Anti Surge

L

®COMPRESSOR

CONTROLS

CORPORATION

PID

FT

A/D

RAM

PID

11359 AURORA AVENUE

DES MOINES, IOWA 50322, U.S.A.

PHONE 515-270-0857

FAX 515-270-1331

GLOBAL

SUPPLIERS

OF

TURBINE

AND

COMPRESSOR

CONTROL

SYSTEMS

t

®

WWW.CCCGLOBAL.COM

Using the Series 4 Antisurge Controller

Publication UM4102 (3.0)

Product Revision: 5.01

April 17, 1998

Make File: 5.1.22Database: 5.1.11

© 1987-1998, 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.

The impeller and TTC logos, Total Train Control, TTC, Recycle Trip, Safety On, and Air Miser are registered trademarks and COMMAND is a trademark of Compressor Controls Corporation. Other product names and company names mentioned herein 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:

Re. 30,329 3,951,586 3,979,655 3,994,6234,046,490 4,102,604 4,119,391 4,142,8384,486,142 4,494,006 4,640,665 4,949,2765,347,467 5,508,943 5,599,161 5,609,4655,622,042 5,699,267

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

The completeness and accuracy of this document is not guaranteed, and nothing herein should be construed as a warranty or guarantee, express 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.

Contents–1

Contents

Document Introduction . . . . . . . . . . . . . . . . . . 1-1

Products Discussed in This Document . . . . . . . . . . . . . . . 1-1

Document Content . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

Conventions Used in This Document . . . . . . . . . . . . . . . . 1-2

Reader Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Antisurge Control Overview . . . . . . . . . . . . . . . 2-1

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Principles of Surge Prevention . . . . . . . . . . . . . . . . . . . 2-3

Theory of Operation . . . . . . . . . . . . . . . . . . . . 3-1

Proximity to Surge. . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

Numerator and Denominator Modes . . . . . . . . . . . . . . . . 3-3

Control Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

Control Line Characterizer. . . . . . . . . . . . . . . . . . . . 3-9Surge Limit Line . . . . . . . . . . . . . . . . . . . . . . . . . 3-10Safety Margin (b) . . . . . . . . . . . . . . . . . . . . . . . . 3-10Surge Control Line. . . . . . . . . . . . . . . . . . . . . . . . 3-10Safety On Line. . . . . . . . . . . . . . . . . . . . . . . . . . 3-11Recycle Trip Line . . . . . . . . . . . . . . . . . . . . . . . . 3-11Tight Shutoff Line . . . . . . . . . . . . . . . . . . . . . . . . 3-11Operating Point . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

Controller Inputs and Outputs . . . . . . . . . . . . . . . . . . . . 3-13

Input/Output Configuration . . . . . . . . . . . . . . . . . . . 3-13Input/Output Fault Detection. . . . . . . . . . . . . . . . . . . 3-14Packet Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15

Process Variables . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

Measured Variables . . . . . . . . . . . . . . . . . . . . . . . 3-16Redundant Signal Selection . . . . . . . . . . . . . . . . . . . 3-17Process Variable Scaling . . . . . . . . . . . . . . . . . . . . 3-18

UM4102 (3.0) — Using the Series 4 Antisurge Controller

Contents

–2

Calculated Variables. . . . . . . . . . . . . . . . . . . . . . . 3-20Compression Ratio. . . . . . . . . . . . . . . . . . . . . . 3-20Temperature Ratio . . . . . . . . . . . . . . . . . . . . . . 3-20Polytropic Head Exponent . . . . . . . . . . . . . . . . . . 3-21Reduced Polytropic Head . . . . . . . . . . . . . . . . . . 3-21Suction Flow . . . . . . . . . . . . . . . . . . . . . . . . . 3-21Reported Flow . . . . . . . . . . . . . . . . . . . . . . . . 3-22Mass Flow Rate . . . . . . . . . . . . . . . . . . . . . . . 3-22Multisection Compressor Flow Rates . . . . . . . . . . . . 3-24

Fallback Strategies . . . . . . . . . . . . . . . . . . . . . . . . . 3-27

Adjacent Flow Fallback . . . . . . . . . . . . . . . . . . . . . 3-27Compression Ratio Fallback. . . . . . . . . . . . . . . . . . . 3-28Inlet Valve Fallback . . . . . . . . . . . . . . . . . . . . . . . 3-28Limiting Control Fallbacks . . . . . . . . . . . . . . . . . . . . 3-28Minimum Flow Fallback . . . . . . . . . . . . . . . . . . . . . 3-28Polytropic Head Fallback . . . . . . . . . . . . . . . . . . . . 3-29Run Freeze Fallback . . . . . . . . . . . . . . . . . . . . . . 3-30Sigma Fallback . . . . . . . . . . . . . . . . . . . . . . . . . 3-30Valve-Sharing Fallback . . . . . . . . . . . . . . . . . . . . . 3-30Aftercooler Temperature Failure. . . . . . . . . . . . . . . . . 3-31Discharge Pressure Failure . . . . . . . . . . . . . . . . . . . 3-31Discharge and Suction Temperature Failure . . . . . . . . . . 3-32dPo Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32Speed Failure . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32Suction Pressure Failure . . . . . . . . . . . . . . . . . . . . 3-32Guide Vane Angle Failure . . . . . . . . . . . . . . . . . . . . 3-33

Antisurge Controller Functions . . . . . . . . . . . . . . . . . . . 3-34

General PID Algorithm. . . . . . . . . . . . . . . . . . . . . . 3-37PID Span and Direction . . . . . . . . . . . . . . . . . . . 3-38PID Dead Zone . . . . . . . . . . . . . . . . . . . . . . . 3-39PID Velocity Clamps . . . . . . . . . . . . . . . . . . . . . 3-40

Antisurge PI Response . . . . . . . . . . . . . . . . . . . . . 3-40Derivative Response . . . . . . . . . . . . . . . . . . . . . . 3-41Recycle Trip Response . . . . . . . . . . . . . . . . . . . . . 3-42

Recycle Trip Derivative Response. . . . . . . . . . . . . . 3-44Recycle Trip dSs Response . . . . . . . . . . . . . . . . . 3-45PI Response During Recycle Trip . . . . . . . . . . . . . . 3-45Recycle Trip Manual Override . . . . . . . . . . . . . . . . 3-46Recycle Trip Status . . . . . . . . . . . . . . . . . . . . . 3-47Recycle Trip Test Response. . . . . . . . . . . . . . . . . 3-47

April 20, 1998

Contents–3

Safety On Response . . . . . . . . . . . . . . . . . . . . . . 3-47EAS Surge Detection . . . . . . . . . . . . . . . . . . . . . . 3-50Limiting Control Response . . . . . . . . . . . . . . . . . . . 3-52

Suction Pressure Limiting . . . . . . . . . . . . . . . . . . 3-53Discharge Pressure Limiting . . . . . . . . . . . . . . . . . 3-54Compression Ratio Limiting . . . . . . . . . . . . . . . . . 3-55

Integrated Control Features . . . . . . . . . . . . . . . . . . . 3-56Valve Sharing . . . . . . . . . . . . . . . . . . . . . . . . 3-57Pressure Override Control . . . . . . . . . . . . . . . . . . 3-60Filtered POC Response . . . . . . . . . . . . . . . . . . . 3-62Loop Decoupling . . . . . . . . . . . . . . . . . . . . . . . 3-63

Load Sharing . . . . . . . . . . . . . . . . . . . . . . . . . . 3-64Load-Sharing Response . . . . . . . . . . . . . . . . . . . 3-65Load-Balancing Response. . . . . . . . . . . . . . . . . . 3-67Recycle Balancing Response . . . . . . . . . . . . . . . . 3-67Cold Recycle (S) Control. . . . . . . . . . . . . . . . . . . 3-69

Control Element Compensation . . . . . . . . . . . . . . . . . 3-72Output Clamps . . . . . . . . . . . . . . . . . . . . . . . . 3-72Remote Low Clamping. . . . . . . . . . . . . . . . . . . . 3-73Valve Flow Characterization . . . . . . . . . . . . . . . . . 3-73Valve Dead-Band Compensation . . . . . . . . . . . . . . 3-75Tight Shutoff . . . . . . . . . . . . . . . . . . . . . . . . . 3-76Output Reverse . . . . . . . . . . . . . . . . . . . . . . . 3-77

Control Override . . . . . . . . . . . . . . . . . . . . . . . . . 3-77Recycle Valve Position Feedback . . . . . . . . . . . . . . . . 3-78

Air Miser. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-78

Maximum Flow . . . . . . . . . . . . . . . . . . . . . . . . . 3-79User Flow and Recycle Flow . . . . . . . . . . . . . . . . . . 3-79

Antichoke Control . . . . . . . . . . . . . . . . . . . . . . . . . . 3-81

Operating States . . . . . . . . . . . . . . . . . . . . . . . . . . 3-84

Transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-85Shutdown State . . . . . . . . . . . . . . . . . . . . . . . . . 3-86Idle State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-87Purge State . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-87Starting State . . . . . . . . . . . . . . . . . . . . . . . . . . 3-88Run State . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-89Manual State . . . . . . . . . . . . . . . . . . . . . . . . . . 3-89Remote Run State . . . . . . . . . . . . . . . . . . . . . . . . 3-91

