow calculated variable, prior to inserting the decimal point. See Displayed Flow in Chapter 4.

Initial b: This holding register reports the Initial Surge Control Bias [SPEC:A b 1], and writing to it changes the value of that parameter. See: Surge Control Line in Chapter 6.

Pd Limit: This holding register reports the Maximum Discharge Pressure [COND:A SP 2], and writing to it changes the value of that parameter. The Limit bit is set if that variable (CH2) is above this limit. See: Pressure Limiting in Chapter 6.

Ps Limit: This holding register reports the Minimum Suction Pressure [COND:A SP 3], and writ-ing to it changes the value of that parameter. The Limit bit is set if that variable (CH3) is below this limit. See: Pressure Limiting in Chapter 6.

Param CRC: This input register reports the 16-bit checksum for the controller’s present set of configuration and tuning parameters. See: Parameter Checksum in Appendix B.


Pressure Ratio: This input register reports the ratio of the discharge and suction pressures. See: Compression Ratio in Chapter 4.

Received Flow: see Reported Flow.

Reported Flow: In a multisection compressor application, this input register reports the flow measurement (∆Po,r / 2 or W2/ 2) or series load balancing parameter (L) this controller is sending to its companions and the Received Flow register reports the reported flow of the Adjacent Section Controller [MODE:A SS 5]. See: Reported Flow in Chapter 7.

Ss Denominator: see Ss Numerator.

Ss Numerator: This and the Ss Denominator input registers report the numerator (for example, K • Ps • hr / 2) and denominator (generally, ∆Po,s /2) of the selected fA mode, which jointly indicate how closely the compressor is operating to its surge limit. If the controller is properly tuned, the compressor will not surge unless the numerator exceeds the denominator (that is, when Ss > 1). See: Application Function in Chapter 5.

Sigma: This input register reports the polytropic head exponent, provided the chosen fA Mode calculates that variable. See: Polytropic Head Exponent in Chapter 4.

SLL Coefficient: This holding register reports but cannot change the Surge Limit Line Coeffi-cient [SPEC:A K] parameter. See: Application Function in Chapter 5.

Speed: This input register reports the normalized rotational speed of the compressor. See: Rotational Speed in Chapter 4.

Surge Count: This input register reports the number of surges detected since the cumulative surge count was last cleared. See: Surge Counters in Chapter 6.

Temperature Ratio: This input register reports the Temperature Ratio calculated variable. See Temperature Ratio in Chapter 4.

Total b: This input register reports the total margin of safety between the surge limit and surge control lines, obtained by summing the Initial Surge Control Bias, the derivative response, and the accumulated Safety On response. See: Surge Control Line in Chapter 6.


Printed in U.S.A.



U

DS301/O Series 3 Plus Antisurge Controller Operator Interface Specification

Description

The Antisurge Controller’s Front Panel features four Alphanumeric Readouts, ten active LED Indicators, and eight Control Keys. It also includes a beeper, the pitch of which can be changed by holding down the SCROLL key and pressing the Raise or Lower key.

Series 3 Plus

Antisurge Controller Operator Interface Description

Product Revision: 756-004


DISPLAY

SCROLLMENU

DISPLAYLIMITSURGE

COUNT

∆

∇

AUTO

MAN

RESETSAFETY

ON

Manual

Auto

RT

SO

Limit

Tracking

Fault

TranFail

Fallback

ComErr

DEV

OUTALT

Antisurge Controller AUX

.000

9.3

Status RUN

Note:Cross-references are to the Series 3 Plus Antisurge Controller user manual [IM301]. In pdf versions of this document, each element in the above illustration is linked to the corresponding description.

September 2005 Page 1 of 8 DS301/O (6.1.1)

AlphanumericReadouts

The alphanumeric readouts, which can be alternately brightened and dimmed by simultaneously pressing the Raise and DISPLAY LIMIT keys, have the following functions:

DEV The three-digit Deviation readout normally displays the deviation of the operating point from the Surge Control Line (see Chapter 6). Positive values indicate an acceptable margin of safety, negative values indicate unsafe operation.

This readout can also display the denominator of the Application Function or the process variables of any Limiting Control Loops.

ALT The three-character Alternate readout is normally blank. However, it will display “POC” whenever the recycle flow rate is elevated by the Performance Override (see Chapter 6) feature and will display the number of surges the Safety On algorithm has detected whenever the DISPLAY SURGE COUNT key is held down.

This readout can also display the numerator of the Application Func-tion or the set points of any Limiting Control Loops.

OUT The three-digit Output readout normally displays the Actuator Con-trol Signal, which reflects both the actual output signal and control valve position, but is not a measurement of either:

• When using Output Reverse (see Chapter 8), OUT will display 100 minus the actuator control signal.

• When using Valve Dead Band Compensation (see Chapter 8), the displayed value will jump if the control action reverses.

• In a Valve Sharing (see Chapter 7) application, the position of the recycle valve is displayed by the primary Antisurge Controller and the OUT readouts of all secondary controllers are blank.

If the RESET key is held down, this readout will display the anti-surge control response. That signal represents the intended recycle or blow-off flow, prior to any output transformations.

AUX The 12-character AUXiliary readout displays a variety of controller and process information.

By default, it displays the Status (operating state) of the controller. Provided they are enabled, pressing the MENU key once selects the Measured Variables menu, while pressing it a second time selects the Calculated Variables menu. You can cycle through the enabled variables in any of these groups by pressing the SCROLL key.

If Auxiliary Display Reset [MODE:D LOCK 9] is enabled, this read-out will revert to displaying the operating state 60 seconds after the MENU or SCROLL key was last pressed.

If the DISPLAY LIMIT key is held down, this readout will indicate which of the Limiting Control Loops’ variables are being displayed.


Status The Operating State (see Chapter 9) of the controller displays as one of the following:

• Status RUN indicates the antisurge valve is being modulated to protect a running compressor from surge.

• Status STOP indicates a normal shutdown has ramped the anti-surge valve open.

• Status ESD indicates an emergency shutdown has opened the antisurge valve as fast as possible.

• Status OFF indicates this controller is modulating its valve to sat-isfy the recycle requirements of a companion valve-sharing con-troller, even though its own compressor is shut down.

• Status PURGE indicates the valve is being held fully closed to allow residual process gas to be flushed from the compressor.

• Status TRACK indicates this controller is operating as a redun-dant backup for another Antisurge Controller or is tracking a des-ignated analog input.