Automatic Sequencing . . . . . . . . . . . . . . . . . . . . . . . 3-91


Contents

–4

Parameter Descriptions . . . . . . . . . . . . . . . . . . 4-1

Parameter Data Types . . . . . . . . . . . . . . . . . . . . . . . 4-1

Binary Parameters. . . . . . . . . . . . . . . . . . . . . . . . 4-2Integer Parameters . . . . . . . . . . . . . . . . . . . . . . . 4-2Floating-Point Parameters. . . . . . . . . . . . . . . . . . . . 4-2

Parameter Table . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Parameter Descriptions . . . . . . . . . . . . . . . . . . . . . . . 4-15

Operator Interface Module . . . . . . . . . . . . . . . . 5-1

Main Control Screen . . . . . . . . . . . . . . . . . . . . . . . . 5-1

Limiting Control Screens . . . . . . . . . . . . . . . . . . . . . . 5-4

Control Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

Operating Mode Selection . . . . . . . . . . . . . . . . . . . . . 5-9

Menu System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

Control Screen. . . . . . . . . . . . . . . . . . . . . . . . . . 5-11Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13OIM Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

Monitoring Application Status . . . . . . . . . . . . . . 6-1

Status Code Types . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

Monitoring Status Codes . . . . . . . . . . . . . . . . . . . . . . 6-1

History Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1Alarm Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Parameter Cross-References . . . . . . . . . . . . . . . A-1

April 20, 1998

Contents–5

FiguresFigure 2-1 Simplified Compressor Control Configuration . . . . . . 2-1

Figure 2-2 Performance and Resistance Curves . . . . . . . . . . 2-4

Figure 2-3 Operating Point of Compressor . . . . . . . . . . . . . 2-5

Figure 2-4 Surge Limit Line . . . . . . . . . . . . . . . . . . . . . 2-5

Figure 2-5 Surge Control Line and Safety Margin . . . . . . . . . . 2-6

Figure 3-1 Determining Surge and Operating Point Slopes . . . . . 3-1

Figure 3-2 Surge Limit Lines for a and Ne . . . . . . . . . . . . . . . . . . 3-2

Figure 3-3 Multidimensional Coordinate System . . . . . . . . . . 3-2

Figure 3-4 Control Lines with f4(Z4) = 1 . . . . . . . . . . . . . . . 3-8

Figure 3-5 Control Lines with f4(Z4) = 1/X . . . . . . . . . . . . . . 3-9

Figure 3-6 Calculating First-Stage Flow Rate from Second-Stage Discharge Flow Rate . . . . . . . . . . . 3-25

Figure 3-7 Calculating Second-Stage Flow Rate from First-Stage Suction Flow Rate . . . . . . . . . . . . . . 3-26

Figure 3-8 Antisurge Controller Functional Diagram. . . . . . . . . 3-35

Figure 3-9 Dead-Zone Error (e') Plotted as a Function of Actual Process Error . . . . . . . . . . . . . . . . . . . 3-39

Figure 3-10 Protecting a Multisection Compressor with aShared Recycle Valve . . . . . . . . . . . . . . . . . . 3-57

Figure 3-11 Load-Sharing Controller Configuration . . . . . . . . . . 3-65

Figure 3-12 Simplified Parallel Compressor Configuration . . . . . . 3-68

Figure 3-13 Cold Recycle Loop in a Parallel Network. . . . . . . . . 3-70

Figure 3-14 Valve Flow Characteristic Response. . . . . . . . . . . 3-75

Figure 3-15 Valve Dead-Band Compensation . . . . . . . . . . . . 3-76

Figure 3-16 User and Recycle Flows . . . . . . . . . . . . . . . . . 3-79

Figure 3-17 Simplified Antichoke Controller Configuration . . . . . . 3-81

Figure 3-18 Antichoke Control Lines . . . . . . . . . . . . . . . . . 3-82

Figure 3-19 Operating States and Transitions . . . . . . . . . . . . 3-84


Contents

–6

Figure 5-1 Antisurge Controller OIM . . . . . . . . . . . . . . . . . 5-2

Figure 5-2 Safety Margin and Surge Count Display . . . . . . . . . 5-4

Figure 5-3 Antisurge Controller Limiting Control Screens . . . . . . 5-4

Figure 5-4 Operating Mode Prompts. . . . . . . . . . . . . . . . . 5-9

Figure 5-5 Antisurge Main Menu. . . . . . . . . . . . . . . . . . . 5-10

Figure 5-6 Antisurge Variables Screen . . . . . . . . . . . . . . . 5-11

Figure 5-7 Antisurge Alarm Buffer . . . . . . . . . . . . . . . . . . 5-11

Figure 5-8 Antisurge History Buffer . . . . . . . . . . . . . . . . . 5-12

Figure 5-9 Application Options. . . . . . . . . . . . . . . . . . . . 5-13

Figure 5-10 Antisurge Configuration Menu . . . . . . . . . . . . . . 5-14

Figure 5-11 Sample Antisurge Subgroup and Parameter Lists . . . . 5-15

April 20, 1998

Contents–7

TablesTable 3-1 f1, f2, and f3 Characterizer Modes . . . . . . . . . . . . 3-4

Table 3-2 Numerator Modes (Y) . . . . . . . . . . . . . . . . . . 3-4

Table 3-3 Denominator Modes (X) . . . . . . . . . . . . . . . . . 3-5

Table 3-4 Valid Numerator and Denominator Combinations . . . . 3-5

Table 3-5 dPos Modes . . . . . . . . . . . . . . . . . . . . . . . 3-7

Table 3-6 f4 Characterizer Modes . . . . . . . . . . . . . . . . . 3-9

Table 3-7 Antisurge Controller Packet Variables . . . . . . . . . . 3-15

Table 3-8 Side Stream Comp Modes . . . . . . . . . . . . . . . . 3-22

Table 3-9 Span and Direction of PI Control Loops . . . . . . . . . 3-38

Table 3-10 Recycle Trip Status. . . . . . . . . . . . . . . . . . . . 3-47

Table 3-11 Example Safety On Accumulated Response. . . . . . . 3-49

Table 3-12 EAS Modes. . . . . . . . . . . . . . . . . . . . . . . . 3-51

Table 3-13 Limiting Control Loop Status . . . . . . . . . . . . . . . 3-52

Table 3-14 Valve Sharing Status . . . . . . . . . . . . . . . . . . . 3-59

Table 3-15 POC Status. . . . . . . . . . . . . . . . . . . . . . . . 3-61

Table 3-16 Valve Characterization Modes . . . . . . . . . . . . . . 3-74

Table 3-17 Signal Selection Logic for Antichoke Controller . . . . . 3-83

Table 3-18 Antisurge Controller Operating States . . . . . . . . . . 3-84

Table 3-19 Operating State Transitions . . . . . . . . . . . . . . . 3-85

Table 4-1 Antisurge Controller Parameters (Alphabetical) . . . . . 4-4

Table 5-1 Antisurge Controller LEDs . . . . . . . . . . . . . . . . 5-6

Table 6-1 Antisurge Controller Event Codes . . . . . . . . . . . . 6-2

Table 6-2 Antisurge Controller Alarm Codes . . . . . . . . . . . . 6-3

Table A-1 Parameter Cross-Reference . . . . . . . . . . . . . . . A-1

Table A-2 Parameters Listed by Group and Subgroup . . . . . . . A-9


Contents

–8

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April 20, 1998

Document Introduction

1-1

Chapter 1: Document Introduction

This document provides information on the configuration and operation of the Series 4 Antisurge Controller Application Function Module (AFM).

ProductsDiscussed in

This Document

This document deals only with Series 4 Antisurge Controller AFM, and discusses the various hardware and software modules that make up the AFM:

■ Input/Output Module

■ Antisurge Controller Application Software Package (ASP)

■ I/O Daughter Cards

Occasional references to other Series 4 products may be found in this manual as they relate to the Antisurge Controller.

For an overview of Series 4, please refer to UM4000, Series 4 System Overview. For additional information on the Series 4 AFM software, including fault tolerance, database organization, Modbus operation, and diagnostics, refer to UM4003, Series 4 Fault Tolerant Operating System.

DocumentContent

The contents of this document are described below, with additional detail shown in the table of contents.

Chapter 1 — Introduces this manual and includes a list of products and a list of related documents.

Chapter 2 — Provides an overview of the antisurge control function.

Chapter 3 — Contains theory of operation information for the Antisurge Controller, including a functional description.

Chapter 4 — Lists and describes the Antisurge Controller database parameters.

Chapter 5 — Contains information on configuring, operating, and monitoring the Antisurge Controller using an Operator Interface Module (OIM).

Chapter 6 — Contains information on monitoring the status of the Antisurge Controller application.


1-2


Appendix A — Contains cross-references between the Parameter Name and Symbol for each Antisurge Controller parameter.

A reader’s evaluation form is also included.

ConventionsUsed in This

Document

The following conventions are used throughout this document:

■ Acronyms — All acronyms are defined at their first occurrence in the document and may be defined at other places in the text.

■ Notes, Cautions, and Warnings — The following conventions are shown in the format in which they appear throughout the manual:

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

Caution: Cautions contain instructions which, if not followed, could lead to irreversible damage to equipment.

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

■ Revision Control — The document revision level follows the document number (in parenthesis) in the footer of odd-numbered pages. The document revision date is found in the footer of even-numbered pages.

■ Parameter Names — The italicized terms in this document are the names of the Antisurge Controller database parameters as they appear on the Operator Interface Module (OIM) displays. Analog and digital inputs and outputs are also italicized.

April 20, 1998


1-3

ReaderEvaluation

It is the goal of Compressor Controls Corporation to provide its customers with control systems which are unsurpassed in meeting their needs. It is equally important that the documentation which accompanies those control systems is also of the highest quality.

In the back of this manual you will find a reader’s evaluation form. We would appreciate any feedback you might have regarding this manual. If you have comments concerning a specific page, please return a copy of that page with your comments marked on it along with the evaluation form.


1-4



April 20, 1998

Antisurge Control Overview

2-1

Chapter 2: Antisurge Control Overview

Overview Every axial and centrifugal compressor will experience a damaging phenomenon known as surge when the flow through the compressor drops below a certain level. To prevent surge, this minimum flow level must be maintained by blowing-off a portion of the discharge to the atmosphere or recycling it back to the compressor inlet.

The recycle or blowoff flow is controlled by an antisurge valve, as shown in the simplified compressor control configuration in Figure 2-1. The throughput of the compressor is controlled by a performance control element, which can be a control valve (as shown), inlet guide vanes, or a rotational speed controller.

Figure 2-1 Simplified Compressor Control Configuration

The control system for the compressor must manipulate the performance control element and the antisurge valve to prevent surge-induced compressor damage or process upsets, while keeping a process variable (usually a pressure or flow rate) at a desired level. In a Series 4 Control System, these requirements are satisfied by a combination of Performance and Antisurge Controllers.

PIC: Performance Controller UIC: Antisurge Controller

UIC

FY

antisurgevalve

PIC

FY

controlvalve

Compressor

FTPTPTFT TT TT


2-2 Antisurge Control Overview

A single Antisurge Controller can be combined with a single Performance Controller to provide complete surge protection and capacity control for a single-section compressor operating with fixed or variable speed, geometry (guide vane angle), gas composition, and inlet conditions. More complex compressor systems can be controlled and protected by networks of Series 4 Antisurge, Performance, Fuel, Speed, and Extraction Controllers. To adequately protect a multisection compressor, each section should be protected by its own Antisurge Controller.

This manual discusses the configuration and operation of the Series 4 Antisurge Controller. The Series 4 Performance Controller is presented in UM4104, Using the Series 4 Performance Controller AFM.

An Antisurge Controller prevents surge in a dynamic compressor by controlling the blowoff or recycling of the discharge flow. Since increasing the blowoff or recycle flow affects other process conditions (such as lowering the discharge pressure), the Antisurge Controller can also be used to limit other conditions and variables.

Thus, the basic functions of an Antisurge Controller are:

■ To prevent surge-induced compressor damage and process upsets without sacrificing energy efficiency or system capacity.

■ To maintain selected process-limiting variables within safe or acceptable ranges.

In addition, an Antisurge Controller should minimize adverse interactions between its control actions and other control loops used with the compressor. It should also help to efficiently distribute the total load when the compressor is part of a series or parallel network.

Note: To avoid repeatedly using the term “recycle or blowoff,” the word “recycle” will hereafter be used in a generic sense (to imply either recycle or blowoff).

The antisurge valve is referred to throughout this manual as either the “antisurge valve” or the “recycle valve.”

April 20, 1998

Antisurge Control Overview 2-3

Principles ofSurge

Prevention

A dynamic compressor is essentially a device for adding energy to a flowing gas. Its performance can be illustrated by plotting the specific energy increase of the gas (commonly referred to as head) against the flow rate on a compressor map, as shown in Figure 2-2 on page 2-4. Compressor maps employ a variety of coordinate systems:

■ Head might be represented by a single variable (such as discharge pressure), a simple function (such as compression ratio), or a complex function of many variables (such as polytropic head).

■ Flow might be represented by anything from a simple measurement (such as pressure drop across an orifice plate in the suction or discharge line) to a complex function (such as pressure and temperature-compensated volumetric flow in suction).

■ Because the power consumption of the compressor is the product of the head, flow rate, and efficiency, it is also possible to plot head against power consumption or power against flow.

In most coordinate systems, the relationship between head and flow depends on one or more additional variables (such as suction temperature and pressure, gas composition, rotational speed, or inlet guide vane position). If all of these variables are held constant, the performance of the compressor can be represented by a single curve on the compressor map. As one of these variables is changed, a series of performance curves will be generated on the compressor map, each representing the performance of the compressor at a different value of that variable, as illustrated in blue in Figure 2-2.

For example, at a certain guide vane angle, the compressor will operate on performance curve AA. If the guide vane angle is changed to another value, the performance of the compressor would switch to curve BB.



Figure 2-2 Performance and Resistance Curves

Dynamic compressors are generally used to force a gas through some combination of inlet and outlet piping, valves, and process vessels which produce a certain amount of resistance. The head required to maintain various flows through this network resistance can be plotted as a series of resistance curves on the compressor map, as shown in black in Figure 2-2. Each curve represents the resistance, or load, for a certain network configuration.

For example, an increase in network resistance, such as the closing of a downstream valve, would cause the network resistance to jump from curve CC to curve DD.

At any given instant, the operation of a compressor can be represented by a single performance curve, and its load represented by a single resistance curve, as shown in Figure 2-3. Steady-state operation occurs when the actual discharge pressure and flow satisfy both curves.

Thus, the intersection of these performance and resistance curves represents the operating point of the compressor. The flow rate at this point is such that the energy added to the gas equals that required to overcome the network resistance. Any change in operating conditions will cause the flow, head, and compressor speed (if variable) to change until a new steady state is established.

Head

Flow

Constant

PerformanceCurves

A

A

B

BD

D

C

C

Resistance Curves

April 20, 1998


Figure 2-3 Operating Point of Compressor

For any given performance curve, the resistance curve and operating point will move up and to the left as the network resistance increases, since more pressure is required to sustain the same flow. Eventually, the compressor is unable to add enough energy to the gas to overcome the increased resistance, and a point of minimum stable flow and maximum head is reached. This point on the performance curve is called the surge limit point. The locus of the surge limit points for all performance curves defines the Surge Limit Line (SLL), as shown in Figure 2-4.

Figure 2-4 Surge Limit Line

Head

Flow

Operating Point

PerformanceCurves

ConstantResistance Curves

Head

Flow

Constant

PerformanceCurve

Surge Limit Line (SLL)

SurgeLimitPoint

ResistanceCurve



Attempting to operate to the left of the SLL will cause the compressor to surge. The flow rate and discharge pressure will then oscillate drastically until either the resistance decreases enough to restore a stable operating point, protective devices shut down the machine, or a catastrophic failure occurs.

The task of the Antisurge Controller is to keep the operating point to the right of the SLL. This is accomplished by opening the antisurge valve to recycle enough gas to maintain the required minimum flow rate.

In order to open the antisurge valve and increase the recycle flow before a compressor begins to surge, the control action of the Antisurge Controller must be initiated before the operating point reaches the SLL. For any given performance curve, the point at which the controller should start opening the antisurge valve is known as the surge control point. The locus of the surge control points for all performance curves defines the Surge Control Line (SCL), as shown in Figure 2-5. The distance between the SCL and SLL is called the Safety Margin. The antisurge valve should be opening whenever the operating point of the compressor is to the left of the SCL, within the Surge Control Zone shown in the figure.

Figure 2-5 Surge Control Line and Safety Margin

Head

Flow

Surge Limit Line (SLL)

Surge Control Line (SCL)

Safety Margin

SurgeControlZone

SurgeControlPoint

April 20, 1998


Because unnecessary recycling wastes energy, there is an economic incentive to accurately calculate how close the compressor is operating to the SLL and to minimize the Safety Margin needed to prevent surge.

Series 4 Antisurge Controllers are able to use the smallest possible Safety Margin by employing a combination of closed- and open-loop control responses that protect against surge-induced compressor damage and process upsets without sacrificing energy efficiency or system capacity. In addition to a flexible approach to accurately calculate proximity to surge and a unique combination of control responses, the Antisurge Controller also offers the following features:

■ multivariable surge calculations that are invariant to most changes in inlet conditions;

■ fallback strategies that can provide continued protection when the analog and serial communication inputs required for the chosen surge calculation fail;

■ limiting control loops that can increase the recycle rate as needed to maintain suction pressure (ps), discharge pressure (pd), or compression ratio (Rc);

■ a pressure override control response that can raise the recycle rate when needed to help limit a Performance Controller process variable;

■ Recycle Trip and Safety On functions which provide additional surge protection against large or fast disturbances;

■ a valve-sharing feature for protecting multisection compressors with a single, shared recycle valve;

■ load-sharing features for parallel or series compressor networks;

■ loop-decoupling to minimize adverse interactions between the various Series 4 Performance and Antisurge Controllers regulating a compressor; and

■ a variety of features (output reverse, output clamps, valve flow characterization, dead-band compensation, and tight shutoff) for matching the output signal to a specific recycle valve.