Pressing the SCROLL key while any of the above is being displayed cycles through the following variables:

• DGI= 1234567, where each digit appears if that discrete input is asserted or is replaced by an underscore if it is not.

• DGO= 12345, where each digit appears if that discrete output is energized or is replaced by an underscore if it is not.

• Total B=##.#, where ##.# is the distance between the surge limit and control lines.

• f1(X)= #.##, f2(X)= #.##, f3(X)= #.##, or f5(X)= #.##, where the displayed numbers (#.##) are the results of the corresponding proximity-to-surge Characterizing Functions (see page 64) when they are being calculated. Whenever a particular characterizer is not being calculated, its result will display as “–.– –”.


ApplicationFunction

When the RESET key is held down, the ALT readout will display one-half of the numerator of the chosen proximity-to-surge Applica-tion Function (see Chapter 5), while the DEV readout will display one-half of its denominator. For example, if fA Mode 31 is selected, ALT would display K· f1(Rc)·Ps /2 and DEV would display ∆Po,c /2.

This provides an alternate indication of how closely the compressor is operating to its surge limit. If this ALT readout is greater than this DEV readout, the compressor is either in surge or the controller is incorrectly tuned.

Limiting ControlLoops

If you have enabled one of the Pressure Limiting (see Chapter 6) control loops, its status can be determined by holding down the DIS-PLAY LIMIT key. The DEV readout will then display that pressure, the ALT readout will show its set point, and the AUX readout will identify the displayed pressure (discharge or suction). If both limiting loops have been enabled, the readouts will alternate between them each time you press the DISPLAY LIMIT key.

For example, if only discharge pressure limiting is enabled, pressing DISPLAY LIMIT would always display that pressure on the DEV readout, its limiting control threshold on the ALT readout, and “Dis-charge” in the AUXiliary readout.

Provided these pressures are directly measured (via CH2 and CH3), their limiting readouts use the same scaling as the corresponding Measured Variables. If either is calculated from the other and the pressure rise across the compressor, its limiting readouts are scaled as percentages.


MeasuredVariables

The ability to display each of the Measured Variables (see Chapter 3), its label, and its numeric format are independently configured. Their default labels are listed in the following table:

If one of these variables is currently displayed, pressing SCROLL repeatedly will cycle through all of the enabled measured variables. The last one selected will be the first one displayed the next time you press MENU while the controller STATUS is displayed.

CalculatedVariables

As described on page 60, this menu can be configured to display any of the following calculated variables:

• Rc is the Compression Ratio.

• Rt is the Temperature Ratio.

• Hpr is the Reduced Head.

• Sigma is the Polytropic Head Exponent.

• Speed is the Displayed Speed.

• Flow is the Displayed Flow.

• UsrQ is the Displayed Net Flow.

As with measured variables, each of these readouts can also be independently enabled or disabled, displaying one calculated vari-able allows you to SCROLL to the others, and the last one displayed is the first shown the next time you invoke this MENU.

In the event that one or more of the inputs used to calculate these variables fail, the controller can substitute default values for either those inputs or the calculated variable (see Fallback Strategies on page 67). The resulting fallback value would then be displayed.

Input Label Input Label

CH1 ∆Po CH5 D Temp

CH2 D Press CH6 S Temp

CH3 S Press CH7 Chan 7

CH4 Speed CH8 Chan 8


LED Indicators The ten active LED indicators have the following functions:

One of these LEDs will always be lit:

• The green Auto LED lights to indicate automatic operation. It flashes if the default output fallback strategy is active.

• The yellow Manual LED lights to indicate manual operation. It flashes when operating in manual with Manual Override enabled (no automatic protection).

You can toggle between these modes by pressing the AUTO/MAN key. Automatic or manual operation can also be selected via serial communications.

If the controller is being manually operated, the yellow RT LED will be lit when the margin of safety is below the threshold for the Recy-cle Trip response and will stay on only until an adequate margin of safety is restored. If the controller is operating automatically, the RT LED remains lit until the Recycle Trip response decays to zero, even if an adequate margin of safety has been restored.

If the red SO LED is lit, the Safety On response has detected one or more surges and increased the surge control margin to prevent additional surging. You can determine how many surges were detected by pressing the DISPLAY SURGE COUNT key. The SO LED will remain on until the RESET key is pressed.

The yellow Limit LED is lit when either the discharge pressure is above its threshold or the suction pressure is below its limit. This will increase the recycle rate above the level needed for surge protec-tion alone. The DISPLAY LIMIT key can be used to display the value and set point of each limiting variable.

When redundant controllers have been installed, the green Tracking LED of the active controller (the one actually controlling the com-pressor) will be off and that of the tracking controller will be lit. It will flash if Output Tracking (see Chapter 8) is active or if the Remote Low Output Clamp (see Chapter 8) is above the internal Low Output Clamp, even if the control signal is above both clamps.

The red TranFail LED is lit when any analog input signal is beyond its Transmitter Testing (see Chapter 3) range (the Transmitter Sta-tus Test [MODE:D ANIN –] will identify the offending inputs).

The yellow Fallback LED is lit when one of the controller’s Fallback Strategies (see Chapter 5) is being used, usually because a required analog or serial input has failed (some insight can be gained by examining the TranFail and ComErr LEDs).

Manual

Auto

RT

SO

Limit

Tracking

TranFail

Fallback


The red ComErr LED is lit when the controller fails to detect an expected transmission on its Port 1 or Port 2 serial communication network. The exact meaning of this condition depends on which fea-tures are enabled (for example, load-sharing, performance override control, or speed tracking). The offending port can be identified and additional diagnostic information obtained by using the Serial Port 1 Test [MODE COMM – 3] and Serial Port 2 Test [MODE COMM – 2].

The red Fault LED is lit when an internal fault has been detected, as described in the Fault Indicators section in Chapter 8 of IM300/H. If this LED is lit but the Fault relay is not de-energized, check the cable connecting the Front Panel to the CPU PCB for loose connections.

ComErr

Fault

Caution:The controller’s output signal is totally unpredictable when the Fault LED is lit. Process disruptions or damage can result if it is not imme-diately disconnected from your process.


Control Keys The momentary-contact pushbuttons have the following functions:

The AUTO/MAN key toggles the controller between automatic and manual operation (the green Auto or yellow Manual LED will light to indicate which mode is selected).

The Raise and Lower keys vary the actuator control signal when manual operation is selected. Momentarily pressing the Raise key will increment that signal by 0.1 percent, while holding it down increases the output in steadily larger increments (it takes about 20 seconds to change the control signal by a full 100 percent). The Lower key reduces the output in a similar fashion.