April 20, 1998

Theory of Operation 3-1

Chapter 3: Theory of Operation

Proximity toSurge

To prevent surge with a minimum of recycling, the Antisurge Controller must calculate an operating point position variable that always has the same, unique value when the compressor is at the surge limit. Ideally, this would be achieved by measuring performance in a two-dimensional coordinate system invariant to all process variables that affect proximity to surge. Then, the operating point position could be calculated as a function of both coordinates, and the value of that function at the surge limit would be a constant.

The Series 4 approach is to calculate the position of the operating point relative to the surge limit point as a ratio of the value of x on the Surge Limit Line (calculated as a function of y) to the value of x at the operating point, as shown in Figure 3-1.

Figure 3-1 Determining Surge and Operating Point Slopes

This ratio is used to obtain a proximity-to-surge variable, Ss:

where K is a scaling factor.

Therefore, the value of Ss is unity when the operating point of the compressor is on the Surge Limit Line; is less than one when the operating point is in the stable operating zone to the right of the SLL; and is greater than one when the compressor is in surge to the left of the SLL.

y

x

Operating PointSurge Limit Point(f(y), y) (x, y)

xf(y)

y

Surge Limit Line

Ss Kf y( )

x---------⋅=


3-2 Theory of Operation

If a two-dimensional coordinate system does not exist or is impractical to implement, a multidimensional surface is required to accurately represent the operation of the compressor. For example, if the equivalent speed (Ne) and guide vane angle (α) can vary, proximity to surge would be a function of one of those variables in addition to head and flow. This three-dimensional surface is usually represented as a series of surge lines on a two-dimensional map, as shown in Figure 3-2.

Figure 3-2 Surge Limit Lines for α and Ne

In such cases, if the value of the third coordinate is known, the position of the operating point relative to the SLL can be calculated as a function of the primary coordinates (x and y), and the third variable (z), as shown in Figure 3-3:

Figure 3-3 Multidimensional Coordinate System

RC

∆po/p

Surge Limit Lines for Constant

Surge Limit Lines for ConstantEquivalent Speeds (Ne)

Guide Vane Angles (α)

Ss K f⋅ z( ) f y( )x

---------⋅=

y

x

Operating PointSurge Limit Point

Surge Limit Lines

f(z) (x, y, z)

xf(y)

April 20, 1998


Numerator andDenominator

Modes

To accommodate this method of calculating proximity to surge, as well as other possible methods, the Series 4 Antisurge Controller allows the user to define the numerator (Y) and denominator (X) used in the calculation of Ss, and up to two surge limit characterizers:

where:

Ss = proximity-to-surge variable (Ss)

K = surge limit line slope coefficient (K)

f1 = surge limit characterizer (f1 Characterizer)

Z1 = argument (f1 Characterizer Mode)

f2 = surge limit characterizer (f2 Characterizer)


Y = coordinate variable of surge limit point(Numerator Mode)

X = coordinate variable of compressor operating point (Denominator Mode)

To reduce the effects of signal noise, the calculated value of Ss is passed through a first-order-lag software filter. The time constant for this filter is set using the S Tf parameter.

The f1 Characterizer Mode and f2 Characterizer Mode parameters are used to set the arguments for the f1 and f2 surge limit characterizing functions to one of the variables listed in Table 3-1.

Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=



Table 3-1 f1, f2, and f3 Characterizer Modes

The numerator and denominator used in the calculation of the proximity-to-surge variable are selected by setting the Numerator Mode and Denominator Mode parameters to the options listed in Table 3-2 and Table 3-3, respectively.

The Numerator and Denominator parameters give the current values of the numerator and denominator, and the K Prime parameter gives the value of the quantity [K · f1(Z1) · f2(Z2)].

Table 3-2 Numerator Modes (Y)

The f3 and f6 characterizers used in several of the numerator modes are configured using the f3 Characterizer and f6 Characterizer parameters. The argument (a) of the f3 characterizing function is selected using the f3 Characterizer Mode parameter, which assigns one of the variables in Table 3-1 to the function.

Variable Description

DISABLED 1 (linear) — function evaluates to one, so any value multiplied by that function does not change

SIGMA σ — polytropic head exponent

ALPHA α — guide vane angle

SPEED N — rotational speed

TS Ts — suction temperature

KW kW — drive power consumption

Name Numerator Mode (Y) Description

S CONTROL S control (see page 3-69)DPC Y = ∆pc pressure rise across the

compressor HP RED Y = hp reduced polytropic head

FUNC RC Y = f6(Rc) function of compression ratio

FUNC HP Y = f6[f3(a) · hp] selected function (a) and reduced polytropic head

FUNC HP TS Y = f6[f3(a) · Ts · hp] / Ts selected function (a), reduced polytropic head, and suction temp

April 20, 1998


Table 3-3 Denominator Modes (X)

For example, if the FUNC RC numerator and DPO DIV PS denominator modes are selected and the f1 and f2 characterizers are disabled, Ss would be calculated as:

Note: The Antisurge Controller can be configured to operate in a fallback mode if an input signal used in the chosen numerator or denominator modes fails. Refer to Fallback Strategies on page 3-27 for information.

Not all of the possible numerator and denominator mode combinations are valid in terms of surge control. Table 3-4 lists the valid and invalid combinations of Y and X.

Table 3-4 Valid Numerator and Denominator Combinations

Name Denominator Mode (X) Description

S CONTROL S control (see page 3-69)DPO X = dPo Calc calculated flow measurement

DPO DIV PS X = dPo Calc / ps reduced flow squared

DPO DIV PD X = dPo Calc / pd reduced flow in discharge squared

NO FLOW X = Ne2 = N

2 / Ts

when a flow measurement is not available, proximity to surge can be computed by replacing the flow parameter with the equivalent speed (Ne) squared.Note : This denominator mode is valid only when molecular weight is nearly constant.

Ss Kf6 Rc( )

dPo Calc ps⁄----------------------------------⋅=

Denominator Mode (X)

Numerator Mode (Y)

SCONTROL

DPO DPO DIVPS

NOFLOW

DPO DIVPD

S CONTROL VALID Invalid Invalid Invalid Invalid

DPC Invalid VALID Invalid Invalid Invalid

HP RED Invalid Invalid VALID VALID VALID

FUNC RC Invalid Invalid VALID VALID VALID

FUNC HP Invalid Invalid VALID VALID VALID

FUNC HP TS Invalid Invalid VALID Invalid Invalid



Caution: Configuring an invalid numerator (Y) and denominator (X) combination will result in an inaccurate measurement of proximity to surge, a surge event, or unnecessary recycling.

The Antisurge Controller does not prevent the configuration of an invalid combination or inform the user of an invalid combination.

The proximity-to-surge variable (Ss) is calculated as a function of reduced flow squared (qr

2), which requires a

measurement of the pressure drop across an orifice plate or venturi. This pressure drop measurement can be calculated using a combined flow measurement (dPo Used) from another location, such as downstream of an aftercooler. The method used to calculate this value, given by the dPo Calc parameter, is selected from the dPos Modes listed in Table 3-5.

Selecting the S CONTROL option for either the Numerator Mode, Denominator Mode, or dPos Mode configures the controller to provide S control for a parallel load-sharing network (see Cold Recycle (S) Control on page 3-69). It then selects the highest Ss reported by any of its companion hot-recycle controllers.

Note: When antichoke control is enabled, the numerator and denominator modes will be inverted. Refer to Antichoke Control on page 3-81 for more information.

April 20, 1998


Table 3-5 dPos Modes

Name dPo Calc = Description

S CONTROL S control (see page 3-69)SUCTION dPo Used when dPo Used is a suction flow

measurement, it can be used without any compensation being applied

DISCHARGE dPo Used · (Rc / T Ratio) when dPo Used is a measurement of discharge flow, dPo Calc can be calculated from dPo Used, the compression ratio, and the temperature ratio

AFTERCOOL dPo Used · Rc · (Ts / Tac) when dPo Used is the flow downstream of an aftercooler, dPo Calc can be calculated from dPo Used, the compression ratio, and the suction and aftercooler temperatures

RC CHAR dPo Used · f5(Rc) when dPo Used represents the flow downstream of an aftercooler, and the temperatures are not measured, dPo Calc can be calculated by multiplying dPo Used by a function of the compression ratio, where f5 is defined by f5 Characterizer

RC COMPdPo Used · Rc

1-σwhen dPo Used represents the flow downstream of an aftercooler and the temperatures are not measured, dPo Calc can be calculated from dPo Used and the Default Sigma (σ)

VLVE INLET dPo Used · (Pvi / Ps) when the flow is measured upstream of an inlet valve, dPo Calc can be calculated from dPo Used and the pressure on each side of the restriction

INTERSTAGE dPo Used · (Pis / Pd) · (Td / Tis)

when the flow is measured between compressor stages, dPo Calc can be calculated from dPo Used and the interstage pressure and temperature



Control Lines As discussed in Chapter 2, the Antisurge Controller bases proximity to surge on the distance between the operating point of the compressor and the Surge Limit Line (SLL). The controller also calculates a number of other control lines on the compressor map, as shown in Figure 3-4, which are used to determine its control responses and actions. These lines are determined relative to either the SLL or the Surge Control Line (SCL).

Figure 3-4 Control Lines with f4(Z4) = 1

Various control actions are triggered when the operating point of the compressor crosses the control lines:

■ The antisurge PI response increases the recycle rate when the operating point is to the left of the SCL, and reduces it when the point is to the right of the SCL.

■ The Recycle Trip response steps the antisurge valve open when the operating point is to the left of the Recycle Trip Line (RTL).

■ The Safety On response moves the SCL and RTL control lines to the right if the operating point moves to the left of the Safety On Line (SOL).

■ The tight shut-off response fully closes the antisurge valve when the operating point is to the right of the Tight Shutoff Line (TSL) and the control signal is at its minimum clamp.

Saf

ety

On

Line

x

Sur

ge L

imit

Line

y

Recyc

le Tr

ip L

ine

Surge Contro

l Line

Tight Shutoff L

ine

SOL SLL RTL SCL

TSL

April 20, 1998


Control LineCharacterizer

The control line characterizing function is used in the calculation of the Surge Control Line, Recycle Trip Line, Safety On Line, and Tight Shutoff Line. The argument (Z4) for the control line characterizer is specified by setting the f4 Characterizer Mode parameter to one of the variables listed in Table 3-6.

Table 3-6 f4 Characterizer Modes

For example, the ALPHA option would be appropriate if the surge limit point varies as a function of guide vane position only (if each performance curve is a line of constant vane angle). The f4 Characterizer parameter would then be used to define unique control line distances for each such curve.

The DISABLED option defines control lines that radiate from the origin of the map, as shown in Figure 3-4. If the f4 Characterizer Mode and the Ss denominator are the same, and the f4 Characterizer is defined as an inverse function, the control lines would appear as shown in Figure 3-5.

Figure 3-5 Control Lines with f4(Z4) = 1/X

Argument f4 Characterizer Mode

DISABLED 1 (Linear) — f4=1

DPO ∆po — compensated suction flow measurement (dPo Calc)

ALPHA α — guide vane angle process variable

SPEED N — rotational speed process variable

x

Sur

ge L

imit

Line

y SOL SLL RTL SCL TSL

Sur

ge C

ontro

l Lin

e

Saf

ety

On

Line

Tigh

t Shu

toff

Line

Rec

ycle

Trip

Lin

e

SO Distance

Safety Margin (b)

RT Distance

TSO Distance



Surge Limit Line As discussed in Principles of Surge Prevention on page 2-3, the Surge Limit Line (SLL) represents the limit at which a compressor will surge. When the operating point is to the right of the SLL the compressor will operate in a stable condition. When the operating point is to the left of the SLL, the compressor will surge.

The distance between the SLL and Surge Control Line (SCL) is determined by the calculated Safety Margin (b).

Safety Margin (b) The distance between the Surge Limit Line (SLL) and Surge Control Line (SCL), referred to as the Safety Margin (b), is the sum of the Safety On and derivative control responses:

b = CRSO + CRD = b1 + b2, n + b4 + CRD

where:

b = Safety Margin (b)

CRSO = Safety On control response (see page 3-47)

CRD = derivative control response (see page 3-41)

b1 = initial Safety On margin (SO Initial)

b2, n = accumulated Safety On bias(b2, n = b2, n-1 + SO Bias)

n = current number of surges (Surge Count)

b4 = additional Safety On margin (SO b4)

The controller calculates the position of the operating point line relative to the Surge Control Line using the proximity-to-surge variable, Ss, and the Safety Margin, b (see Operating Point on page 3-12).

Surge ControlLine

The Surge Control Line (SCL) defines the desired minimum distance between the operating point of the compressor and Surge Limit Line (SLL). The SCL is always to the right of the SLL, as shown in Figure 3-5. The distance between the Surge Limit Line (SLL) and Surge Control Line (SCL) is determined by the value of the Safety Margin (b), discussed in the previous section.

The PI response of the controller will increase the recycle rate when the operating point is to the left of the SCL and reduce it when the point is to the right of the SCL (see Antisurge PI Response on page 3-40).

April 20, 1998


Safety On Line The Safety On Line (SOL) defines an operating limit beyond which the compressor is assumed to be surging. The SOL is always on or to the left of the Surge Limit Line (SLL), as shown in Figure 3-5.

The distance between the SOL and SLL, referred to as the Safety On Distance, is determined by applying the f4 control line characterizing function to the specified value of the SO Distance parameter:

SO Distance · f4(Z4)

When the operating point of the compressor moves to the left of the Safety On Line, the Safety On response will increment the surge count and increase the Safety Margin (b) to move the Surge Control Line (SCL) and Recycle Trip Line (RTL) to the right (see Safety On Response on page 3-47).

Recycle Trip Line The Recycle Trip Line (RTL) defines an operating limit beyond which the Recycle Trip response will incrementally step the recycle valve open. The position of the RTL is defined relative to the Surge Control Line (SCL), as shown in Figure 3-5.

The distance between the RTL and SCL, referred to as the Recycle Trip Distance, is determined by applying the f4 control line characterizing function to the specified value of the RT Distance parameter:

RT Distance · f4(Z4)

When the operating point of the compressor moves to the left of the Recycle Trip Line, the Recycle Trip response will step the recycle valve open (see Recycle Trip Response on page 3-42).

Tight ShutoffLine

The Tight Shutoff Line (TSL) defines the minimum deviation (Deviation) between the operating point and the SCL above which the Tight Shutoff response will reduce the value of the Display Output parameter to zero (see Tight Shutoff on page 3-76). The TSL is always to the right of the SCL, as shown in Figure 3-5.

The distance between the TSL and SCL, referred to as the Tight Shutoff Distance, is determined by applying the f4 control line characterizing function to the specified value of the Tight Shut Off Distance parameter:

Tight Shut Off Distance · f4(Z4)



When the operating point of the compressor moves to the right of the Tight Shutoff Line (Deviation > Tight Shut Off Distance · f4), and the intended valve position is at the low clamp, the controller will force the Display Output to zero.

Operating Point The position of the operating point relative to the Surge Control Line (SCL) is calculated using the value of Ss and the Safety Margin.

S = Ss + Safety Margin = Ss + b · f4(Z4)

where:

S = position of operating point relative to SCL (S)


b = Safety Margin (b)

f4 = control line characterizer (f4 Characterizer)


The S Calc Updated parameter is incremented every time a parameter which affects the calculation of the S variable is changed using WOIS Configurator.

The Deviation parameter, which is used primarily for display purposes, is calculated by complementing S:

Deviation = 1 – S = 1 – [Ss + b · f4(Z4)]

Thus, the Deviation will decrease as the operating point moves to the left toward the SCL; will have a value of zero at the SCL; and will be negative when the operating point is to the left of the SCL. The antisurge PI response increases the recycle rate when Deviation < 0, and reduces it when Deviation > 0.

April 20, 1998


ControllerInputs and

Outputs

A number of inputs and outputs are associated with each Series 4 controller. Inputs allow the controller to obtain process data and control information, while outputs allow the controller to manipulate or provide status information to external devices.

There are two basic types of inputs and outputs:

■ Numeric inputs and outputs usually have floating point values that vary continuously from 0 to 100 percent of its span. They are normally associated with the voltage, current, or frequency of an electrical signal. Numeric inputs and outputs are often referred to as analog inputs and outputs even though, technically speaking, analog inputs and outputs are electrical signals.

■ Binary inputs and outputs vary between two states (which can be referred to as 1 and 0, On and Off, True and False, or Set and Cleared). Binary inputs and outputs are commonly referred to as digital or discrete inputs and outputs.

Physical I/O channels are normally used for most process inputs and control outputs. However, controllers can access each other’s database parameters and can also exchange information with one another using data packets. Finally, Modbus serial communications can be used to read some outputs and to set some otherwise unassigned inputs (see publication DS 4102/M, Series 4 Antisurge Controller Modbus Data Sheet).

A more detailed explanation of controller input and outputs can be found in publication UM4003, Series 4 Fault Tolerant Operating System.

Input/OutputConfiguration

Logical TO Physical (LTOP) arrays are used to assign parameter or data packet sources to the controller’s inputs. They are also used to assign parameter destinations to the controller’s outputs. (A predefined set of output values is placed in data packets, so they do not need to be configured.)

Each element in an LTOP array corresponds to a controller input or output. A parameter address or data packet reference is entered into each element in the array, thereby creating a link between each input or output and its data source or destination.



There are two LTOP input arrays used in the Antisurge Controller:

■ The Analog Inputs LTOP array assigns sources to analog inputs.

■ The Digital Inputs (2) LTOP arrays assign sources to digital inputs.

There are two LTOP output arrays used in the Antisurge Controller:

■ The Analog Outputs array assigns destinations to analog outputs.

■ The Digital Outputs arrays assign destinations to digital outputs.

Warning! Each output can be assigned to any nonprotected parameter of the same data type. This can produce unpredictable results, since the parameter to which the output is assigned may be calculated by another function as well, causing the two value to overwrite each other.

Input/OutputFault Detection

Failures of input and output signals at the hardware level are detected by the Fault Tolerant Operating System (FTOS). If an input or output error condition exists, a failure flag will be set in the FTOS database, and an alarm for the failed input or output will be recorded in the FTOS alarm and history buffers. Refer to UM4003, Series 4 Fault Tolerant Operating System, for more information.