Each time a surge is detected, the controller increases the surge control margin by adding the Safety On Incremental Bias. Pressing the DISPLAY SURGE COUNT key temporarily displays that surge count in the ALT readout, while pressing the RESET SAFETY ON key resets it to zero and restores the original surge control margin.

If RESET SAFETY ON is held down, the ALT and DEV readouts will display the numerator and denominator of the Ss proximity-to-surge variable, and the OUT readout will display the control response prior to any control valve compensations. Because this key also resets the Safety On response, however, you should avoid viewing these variables while the SO indicator is lit.

If the DISPLAY LIMIT key is held down, the DEV and ALT readouts will display the value and set point for one of the limiting variables, while the AUX readout displays “Discharge” or “Suction” to indicate which of those pressures is being displayed.

If both limiting loops are enabled, the displays will alternate between them each time DISPLAY LIMIT is pressed. Pressing this key does not affect the operation of the control algorithms — you can exam-ine these variables at any time without disturbing your process.

The MENU and SCROLL keys select the information displayed by the AUX readout. Pressing Menu advances that display through the available menus, while pressing Scroll advances it to the next item in the currently selected menu.

AUTO

MAN

∇

∆

DISPLAYSURGECOUNT

RESETSAFETY

ON

Warning!To avoid repeated surging, do not press RESET SAFETY ON while the SO LED is lit unless the causes of the surging have been identified and corrected.

DISPLAYLIMIT

MENU SCROLL


Printed in U.S.A.



U

DS301/V. Series 3 Plus Antisurge Controller Revision History

This data sheet describes the changes to each standard release of this controller. Cross-references are to the

Antisurge Controller

[IM301] instruction manual.

750-001

CRC: A9C5, ID Code: 0; Released: October 10, 1991

This was the initial Series 3 Plus version of the Antisurge Controller.

750-002

CRC: 085A, ID Code: 1; Released: November 5, 1991

Pressure Limiting Beginning with this revision, the Limit LED will light and any Limt relays will trip only if the recycle rate has been increased by one of the pressure limiting control loops. In the initial release, those indi-cators were set whenever either pressure was beyond its limiting control threshold, even if the resulting control action did not increase the recycle rate above that calculated by the surge protection loop.

In addition, controllers equipped with this revision or later will iden-tify and display the value and set point of the out-of-range pressure when the DISPLAY LIMIT key is pressed while the Limit LED is lit. In the initial release, that function was not implemented.

750-003

CRC: 684B, ID Code: 2; Released: November 11, 1991

This software revision fixed two minor parameter entry problems.

751-001

CRC: AFF5, ID Code: 9; Released: July 31, 1992

Analog Output Beginning with this revision, the second analog output’s function is defined by the

Second Output Assigned Variable

. In prior versions, both analog outputs always had the same function.

Discrete Outputs Beginning with this revision,

Relay Assigned Function

s have signed values. When the associated condition is detected, a relay with a positive function will energize while one with a negative function will de-energize. In prior versions, the assigned condition always ener-gized the relay.

In addition, this revision added the Surge Event (Surg) and Valve Open (Open) relay functions.

Series 3 Plus

Antisurge Controller Revision History

September 2005 Page 1 of 10 DS301/V (6.1.2)

Fallback Strategies Beginning with this revision, the controller will continuously calculate a filtered control signal value if the

Fallback Minimum Recycle

is set to zero. When this fallback is triggered, the actuator control signal is then initialized to that filtered value.

In addition, fA modes using discharge flow measurements were modified to respond to P

d

failures the same way as modes using suction flow measurements respond to P

s

failures.

Front-Panel Readouts Beginning with this revision, the AUXiliary readout displays the oper-ating state as “Status TRACK” when redundant tracking is active and the compression ratio is displayed as ##.# (in prior versions, the displayed #.## value could not exceed ten).

This version also added the Displayed Mass Flow (Flow) calculated variable and the parameters for enabling and scaling its readout.

In addition, the Engineering Panel sequence for defining measured variable labels was modified to allow reverse scrolling by pressing the minus key.

Load Sharing In prior versions, the gain for an Antisurge Controller’s primary capacity control response varied as a function of S and two range parameters [

β 3 and β 4]. Beginning with this revision, that gain is always either zero or the Recycling Gain, depending in part on whether S is above the β 3 threshold, and there is no β 4 parameter.

This revision also introduced series load-balancing based on an R variable calculated as the product of S (proximity to surge) and W2 (mass flow). In prior versions, load-balancing equalized proximity to surge in both series and parallel compressor networks.

Loop Decoupling Beginning with this revision, loop-decoupling will only increase the recycle flow rate in response to increases in the companion control-ler Antisurge PI and RT responses. A controller that has selected the performance override response of a Performance Controller will report no change in its PI response.

Modbus Beginning with this revision, Modbus While Tracking can be enabled to allow a host to communicate with tracking controllers. In prior ver-sions, only active controllers could respond to host requests.

In addition, this revision added the Limit, Fallback, Run, and DO State discrete bits, Surge Count, Param CRC, Pressure Ratio, Tem-perature Ratio, Speed, Analog Output 2, Flow, and Reported Flow input registers, and Pd Limit and Ps Limit holding registers.

Multisection FlowRates

Beginning with this revision, controllers using fA Modes 31 and 32 can receive their flow measurements from an Adjacent Section Con-troller. In prior versions, fA Mode 34 or 35 had to be used for such applications even if there was no sidestream.


751-002 CRC: A0FF, ID Code: 14; Released: December 21, 1992

Configuration Beginning with this revision, three alternate sets of parameter val-ues can be stored and recalled. Prior versions did not support any alternate sets.

Fallback Strategies Beginning with this revision, input failures trigger the default output fallback only if the controller is operating in its Run state.

Manual Operation Beginning with this revision, the actuator control signal cannot be less that the remote low output clamp while the controller is being manually operated. In prior versions, you could manually reduce the recycle rate below that level.

752-001 CRC: 8194, ID Code: 26; Released: July 9, 1993

Cold-Recycle Control Beginning with this revision, an Antisurge Controller can be config-ured for this application by selecting fA Mode 00. Previously, this function could only be performed by a Performance Controller.

Configuration Beginning with this revision, discrete input D7 can be set up to recall the first or second alternate parameter set as it is set and cleared.

Also, the Enable Reconfiguration [MODE LOCK 5 1] procedure is automatically terminated after 30 minutes of keyboard inactivity.

Control Lines Beginning with this revision, the Control Line Argument can be any analog input or the calculated flow measurement. In prior versions, it could only be ∆Po,c.

Front-Panel Readouts Beginning with this revision, the AUXiliary readout of a primary valve-sharing controller displays “Status OFF” when its own com-pressor stage is shut down but it is operating in the Run state to protect another section that is running.

Also beginning with this revision, measured variables can have neg-ative values and the compression ratio is displayed using a four-digit (##.##) format. In prior versions, measured variables could only be positive and Rc was displayed using only three digits (#.## in 750 versions, ##.# in 751 versions).

Load Balancing This revision modified the series load-balancing algorithm so the Antisurge Controller calculates only W2 (mass flow), rather than the product of that variable and S (proximity to surge) calculated by revi-sion 751 controllers.

Manual Operation Beginning with this revision, automatic operation is restored if the controller detects any condition that would trigger a shutdown.

Mass Flow Rates Beginning with this revision, the compensating pressure and tem-perature could have values as high as 10,000. In prior versions, that upper limit was 1,000.

Output Tracking Beginning with this revision, the actuator control signal can be con-figured to track an analog input when the D4 discrete input is set.


Pressure Limiting Beginning with this revision, controllers using fA Mode 01 or 02 can be configured to limit their ∆Pc (PV2) input signal. In prior versions, limiting control was not available with those Application Functions.

Proximity-to-Surge This revision introduced fA Modes 43 and 44 and the constant-sigma option that can be enabled for either of those Application Functions or fA Mode 42.

Also beginning with this revision, sigma can be used as the argu-ment for the general characterizer by disabling the f5 Argument. In prior versions, that argument had to be an analog input signal.

Recycle Balancing Beginning with this revision, this function can be implemented via either Port 1 or Port 2 communication. In prior versions, only the Port 1 method was available.


Beginning with this revision, the variable low clamp is ignored if its analog input has failed.

752-002 CRC: 4AC5, ID Code: 38; Released: December 23, 1993

Fallback Strategies Beginning with this revision, the default output fallback (fD 31) will be triggered if a controller using fA Mode 31 or 32 is configured to use but fails to receive a valid adjacent section flow measurement.

In addition, this revision extended the default compression ratio (fD 33) and sigma (fD 34) fallbacks to fA 43 and 44 (which were intro-duced in revision 752-001).

Manual Operation Beginning with this revision, the detection of a shutdown condition will restore automatic operation only if Manual Override is disabled.

Modbus Beginning with this revision, each input register can also be read (but not changed) at an address calculated by adding its offset to the address of the last defined holding register.

Surge Protection Beginning with this revision, the detection of a surge will also trigger a Recycle Trip response, thus increasing both the safety margin and recycle flow rate. In prior revisions, a surge that did not move the operating point to the left of an incorrectly defined RTL would not increase the recycle flow.

In addition, this revision added the Maximum Ss Derivative [PID:A Td 0 •] procedure as a tuning aid for the Derivative and derivative Recycle Trip responses.

753-001 CRC: DB2F, ID Code: 48; Released: August 8, 1994

Discrete Outputs This revision added the Run State (Run) relay assignment.

Input Signal Values Beginning with this revision, this test will time out and clear the dis-play after five minutes of inactivity. Prior versions timed out after about 45 seconds.


Mass Flow Rates Beginning with this revision, the result of the square root function can be as high as four, which allows its argument to be as high as 16. In prior versions, both values could be no greater than one.

Modbus Coils 00001 to 00010 are undefined in all Series 3 Plus Controllers. For all prior releases, any attempt to read those coils would return an error. Beginning with this revision, such reads return zeroes.

Program Downloading Beginning with this revision, software cannot be downloaded to a redundant tracking controller with Modbus While Tracking disabled.

Recycle Trip Indicators Beginning with this revision, the RT LED can light and any RT relays can be tripped only if the controller is operating in its Run state.

Shutdown This revision introduced the normal shutdown sequence, which ramps the recycle valve open and displays the resulting shut-down state as “Status STOP”. Following an emergency shutdown, the operating state will now display as “Status ESD”. Prior versions always executed an emergency shutdown and displayed the shut-down state as “Status STOP”.

Valve Sharing Beginning with this revision, the primary controller can select its Purge state only if all secondary controllers are operating in their Shutdown states.

753-002 CRC: F4C2, ID Code: 59; Released: March 31, 1995

Fallback Strategies Beginning with this revision, the default output fallback (fD 31) does not select manual operation (instead of lighting the Manual LED, it now flashes the Auto indicator).

Conditions that would otherwise trigger the minimum flow fallback (fD 32) will now trigger fD 31 if fD 32 is disabled.

Also, fD 31 will now be triggered if a controller using fA Mode 34 or 35 fails to receive a valid adjacent section flow measurement. In prior versions, controllers using these fA modes would calculate proximity to surge from the Default Adjacent Section Flow unless that fallback was disabled.

Modbus Beginning with this revision, the Surge Limit Line Coefficient [SPEC:A K] can no longer be changed by writing to the SLL Coeffi-cient holding register.

Changes were also made to improve communication over two-wire RS-485 connections.

Surge Detection Beginning with this revision, operating to the left of the Safety On control line will repeatedly increment the surge count at the Safety On Repeat Interval. In prior versions, that count was incremented once each time the operating point crossed to the left of the SOL.

Warning! A version 753 (or earlier) controller will respond to a purge request unless it is operating in the Tracking state.


754-001 CRC: 04CD, ID Code: 91; Released: October 11, 1996

Analog Outputs This revision added the Flow and UsrQ analog OUT2 functions.

Calculated Variables This revision added the Flow Variables Decimal parameter and Available Flow (UsrQ) variable. In addition, it calculates Flow from ∆Po,c when the Mass Flow Input is disabled (Off).

Constant OutputFallback

Beginning with this revision, the Constant Output Fallback sets the actuator control signal to the higher of the filtered control signal value or the Fallback Minimum Recycle. In prior versions, this fall-back initialized that signal to its default value unless it that default was zero, in which case the filtered value was used.

In addition, if fA 00 is selected, this fallback is triggered by a flow failure in any companion controller; if fA 34 is selected, it is also trig-gered by a failure of the preceding section pressure (CH5); in a valve-sharing master with the Valve-Sharing Fallback disabled, it is now triggered by loss of communication with any companion.