The Antisurge Controller monitors the FTOS failure flags for the analog input channels. If the analog input assigned to one of these channels fails, an alarm will be recorded in the Antisurge Controller alarm and history buffers (see Chapter 6). Likewise, the analog outputs are also monitored by the controller, and an alarm will be recorded if an analog output fails.

The FT Alarm Level parameter is used to define the action that should be taken by the FTOS for most critical I/O failures.

April 20, 1998


Packet Data Certain Antisurge Controller database parameters can be accessed by other controllers in the system through the use of data packets. Inputs from and outputs to other Series 4 controllers are often used in applications such as load-sharing compressors and other systems where a high degree of interaction between controllers exists. Table 3-7 lists the controller data packet variables which can be exchanged with other Series 4 controllers.

Table 3-7 Antisurge Controller Packet Variables

Parameter Name Data Type

CV FloatCV Total FloatFlow FloatS FloatR FloatQ Max FloatQ User Float

Q Recycle FloatdPo Comp FloatSelected P FloatSelected I FloatStatus Integer

LD Valid BitRB Valid BitSO BitRunning Bitspare Float, Integer, or Bitspare Float, Integer, or Bitspare Float, Integer, or Bitspare Float, Integer, or Bitspare Float, Integer, or Bitspare Float, Integer, or Bitspare Float, Integer, or Bit



ProcessVariables

Many of the process variables in the Antisurge Controller represent compressor operating conditions, which generally fall into the following categories:

■ Measured process variables are process conditions usually obtained from analog inputs (for example, suction pressure).

■ Calculated process variables are process conditions computed from the measured variables, usually because they cannot be directly measured (for example, reduced polytropic head).

MeasuredVariables

The Antisurge Controller can measure the following compressor operating conditions. The parameters within the Antisurge Controller which correspond to the measured variables are shown in italics.

■ The main flow measurement (dPo1) represents the pressure drop across a suction or discharge orifice plate.

■ The dPo2 flow measurement is a redundant input for dPo1.

■ The sidestream flow measurement (dPo Side) represents the pressure drop across a sidestream orifice plate.

■ The suction pressure (Ps) represents the absolute pressure at the compressor inlet. If no source is defined, Ps is calculated as Pd – dPc.

■ The discharge pressure (Pd) represents the absolute pressure at the compressor outlet. If no source is defined, Pd is calculated as dPc + Ps.

■ The pressure change (dPc) represents the increase in pressure across the compressor. If this value is needed but no source is defined, dPc is calculated as Pd – Ps.

■ The inlet valve pressure (Pvi) represents the absolute pressure upstream of an inlet control valve.

■ The interstage pressure (Pis) represents the absolute pressure between compressor stages.

■ The suction temperature (Ts) represents the absolute temperature at the compressor inlet. If no source is defined, Ts is calculated as Td – dTc.

■ The discharge temperature (Td) represents the absolute temperature at the compressor outlet. If no source is defined, Td is calculated as dTc + Ts.

April 20, 1998


■ The temperature rise (dTc) represents the change in temperature across the compressor. If this value is needed but no source is defined, dTc is calculated as Td – Ts.

■ The aftercooler temperature (Tac) represents the absolute temperature downstream of an aftercooler.

■ The interstage temperature (Tis) represents the absolute temperature between compressor stages.

■ The rotational speed (N) represents the rotational speed of the compressor.

■ The guide vane angle (Alpha) represents the angular opening of the inlet guide vanes.

■ The drive power measurement (kW) represents the rate at which energy is being supplied to the compressor.

■ The ambient air temperature (T Air) input is currently not used in the controller.

■ The cooling water temperature (T CW) input is currently not used in the controller.

Most of these measurements are obtained by scaling analog inputs, however, some can be provided by specified companion controllers or by serial communications.

RedundantSignal Selection

The values of some measured process variables can be selected from two redundant inputs. This option is currently provided for the main flow measurements (dPo1 and dPo2), the sidestream flow measurement (dPo Side), the suction pressure and temperature (Ps and Ts), and the discharge pressure and temperature (Pd and Td).

The Antisurge Controller will set the value of the dPo Used parameter equal to the lower of the dPo1 and dPo2 parameters. The value of the dPo Select parameter indicates which of the two signals is being used. If the difference between these two signals exceeds the value specified by the dPo Differential Threshold parameter, a “dPo Differential” alarm will be generated, and the dPo Dev parameter will be set to On.

For the discharge pressure and temperature, the controller selects the higher signal from up to two redundant transmitters for each input.

For the suction pressure, the controller calculates Ss for each redundant transmitter signal and selects the suction pressure input which gives the higher Ss value. The Rc, Sigma, and Hp are assigned according to the selected Ps. For limiting



control, the controller selects the lowest suction pressure and uses it as the suction pressure limit process variable (Ps Limit PV).

For the suction temperature and the sidestream flow, the controller selects the lower signal from the two redundant transmitters for each input.

Process VariableScaling

Process variables obtained from numeric inputs are scaled by applying their span and offset parameters. For example, the scaling for the speed (N) is calculated using the N Offset and N Span parameters:

N = (speed input · N Span) + N Offset

Limiting control set points are scaled using their process variable spans and offsets.

These spans and offsets must be assigned values that would convert a parameter value from the scale of its source to the selected display units:

■ The Pressure EU and Pressure2 EU parameters are used to select the pressure display units.

■ The Pressure Rate EU parameter is used to select the pressure rate display units.

■ The Temperature EU and Temperature2 EU parameters are used to select the temperature display units.

■ The Power EU parameter is used to select the power display units.

■ The dPressure EU and dPressure2 EU parameters are used to select the pressure display units.

■ The dPressure Rate EU parameter is used to select the pressure rate display units.

■ The Suction Pressure EU and Suction Pressure2 EU parameters are used to select the suction pressure display units.

The operator interface device then converts the span and offset to the values needed to scale the input to its internal SI units.

Each parameter’s span and offset are also used to scale the value of its Modbus register (if applicable). For example, the value of the suction pressure Modbus register is normalized using the Ps Offset and Ps Span parameters:

April 20, 1998


Variables received by packet communications are assumed to be already scaled to the internal SI units, therefore their spans and offsets are used only to scale their Modbus registers. For example, if the rotational speed is obtained by packet communication, the speed parameter (N) is calculated by multiplying the speed signal by the specified Gear Ratio:

N = Npacket · Gear Ratio

The N Span and N Offset are then used to normalize the value reported by the Modbus N register:

Any numeric input obtained from a system analog input parameter is normalized. Thus, its span and offset must be equated to the transmitter’s minimum and maximum signals scaled to the corresponding engineering units:

Offset = minimum PV

Span = maximum PV – Offset

For example, if psig has been selected as the pressure unit for a 0 to 500 psig current-loop pressure transmitter, Ps Offset should be set to zero and Ps Span should be set to 500. The displayed suction pressure would then vary from 0 to 500 as the input varied from 4 to 20 mA, while the Modbus register would range from zero to 4095.

Normalized values (which vary from zero to one or from negative one to one) are displayed as percentages. For example, if the internal value of the Display Output parameter is 0.531, an OIM will display it as 53.1%.

PsModbus 4095Ps Ps Offset–

Ps Span--------------------------------------

⋅=

NModbus 4095N N Offset–

N Span--------------------------------

⋅=



CalculatedVariables

The Antisurge Controller calculates as many of the following parameters as are required by the selected surge protection and load-sharing algorithms:

■ Rc — compression ratio

■ T Ratio — temperature ratio

■ Sigma — polytropic head exponent

■ Hp — reduced polytropic head

■ dPo Calc — compensated flow measurement used in the calculation of the Surge Control Line (SCL).

■ dPo Comp — flow measurement reported to sidestream controller for flow calculation of sidestream stage

■ dPo Used — selected flow measurement

■ R — mass flow rate squared (for series load sharing)

■ Ss — proximity-to-surge variable

■ S — S variable

CompressionRatio

The compression ratio is the ratio of the discharge and suction pressures:

where:

Rc = compression ratio (Rc)

pd = discharge pressure (Pd)

ps = suction pressure (Ps)

TemperatureRatio

The temperature ratio is the ratio of the discharge and suction temperatures:

where:

TR = temperature ratio (T Ratio)

Td = discharge temperature (Td)

Ts = suction temperature (Ts)

Rc

pd

ps------=

TR

Td

Ts------=

April 20, 1998


Polytropic HeadExponent

The Antisurge Controller uses the following equation (which can be derived from thermodynamic principles) to calculate the polytropic head exponent (Sigma):

where:

σ = polytropic head exponent (Sigma)


Ts = suction temperature (Ts)


ps = suction pressure (Ps)

Because pressure measurements are more responsive than temperature measurements, the calculated value of Sigma is passed through a first-order-lag software filter. The time constant for this filter is set using the Sigma Tf parameter.

Since temperature measurements lag significantly during a start-up, the controller will initialize Sigma to the value specified by the Default Sigma parameter when the compressor is started. The sigma filter will then effect a gradual transition to the calculated Sigma value.

ReducedPolytropic Head

As explained in Proximity to Surge on page 3-1, reduced polytropic head (Hp) is defined and calculated as:

where:

hp = reduced polytropic head (Hp)

Rc = compression ratio (Rc)

σ = polytropic head exponent (Sigma)

Suction Flow When the dPos Mode parameter is set to SUCTION (see Table 3-5 on page 3-7), dPo Calc is set to the value of dPo Used, which is a suction flow measurement.