Derivative Response This revision added the CRD Dead-Zone Bias [PID:A r 3]. In prior versions, the derivative response was strictly proportional to the proximity-to-surge derivative.

Discrete Outputs This revision added the Manual Override (MOR) and Position Fail-ure (PosF) relay assignments.

Load Sharing Beginning with this revision, the series load-balancing parameter is a function of proximity-to-surge, mass flow, and a user-specified load variable. In prior versions, it was a function of proximity-to-surge and mass flow only.

Loop Decoupling Beginning with this revision, loop-decoupling can never decrease the recycle flow rate.

Manual Override Beginning with this revision, the Manual LED flashes and any MOR relays are set if the controller is manually operated with Manual Override enabled. In prior versions, there was no indication that automatic surge protection had been overridden.

Also beginning with this revision, the Limit LED will light and any Limt relays will trip if either the suction or discharge pressure is beyond its limiting control threshold during manual operation.

Minimum Flow Fallback Beginning with this revision, the Minimum Flow Fallback is triggered by a Speed or f5 Argument failure if that variable is required by the selected fA Mode and the Speed or Function 5 Fallback is disabled.

Multisection FlowRates

Beginning with this revision, controllers using fA Mode 33 can receive their flow measurements from an Adjacent Section Control-ler and will use the Reported Flow Characterizer to calculate the flow transmitted to companion controllers. In prior versions, this was true of controllers using fA 31 and 32 but not fA 33.

Proximity-to-Surge This revision introduced fA Modes 61, 62, and 64 through 69.


Purge State Beginning with this revision, the purge response is triggered only if the purge input is asserted while the Stop state is selected. In prior versions, this response could be triggered in the Run state.

Rotational Speed Beginning with this revision, the controller can receive its speed sig-nal from a version 954-001 (or higher) Performance Controller. It can also base its operating state on the rotational speed (and that input can be monitored and recorded) even if that signal is not used by the selected Application Function. In prior versions, the speed could be received serially only from a Speed or Fuel Controller and the specified speed source was ignored unless required by the selected fA Mode.

Safety On Response Beginning with this revision, the surge count can be reset to zero by asserting discrete input D5.

Surge Control Line Beginning with this revision, the value 4 selects the rotational speed as the Control Line Argument, even if it is received from another controller via serial communications. In prior versions, that value always selected analog input CH4.

Valve Sharing Beginning with this revision, the actuator control signal of a second-ary valve-sharing controller will track that of the designated primary controller. In prior versions, the value of the OUT1 signal was not defined in such applications.

754-002 CRC: FDE1, ID Code: 99; Released: May 15, 1997

ALT Display Beginning with this revision, “POC” is displayed by the ALTernate readout whenever the recycle flow rate is elevated by the perfor-mance override feature.

Input Signal Values In previous versions, the Signal Values Test [MODE TEST 4] read all of the controller’s analog inputs just once. The displayed values would not subsequently change no matter how long or how many times they were displayed (unless the test was terminated and restarted). Beginning with this revision, the currently-displayed input’s value is updated continually.

Program Downloading In general, a new control program can be downloaded to an Anti-surge Controller only while it is being manually operated. Beginning with this revision, however, new software can be downloaded into a secondary valve-sharing controller while it is operating automati-cally. In prior versions, downloading could be initiated only while such controllers were being manually operated.

755-001 This major revision was skipped in order to bring the numbering for this product into synchronization with that for the Speed Controller.


756-001 CRC: 60E5, ID Code: 132; Released: February 5, 1999

Dual Flow Transmitters Beginning with this revision, an application that requires frequent or sustained operation at low orifice pressure drops can automatically select either of two differently-spanned flow inputs.

Limiting VariableDisplays

Beginning with this revision, the front-panel readouts of the limiting variables and control thresholds use the same scaling as their mea-sured variable readouts. In prior versions, these variables were always displayed as percentages.

Modbus This revision will return a normal response if a host attempts to write to an undefined coil or to set the Safety On coil (which can only be cleared). However, such writes will not affect the controller’s opera-tion. In prior versions, writing to such coils would return an error.

In addition, the Port 2 Fail discrete is now set only if the controller expects to receive transmissions from a Station Controller and does not. In prior versions, it was set if the controller failed to detect Port 2 activity, even if none was expected.

Operating StateRequests

Beginning with this revision, a shutdown will be initiated if requested by either a discrete input or a designated Stop/Purge Companion controller. In prior versions, designating a Stop/Purge Companion disabled this controller’s operating state discrete inputs.

Proximity-to-Surge This revision introduced fA Mode 63, which is based on the com-pression ration and an aftercooler flow measurement.

Surge Counters Beginning with this revision, the controller can maintain both event and cumulative surge counters. Prior versions maintained only a cumulative surge count.

756-002 CRC: 0B54, ID Code: 168; Released: August 29, 2002

Front-Panel Readouts This revision added the discrete I/O status, Total B, and character-izer result variables to the AUXiliary readout Status menu.

Modbus This revision added the POC Active discrete bit.

Pressure Limiting Beginning with this revision, a controller using fA Mode 01 or 02 can limit its CH3 process variable (PV3) even though it is not used by those Application Functions.

756-003 CRC: BCBB, ID Code: 179; Released: December 24, 2003

This revision fixed two minor Auxiliary readout problems.


756-004 CRC: 4DF8, ID Code: 196; Released: July 1, 2005

Fallback Strategies Beginning with this revision, the default output fallback strategy ramps the output to the configured target (previously, it triggered a step change).

In addition:

• Failure of the Output Tracking input now ramps the output to an averaged (rather than the last good) value of that input.

• The Minimum Flow, Speed, and Function 5 fallback strategies are now supported when fA mode 51 is selected.

Front-Panel Readouts This revision added reduced head (Hpr) to the AUXiliary readout Calculated Variables menu.

Load Sharing Beginning with this revision, the primary capacity control response will ignore station control signal step changes above 10 percent.

Modbus Beginning with this revision, a NAK exception response is no longer returned when a host tries to change the output signal while the con-troller is operating automatically.


Beginning with this revision, the remote low clamp input is ignored during manual operation if the Manual Override parameter is On.



Printed in U.S.A.



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FM301/C. Series 3 Plus Anti-surge Controller Configuration Worksheet

COND:A GROUP

β

3

β

5

CONST 1

CONST 2

CONST 3

CONST 4

CONST 5

CONST 6

CONST 7

CONST 8

LVL 1

LVL 2

LVL 3

OUT 1

OUT HIGH

OUT LOW

SP 2

SP 3

X 1 # 0.000 10.00

f(X) 1 #

X 2 # 0.000 10.00

f(X) 2 #

X 3 # .000 1.000

f(X) 3 #

X 4 # 0.000 1.000

f(X) 4 #

X 5 # 0.000 1.000

f(X) 5 #

X 6 # 0.000 1.000

f(X) 6 #

M #

0 1 2 3 4 5 6 7 8 9

Series 3 Plus

Antisurge Controller Configuration Worksheet

Customer: CCC No.:

Completed By: Tag No.:

Date: Serial No.:

Software Rev.: 756-001 Checksum:

Service:

Controller ID: Computer ID:

February 1999 Page 1 of 4 FM301/C (6.0.0)

Series 3 Plus

Antisurge Controller Configuration Worksheet Configuration Worksheet

MODE:A GROUPANIN 4

fA

fB 1

fB 2

fB 3

fB 4

fB –

fC 1

fC 2

fC 3

fC 4

fC 8

fC 9

fD 2

fD 9

fE 4

fE 5

MOR

MVAR 2

MVAR 3

REV

SS 2

SS 3

SS 4

SS 5

SS 6 1

SS 6 2

SS 8

SS 9

SS –

SS HIGH

fD 3 #

SS 0 #

SS 1 #

SS 7 # 1 2 3 4 5 6 7 8 9

PID:A GROUPG

Kr 1

Kr 2

Kr 3

PB 1

PB 2

PB 3

r 1

r 3

Td 0

Td 1

Tf 1

Tf 2

SPEC:A GROUPA 1

A 2

A 3

A 4

A 5

b 1

b 2

b 3

C 0

C 1

C 2

C 3

C 4

C 5

d 1

K

RT

SO

TL


Series 3 Plus Antisurge Controller Configuration Worksheet Configuration Worksheet

COND:D GROUPβ 0

CONST 0

CONST 1

CONST 2

CONST 3

CONST 5

LVL 5

OUT 2

BIAS #

GAIN #

DISPLAY 0 #

DISPLAY 0 # –

DISPLAY 0 # •

DISPLAY 0 # HIGH

DISPLAY 0 # LOW

DISPLAY 1 #

DISPLAY 1 # •

DISPLAY 1 # HIGH

X 2 # 0.000 1.000

f(X) 2 # 0 1 2 3 4 5 6 7 8 9

MODE:D GROUPCOMM 2

COMM 3 baud

COMM 3 parity

COMM 4 baud

COMM 4 parity

fD 1

fD 2

fD 3

fE 1

LOCK 0

LOCK 1

LOCK 2

LOCK 3

LOCK 6

LOCK 7

LOCK 9

AN IN #

AN IN # HIGH

AN IN # LOW 1 2 3 4 5 6 7 8

RA #

jumper # CR1 CR2 CR3 CR4 CR5JP5 JP6 JP7 JP8 JP9


Series 3 Plus Antisurge Controller Configuration Worksheet Configuration Worksheet


Printed in U.S.A.



U

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FM301/L. Series 3 Plus Antisurge Controller Configuration Planner


(see Chapter 5 of IM301)


[MODE:A fA] see Appendix F of IM301

Surge Limit Line Coefficient

[SPEC:A K] .000 to .999

DEV Filter Constant

[PID:A Tf 1]

≤

99.9 sec

Y Coordinate Characterizer

[COND:A f(X) 1 # and X 1 #] 0.00 to 9.99

R

c

: 0.00 10.00

f

1

(R

c

):

0 1 2 3 4 5 6 7 8 9

X Coordinate Characterizer

[COND:A f(X) 3 # and X 3 #] 0.00 to 9.99

N: .000 1.000

f

3

(N):

0 1 2 3 4 5 6 7 8 9

f

5

Argument

[MODE:A SS 9] Off for

σ

/ 1 to 8 (Channel #)

General Characterizer

[COND:A f(X) 5 # and X 5 #] 0.00 to 9.99

X: .000 1.000

f

5

(X):

0 1 2 3 4 5 6 7 8 9

Fallback Strategies

(see Chapter 5 of IM301)

Default Output Fallback

[MODE:A fD 3 1] Off / On

Fallback Minimum Recycle

[COND:A CONST 1]

≤

99.9 %

Minimum Flow Fallback

[MODE:A fD 3 2] Off / OnDefault Minimum Flow [COND:A CONST 2] ≤ 99.9 %

Compression Ratio Fallback [MODE:A fD 3 3] Off / OnDefault Compression Ratio [COND:A CONST 3] ≤ 9.99 %

Sigma Fallback [MODE:A fD 3 4] Off / OnDefault Sigma [COND:A CONST 4] ≤ .999 %

Speed Fallback [MODE:A fD 3 5] Off / OnDefault Speed [COND:A CONST 5] ≤ 99.9 %

Function 5 Fallback [MODE:A fD 3 6] Off / OnDefault f5 Argument [COND:A CONST 6] ≤ 99.9 %

Adjacent Section Flow Fallback [MODE:A fD 3 7] Off / OnDefault Adjacent Section Flow [COND:A CONST 7] ≤ 99.9 %

Valve Sharing Fallback [MODE:A fD 3 8] Off / OnAlternate K [COND:A CONST 8] ≤ .999 %

Polytropic Head Fallback [MODE:A fD 3 9] Off / On

Series 3 Plus Antisurge Controller Configuration Planner

Customer: CCC No.: Completed By: Tag No.:

Date: Serial No.: Software Rev.: 756-001 Checksum:

Service: Controller ID: Computer ID:

January 2001 Page 1 of 8 FM301/L (6.0.1)

Series 3 Plus Antisurge Controller Configuration Planner Configuration Planner

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Calculated Variables (see Chapter 4 of IM301)

∆Pc Substitution [MODE:A SS 6 1] Off / High / Low∆Tc Substitution [MODE:A SS 6 2] Off / High / Low

Constant Sigma [MODE:A fC 2] Off / OnSigma Filter Constant [PID:A Tf 2] ≤ 999 sec

Rotational Speed Source [MODE:A ANIN 4] Off / 1 to 8 (Controller ID)Flow Element Pressure Input [MODE:A SS 8] Off / 1 to 8 (Channel #)

Low Flow Input [MODE:A SS –] Off / 1 to 8 (Channel #)

Mass Flow Rates (see Chapter 4 and Chapter 7 of IM301)Mass Flow Coefficient [COND:A β 5] ≤ 99.9