σTd Ts⁄( )log

pd ps⁄( )log------------------------------=

hp

Rcσ 1–

σ----------------=



Reported Flow Each Antisurge Controller calculates a reported flow measurement included in the data packet it sends to its companion controllers. This value, given by the dPo Comp parameter, is calculated from dPo Calc based on the Side Stream Comp Mode selected from Table 3-8.

Table 3-8 Side Stream Comp Modes

Mass FlowRate

The mass flow rate (Flow) is calculated from specified flow, temperature, and pressure measurements, all of which must correspond to the same physical location (generally an orifice plate installed in the suction or discharge line):

where:

Flow = mass flow rate (Flow)

CF = mass flow scaling coefficient (Flow Coefficient)

∆po = flow measurement (Flow Channel)

po = pressure (Pressure Channel)

To = temperature (Temperature Channel)

Name dPo Comp = Description dPo Measurement

DPOS dPo Calc when the companion controller needs the suction flow measurement (dPos) from the compressor, dPo Calc can be reported without any compensation being applied

Downstream

FUNCT RC dPo Calc · f5(Rc) when the companion controller needs the discharge flow measurement from the compressor, dPo Comp can be calculated by applying a characterizer to dPo Calc, where f5 is defined by f5 Characterizer

Upstream

RC SIGMAdPo Calc · Rc

σ-1when the companion controller needs the discharge flow measurement (dPod) from the compressor, dPo Comp can be calculated from compression ratio and sigma (σ)

Upstream

PRESS TEMP dPo Calc · (T Ratio / Rc) when the companion controller needs the discharge flow measurement (dPod) from the compressor, and the suction and discharge temperatures are measured, dPod can be calculated from the compression and temperature ratios

Upstream

Flow CF

∆po po⋅To

--------------------=

April 20, 1998


Note: When specifying the value of CF (Flow Coefficient), the user must calculate a value consistent with the pressure and temperature units used in the equation.

The flow measurement (∆po) is selected by setting the Flow Channel parameter to either DPO or DPO SIDE, whichever corresponds to the temperature and pressure where the flow is measured.

Similarly, the pressure (po) is selected by setting the Pressure Channel parameter to the suction pressure (Ps), discharge pressure (Pd), inlet valve pressure (Pvi), or interstage pressure (Pis).

Finally, the temperature (To) is selected by setting the Temperature Channel parameter to the suction temperature (Ts), discharge temperature (Td), aftercooler temperature (Tac), or interstage temperature (Tis).

The Flow Span and Flow Offset are used to calculate the normalized mass flow rate reported by the Modbus register:

Because this flow rate will vary from zero to some maximum value, its span should be set equal to the maximum flow and its offset should be set to zero.

Series load-sharing applications use a load-balancing variable (R) based on the total mass flow rate squared (see Load-Balancing Response on page 3-67). This parameter is calculated by each Antisurge Controller, and is included in the data packets they each send to their companion Load Sharing Performance Controllers.

WnModbus 4095

Flow Flow Offset–Flow Span

-------------------------------------------------- ⋅=



where:

R = mass flow rate squared (R)

W2

= mass flow rate squared

β5 = R scaling coefficient (Beta 5)




MultisectionCompressorFlow Rates

The flow through a multisection compressor is often measured only for the first or last section. If the Antisurge Controllers for the other compressor sections require flow measurements, they must be calculated from the flow through the preceding or following stage. Series 4 Antisurge Controllers can share flow measurements and calculate their total flow rates by combining their main and sidestream flows in the following mass balance equation:

where:

∆po = combined flow measurement (dPo Used)

∆po, 1 = main flow measurement(dPo Comp of sender)

∆po, 2 = sidestream flow measurement (dPo Side)

C1 = Flow Sidestream Coefficient 1



For the two-stage compressor shown in Figure 3-6, the sidestream and discharge flow rates are measured.

R W2 β5∆po po⋅

To--------------------

= =

po∆ C1 po 1,∆⋅( ) C2 po 2,∆⋅( ) C3 po 1,∆ po 2,∆⋅+ +=

April 20, 1998


Figure 3-6 Calculating First-Stage Flow Rate from Second-Stage Discharge Flow Rate

To determine the flow rate through the first section, the following steps are required:

Step 1: The dPos Mode parameter for the second-stage controller (UIC2) is set to any dPos Mode which will compensate the measured discharge flow to suction (DISCHARGE or AFTERCOOL):

dPo Calc = dPo Used · (Rc / T Ratio)

Step 2: The Side Stream Comp Mode parameter for UIC2 is set to DPOS because it is already compensated to suction, therefore:

dPo Comp = dPo Calc

Step 3: The Side Stream Companion parameter for UIC1 is set to the address of UIC2 to get the value of dPo Comp from UIC2.

Step 4: The value of dPo Comp from UIC2 is used with the measured sidestream value (dPo Side) in the mass balance equation (on page 3-24) to calculate dPo Used for UIC1.

dPo CompUIC

1UIC

2

FT1PT FT2PT PT

UIC1:

dPo Comp from UIC2dPo Side = FT1dPo Used = calculated from mass balance equation

UIC2:

dPo Used = FT2dPo Calc = dPo Used · (Rc / T Ratio)

dPo Comp = dPo Calc

Side Steam Companion = UIC2 address

dPos Mode = DISCHARGE

Side Steam Comp Mode = DPOS

dPo Used (UIC1)



Step 5: Ss for UIC1 is calculated by setting up the appropriate dPos Mode, Numerator Mode, and Denominator Modes. The value of dPo Used in the chosen dPos Mode equation is the value calculated in Step 4.

For the two-stage compressor shown in Figure 3-7, the suction and sidestream flow rates are measured.

Figure 3-7 Calculating Second-Stage Flow Rate from First-Stage Suction Flow Rate

To determine the flow rate through the second section, the following steps are required:

Step 1: The Side Stream Comp Mode parameter for the first-stage controller (UIC1) is set to FUNCT RC, RC SIGMA, or PRESS TEMP to compensate the measured suction flow to discharge. For FUNCT RC,

dPo Comp = dPo Calc · f5(Rc)

dPo CompUIC

1UIC

2

FT2PT PT PTFT1

UIC2:

dPo Comp = dPo Comp from UIC1dPo Side = FT2dPo Used = calculated from mass balance equation

UIC1:

dPo Used = FT1dPos Mode = 1 (dPo Calc = dPo Used)dPo Comp = dPo Calc · f5(Rc)

Side Stream Comp Mode = FUNCT RC

Side Stream Comp Mode = UIC1 address

April 20, 1998


Step 2: The Side Stream Companion parameter for UIC2 is set to the address of UIC1 to get the value of dPo Comp from UIC1.

Step 3: The value of dPo Comp from UIC1 is used with the measured sidestream value (dPo Side) in the mass balance equation (on page 3-24) to calculate dPo Used for UIC2.

Step 4: Ss for UIC2 is calculated by setting up the appropriate dPos Mode, Numerator Mode, and Denominator Modes. The value of dPo Used in the chosen dPos Mode equation is the value calculated in Step 3.

FallbackStrategies

The Series 4 Antisurge Controller offers a variety of proximity-to-surge calculations to tailor it to specific applications. When the input signals required for a particular application are lost due to communication errors or transmitter failures, it is feasible to provide continued surge protection by substituting a constant default value for a failed input.

The Antisurge Controller offers a number of fallback strategies which allow continuous surge protection in the event of failed inputs. These fallback modes are used when input or communication failures prevent the controller from calculating the proximity-to-surge variable, Ss.

Some of the Antisurge Controller fallback strategies are continuously enabled and will be triggered whenever certain conditions are detected. Others must be configured and enabled by the user. The specific fallback modes used in the Antisurge Controller depend on which fallback strategies are enabled and which inputs have failed.

Whenever a fallback mode is active, the Fallback parameter will be set to On and the fallback LED on the Operator Interface Module (OIM) will be illuminated.

Adjacent FlowFallback

When the Default Adjacent Flow Enable parameter is set to On, an Antisurge Controller that is unable to obtain a valid dpo value from a designated sidestream companion controller will use the value specified by the Default Adjacent Flow Rate parameter, in place of dPo Comp from the sidestream companion controller.



CompressionRatio Fallback

When the Default Rc Enable parameter is set to On, the controller will use the value of the Default Rc parameter in place of Rc when the discharge pressure input fails.

Inlet ValveFallback

When the dPos Mode parameter is set to VLVE INLET, the suction flow measurement is compensated for a flow restriction. If the required pressure measurement (Pvi) fails, the compensation will be suspended (dPos Mode will be set to SUCTION). This fallback will not compromise surge protection since the uncompensated flow rate in such applications will always be less than the true flow rate.

The inlet valve fallback is continuously enabled within the Antisurge Controller.

Limiting ControlFallbacks

Limiting control of the minimum suction pressure or maximum discharge pressure will be suspended if a required analog input fails. Also, limiting control of the compression ratio (Rc) will be suspended if the suction pressure (Ps) or discharge pressure (Pd) inputs fail.

These limiting control fallbacks are continuously enabled within the Antisurge Controller.