Compensating Pressure Input [MODE:D fD 2] 1 to 8 (Channel #)Compensating Pressure Offset [COND:D CONST 2] ≤ 99.9

Compensating Temperature Input [MODE:D fD 3] 1 to 8 (Channel #)Compensating Temperature Offset [COND:D CONST 3] ≤ 999

Equivalent Flow Measurements (see Chapter 7 of IM301)

Adjacent Section Controller [MODE:A SS 5] Off / 1 to 8 (Controller ID)Sidestream Flow Coefficient [SPEC:A C 3] ≤ 9.99

Main Flow Coefficient [SPEC:A C 4] ≤ 9.99Combined Flow Coefficient [SPEC:A C 5] ≤ ±9.99

Reported Flow Characterizer [COND:A f(X) 2 # and X 2 #] 0.00 to 9.99Rc: 0.00 10.00

f2(Rc): 0 1 2 3 4 5 6 7 8 9

Calculated Variable Displays (see Chapter 4 of IM301)Polytropic Exponent Display [COND:D DISPLAY 1 1] Off / OnCompression Ratio Display [COND:D DISPLAY 1 2] Off / OnTemperature Ratio Display [COND:D DISPLAY 1 3] Off / On

Rotational Speed Display [COND:D DISPLAY 1 4] Off / OnRotational Speed Coefficient [COND:D DISPLAY 1 4 HIGH] ≤ 99999

Flow Variables Decimal [COND:D DISPLAY 1 5 •] 0 to 4 (1 = ###., 4 = .###)Mass Flow Display [COND:D DISPLAY 1 5] Off / On

Mass Flow Input [MODE:D fD 1] Off / 1 to 8 (Channel #)Displayed Flow Coefficient [COND:D DISPLAY 1 5 HIGH] ≤ 99999

Net Flow Display [COND:D DISPLAY 1 7] Off / OnNet Flow Coefficient [COND:D DISPLAY 1 7 HIGH] ≤ 99999



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Control Lines (see Chapter 6 of IM301)

Initial Surge Control Bias [SPEC:A b 1] ≤ 99.9 %Control Line Argument [MODE:A fC 1] Off / 1 to 8 (Channel #)

Control Line Characterizer [COND:A f(X) 4 # and X 4 #] 0.00 to 9.99X: .000 1.000

f4(X): 0 1 2 3 4 5 6 7 8 9

Derivative Response (see Chapter 6 of IM301)

Derivative Response [MODE:A fC 3] Off / OnMaximum Derivative Response [SPEC:A b 3] ≤ 99.9 %

CRD Dead-Zone Bias [PID:A r 3] ≤ 99.9 %/160 msecCRD Time Constant [PID:A Td 0] ≤ 99.9 sec

Safety On Response (see Chapter 6 of IM301)

Safety On Incremental Bias [SPEC:A b 2] ≤ 99.9 %Safety On Line Distance [SPEC:A SO] ≤ 99.9 %

Surge Detection Method [MODE:A fD 2] Off / 1 /2 / 3 / 4Flow Rate-of-Change Threshold [SPEC:A A 1] ≤ ±99.9 %/160 msec

Flow After Pressure Time Lag [SPEC:A A 2] ≤ 9.96 secPressure Rate-of-Change Threshold [SPEC:A A 3] ≤ ±99.9 %/160 msec

Pressure After Flow Time Lag [SPEC:A A 4] ≤ 9.96 secSafety On Repeat Interval [SPEC:A A 5] ≤ 9.96 sec

Surge Event Threshold [COND:D CONST 0] ≤ 99 surgesSurge Event Duration [COND:D CONST 1] ≤ 999 sec



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Antisurge Control Response (see Chapter 6 of IM301)

General Ramp Rate [PID:A G] ≤ 9.99 rpts/min

Antisurge PI Response (see Chapter 6 of IM301)

DEV Proportional Band [PID:A PB 1] 006 to 999DEV Reset Rate [PID:A Kr 1] ≤ 99.9 rpts/min

DEV Dead-Zone Bias [PID:A r 1] ≤ 99.9 %

Recycle Trip Response (see Chapter 6 of IM301)

Recycle Trip Line Distance [SPEC:A RT] ≤ 99.9 %Derivative Recycle Trip [MODE:A fC 4] Off / On

Recycle Trip Gain [SPEC:A C 0] ≤ 99.9Maximum Recycle Trip Step Size [SPEC:A C 1] ≤ 99.9 %

Recycle Trip Repeat Interval [SPEC:A C 2] ≤ 9.96 secRecycle Trip Time Constant [PID:A Td 1] ≤ 9.99 sec

Recycle Trip Decay Rate [SPEC:A TL] ≤ 999 sec

Pressure Limiting (see Chapter 6 of IM301)

Discharge Pressure Limiting [MODE:A MVAR 2] Off / OnMaximum Discharge Pressure [COND:A SP 2] ≤ 99.9 %

Pd Proportional Band [PID:A PB 2] 006 to 999Pd Reset Rate [PID:A Kr 2] ≤ 99.9 rpts/min

Suction Pressure Limiting [MODE:A MVAR 3] Off / OnMinimum Suction Pressure [COND:A SP 3] ≤ 99.9 %

Ps Proportional Band [PID:A PB 3] 006 to 999Ps Reset Rate [PID:A Kr 3] ≤ 99.9 rpts/min

Performance Override (see Chapter 6 of IM301)

Performance Override Control [MODE:A SS 3] Off / On

Loop Decoupling (see Chapter 6 of IM301)

Decoupling Controller [MODE:A SS 0 #] Off / OnDecoupling Gain [COND:A M #] –9.99 to 9.99

Enable:

Gain: 1 2 3 4 5 6 7 8

Valve Sharing (see Chapter 7 of IM301)

Valve-Sharing Master ID [MODE:A SS 2] Off / 1 to 8 (Controller ID)

Valve Sharing Companion [MODE:A SS 1 #] Off / OnEnable:

1 2 3 4 5 6 7 8



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Networked CompressorsPrimary Capacity Control (see Chapter 7 of IM301)

Load-Sharing Controller [MODE:A SS 4] Off / 1 to 8 (Controller ID)Recycling Gain [COND:A M 0] ≤ ±9.99

Recycling Threshold [COND:A β 3] ≤ 1.99

Load Balancing (see Chapter 7 of IM301)Series Load Variable [MODE:A fC 9] Off / On

Load Balancing Variable [MODE:A fD 9] Off / 1 to 8 (Channel #)

Recycle Flow Characterizer [COND:D f(X) 2 # and X 2 #] 0.00 to 9.99CR: .000 1.000

f2(CR): 0 1 2 3 4 5 6 7 8 9

Balancing Variable Characterizer [COND:A f(X) 6 # and X 6 #] 0.00 to 9.99X: .000 1.000

f6(X): 0 1 2 3 4 5 6 7 8 9

Recycle Balancing (see Chapter 7 of IM301)Port 2 Recycle Balancing [MODE:A SS HIGH] Off / On

Recycle Balancing Controller [MODE:A SS 7 #] Off / OnEnable:

1 2 3 4 5 6 7 8

For Port 1 balancing, you must also enable the corresponding Valve Sharing Companion parameters.



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States and TransitionsOperating State Request Signals (see Chapter 9 of IM301)

Stop/Purge Companion [MODE:A fB –] Off / 1 to 8 (Controller ID)Stop Requests [MODE:A fB 1] Off / On

Purge State [MODE:A fB 2] Off / OnMinimum Flow and Pressure [COND:A LVL 1] ≤ 99.9 %

Minimum Speed [COND:A LVL 2] ≤ 99.9 %

Shutdown Configuration (see Chapter 9 of IM301)Stopping Ramp Rate [COND:A LVL 3] ≤ 9.99 rpts/min

Safety On AutoReset [MODE:A fB 3] Off / On

Manual Override (see Chapter 9 of IM301)

Manual Override [MODE:A MOR] Off / On disables automatic protectionManual While Stopped [MODE:A fB 4] Off / On to permit manual

Redundant Tracking (see Chapter 9 of IM301)Redundant Tracking [MODE:D fE 1] Off / On enables tracking

Modbus While Tracking [MODE:D LOCK 0] Off / On requires different IDs

Alternate Parameter Sets (see Chapter 9 of IM301)Remote Parameter Switching [MODE:D LOCK 3] Off / On

Alphanumeric Readouts (see Alphanumeric Readouts in DS301/O)Auxiliary Display Reset [MODE:D LOCK 9] Off / On



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Analog Inputs (see Chapter 3 of IM301)Variable:

CH1 CH2 CH3 CH4

CH5 CH6 CH7 CH8

Disabling Input Signals (see Chapter 3 of IM301)CPU Inputs Lockout [MODE:D LOCK 6] Off / On Must be OFF

Transmitter Testing (see Chapter 3 of IM301)

Analog Input High Alarm Limit [MODE:D ANIN # HIGH] ≤102.4 %Analog Input Low Alarm Limit [MODE:D ANIN # LOW] ≤102.4 %

High:

Low: 1 2 3 4 5 6 7 8

Signal Variables (see Chapter 3 of IM301)

Offset Zero Input [MODE:D ANIN #] Off / OnEnable:

1 2 3 4 5 6 7 8

Process Variables (see Chapter 3 of IM301)

Process Variable Gain [COND:D GAIN #] ≤1.000Process Variable Bias [COND:D BIAS #] ≤ 99.9 %

High:

Low: 1 2 3 4 5 6 7 8

Measured Variables (see Chapter 3 of IM301)

Measured Variable Display [COND:D DISPLAY 0 #] Off / OnMeasured Variable Label [COND:D DISPLAY 0 # –] 8 Characters

Measured Variable Maximum [COND:D DISPLAY 0 # HIGH] –9999 to 9999Measured Variable Minimum [COND:D DISPLAY 0 # LOW] –9999 to 9999

Measured Variable Decimal [COND:D DISPLAY 0 # •] 0 to 4 1 = ###., 4 = .###Enable:

Label:

High:

Low:

Decimal: 1 2 3 4 5 6 7 8



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Output Variables (see Chapter 8 of IM301)Valve Flow Characterizer [MODE:A fC 8] Off / High / LowRecycle Valve Direction [MODE:A REV] Off / On if signal-to-close valve

Valve Dead-Band Bias [COND:A OUT 1] ≤ 99.9 %Recycle High Clamp [COND:A OUT HIGH] ≤ 99.9 %Recycle Low Clamp [COND:A OUT LOW] ≤ 99.9 %

Remote Low Output Clamp [MODE:A fE 4] Off / 1 to 8 (Channel #)Output Tracking [MODE:A fE 5] Off / 1 to 8 (Channel #)

Tight Shut-Off Line Distance [SPEC:A d 1] ≤ 99.9 %

Analog Outputs (see Chapter 3 of IM301)Second Output Assigned Variable [COND:D OUT 2] Out / Flow / S / UsrQ

Valve Position Test (see Chapter 3 of IM301)Position Failure Threshold [COND:D LVL 5] ≤ 99.9 %Position Failure Delay [COND:D CONST 5] ≤ 99.9 %

Discrete Outputs (see Chapter 3 of IM301)

Relay Assigned Function [MODE:D RA #] ± function from Table 3-4function:

NO/ NC: DO1 DO2 DO3 DO4 DO5

JP5 JP6 JP7 JP8 JP9

Serial PortsID Numbers (see Chapter 3 of IM301)

Controller ID Number [MODE:D COMM 0] 1 to 8 for Port 1Computer ID Number [MODE:D COMM 0 •] 1 to 64 for Ports 2, 3, & 4

Serial Communication Formats (see Chapter 3 of IM301)

Port 2 Baud Rate [MODE:D COMM 2] 2400 / 4800 / (9600 recommended)Port 3 Baud Rate [MODE:D COMM 3] 4800 / 9600 / 19.2k

Port 3 Parity [MODE:D COMM 3] Odd / Even / NonePort 4 Baud Rate [MODE:D COMM 4] 4800 / 9600 / 19.2k

Port 4 Parity [MODE:D COMM 4] Odd / Even / None

Modbus Configuration (see Chapter 3 of IM301)

Read and Write Inhibit [MODE:D LOCK 1] Off / On for no ModbusWrite Inhibit Only [MODE:D LOCK 2] Off / On for read-only

Modbus Register Scaling [MODE:D LOCK 7] Off / On for 0-to-100 % (Port 3)


Printed in U.S.A.



U

May 2006 FM73 (3.0)

FM73

If you have questions or comments concerning the information provided in this user manual or in any of our technical documents please contact CCC’s Technical Documentation Department:

E-mail: [email protected]

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Antisurge Controller forAxial & Centrifugal Compressors [CCC Book].pdf

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Transcript of Antisurge Controller forAxial & Centrifugal Compressors [CCC Book].pdf