Minimum FlowFallback

When the Minimum Flow Control Enable parameter is set to On, various input failures will cause the controller to calculate Ss as the ratio of dPosmin and the suction flow measurement:

where:


dPosmin = minimum flow set point (Minimum Flow Set Point)

dPosuction = suction flow measurement (dPo Used)

Note: This fallback does not use the Surge Limit Line coefficient and its characterizers (K, f1, and f2).

Ss

dPosmin

dPosuction-------------------------=

April 20, 1998


A failure of the suction or discharge pressure input when the DPO DIV PS or DPO DIV PD denominator mode is being used will cause a minimum flow fallback.

The controller will also go to the minimum flow fallback strategy in response to various input failures if the following input fallback strategies (discussed on the following pages) are disabled:

■ Polytropic Head Fallback

■ Sigma Fallback

■ Discharge Pressure Fallback

■ Suction Pressure Fallback

■ Discharge and Suction Temperature Fallback

If the minimum flow fallback is disabled (Minimum Flow Control Enable is Off), any condition that would normally trigger it will cause the controller to fall back to Run Freeze operation.

Polytropic HeadFallback

When the Temperature Based Hp Enable and Default Sigma Enable parameters are set to On, and the discharge pressure input fails, the controller will calculate hp using the temperature ratio and the value of the Default Sigma parameter:

where:

hp = reduced polytropic head (Hp)

TR = temperature ratio (T Ratio)

σdefault = default polytropic head exponent (Default Sigma)

This thermodynamic relationship demonstrates that reduced polytropic head can be calculated from σ and either the compression ratio or temperature ratio. Because pressure measurements usually react more quickly than temperature measurements, the compression ratio calculation is preferred and the temperature ratio method is provided as a fallback.

If the Default Sigma Enable parameter is not enabled, the controller will go to the minimum flow fallback strategy.

hp

TR 1–( )σdefault

---------------------=



Run FreezeFallback

The Run Freeze fallback strategy is continuously enabled within the Antisurge Controller. The following conditions will cause the controller to enter this fallback:

■ a failure in a dPo signal;

■ the failure of dPo Side on a sidestream controller;

■ the failure of Pis or Tis on an interstage controller;

■ a valve-sharing secondary controller enters a run freeze fallback; or

■ the minimum flow fallback is called but is not enabled.

This fallback forces the controller into a suspended RUN mode and initializes the Output parameter to the higher of the Default Output parameter or a filtered output value which is relatively unaffected by any transients that may have occurred as a result of input failures. Setting the Default Output parameter to zero will cause the controller to select the filtered output.

If the Manual Fallback Enable parameter is set to On when the controller enters a run freeze fallback, the controller will go to the Manual state. The user can then manually adjust the Output parameter to any desired value (see Manual State on page 3-89).

The S Failure parameter will be set to On when the Antisurge Controller enters the run freeze fallback.

Sigma Fallback When the Default Sigma Enable parameter is set to On, the controller will use the value of the Default Sigma parameter in place of Sigma if the discharge pressure, discharge temperature, or suction temperature input fails.

If the Default Sigma Enable parameter is not enabled, the controller will go to the minimum flow fallback strategy.

Valve-SharingFallback

When the Alternate K Enable parameter is set to On, the controller will use the value of the Alternate K parameter instead of the specified slope coefficient (K) to calculate Ss if the controller fails to receive valid data from any one or more of its designated valve-sharing companion controllers.

Giving the Alternate K parameter a larger value than K will then yield a larger value for Ss, thus effectively increasing the Safety Margin.

If the valve-sharing fallback is disabled, the Antisurge Controller will continue to use the specified K value.

April 20, 1998


AftercoolerTemperature

Failure

When the dPos Mode parameter is set to AFTERCOOL, the calculated flow measurement (dPo Calc) is compensated for the flow measurement downstream of an aftercooler. If the aftercooler temperature (Tac) signal fails, the discharge temperature (Td) will be used in place of Tac (dPos Mode will be set to DISCHARGE). Because this fallback underestimates the flow rate, it provides uncompromised surge protection by increasing the recycle rate beyond what is needed.

Note: The aftercooler temperature fallback requires that any application using the AFTERCOOL dPos Mode must measure Td as well as Tac.

The aftercooler temperature fallback is continuously enabled within the Antisurge Controller.

DischargePressure Failure

A valid discharge pressure (Pd) is needed to calculate the compression ratio (Rc), which is used to compute the polytropic head exponent (Sigma) and reduced polytropic head (Hp). Consequently, failure of the Pd input will trigger the following fallback modes:

■ If the FUNCT RC Numerator Mode is selected, the controller will calculate Ss using the value of the Default Rc parameter if the compression ratio fallback is enabled (Default Rc Enable is On). Otherwise, it will fall back to minimum flow control.

■ If a Numerator Mode requiring Hp is selected, the controller will calculate Ss using the values of the T Ratio and Default Sigma parameters, provided that both the polytropic head and sigma fallbacks are enabled, and both temperatures are valid.

If the sigma fallback is disabled, the controller will fall back to minimum flow control.

If the polytropic head fallback is disabled or the T Ratio is invalid, the controller will calculate Ss using the values of the Default Rc and Default Sigma parameters, provided both the compression ratio and sigma fallbacks are enabled. Otherwise, it will fall back to minimum flow control.

Discharge pressure and compression ratio limiting are also suspended whenever the Pd input fails.



Discharge andSuction

TemperatureFailure

Valid suction and discharge temperatures (Ts and Td) are needed to calculate the temperature ratio (T Ratio), which is used to calculate the polytropic head exponent (Sigma) and reduced polytropic head (Hp). Thus, failure of the Ts or Td input will trigger the following fallback actions:

■ If a Numerator Mode that requires reduced polytropic head (Hp) is selected, and the Default Sigma Enable parameter is set to On, the value of the Default Sigma parameter will be used in the calculation of reduced polytropic head, and as the argument of any functions of Sigma. If Default Sigma Enable is Off, the controller will go to the minimum flow fallback strategy.

■ The RC COMP dPos Mode will be used in place of the DISCHARGE or AFTERCOOL dPos Mode calculations.

The dPos Modes are given in Table 3-5 on page 3-7.

dPo Failure Most proximity-to-surge calculations require a measurement of the total flow through the compressor. Failure of the flow measurement will automatically trigger a run freeze fallback (see page 3-30).

Note: If the NO FLOW Denominator Mode is selected, failure of any required input will trigger the run freeze fallback.

Speed Failure When the Default Speed Enable parameter is set to On, a failure of the speed input (N) will cause the controller to use the value of the Default Speed parameter in place of N. The N Fail digital input is On when there is a failure of the speed input.

If this parameter is Off when the speed input fails, the controller will continue to calculate S using the invalid speed.

Suction PressureFailure

When the Default Ps Enable parameter is set to On, the controller will use the value of the Default Ps parameter in place of a failed suction pressure (Ps) input.

Suction pressure and compression ratio limiting are also suspended when the Ps input fails.

If the default suction pressure fallback is disabled (Default Ps Enable is Off) and the DPOS DIV PS Denominator Mode is selected, a suction pressure failure would preclude the calculation of Ss and trigger the minimum flow fallback.

April 20, 1998


If any dPos Mode other than DPO DIV PS is selected, suction pressure would still be needed to calculate the compression ratio (Rc), which is used to compute the polytropic head exponent (Sigma) and reduced polytropic head (Hp). Failure of the Ps input would then be handled as a discharge pressure failure (see page 3-31).

Guide VaneAngle Failure

When the Default Alpha Enable parameter is set to On, a failure of the guide vane input (Alpha) will cause the value of the Default Alpha parameter to be used in any calculation that would normally use Alpha.

If the vane angle fallback is disabled (Default Alpha Enable is Off), the controller will continue to calculate S using the invalid vane angle.



AntisurgeControllerFunctions

A single antisurge valve is often the best available control element for more than one control objective. 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 discharge pressure. In other cases, only one recycle valve may be installed on a multicase or compound compressor, so the recycle rate must be kept high enough to prevent surge from developing in any section.

Consequently, the overall control variable (CV Total) for the Antisurge Controller, which represent recycle flow, is calculated by first computing the changes in the following control variables each control cycle:

■ antisurge PI control variable, dCVAS

■ limiting control variable, dCVLim

■ recycle-balancing control variable, dCVRB

■ valve-sharing control variable, dCVVS

Figure 3-8 gives the functional diagram for the Antisurge Controller. As shown in the diagram, the highest of these dCVs for the cycle is signal selected by the controller.

The Recycle Trip response, dCVRT, is then added to the signal-selected dCV:

dCV = dCVsignal selected + dCVRT

At this point, the dCV and the Recycle Trip opening response (dCVRT, opening) are passed to the companion controllers for loop decoupling. (The Recycle Trip decay response is not decoupled.) A CV value, used only for loop decoupling, is calculated by incrementing its value from the previous cycle by the dCV and dCVRT, opening for the current cycle:

CVn = CVn-1 + dCV + dCVRT, opening

Note: When the value of CV exceeds |3.0|, it will roll back to zero.

The Pressure Override Control variable dCVPOC is then signal selected with the dCV, as shown in Figure 3-8.

The dCV parameter gives the current value of the signal-selected control response of the Antisurge Controller. The Current dCV parameter indicates which control response is currently selected.

April 20, 1998


Figure 3-8 Antisurge Controller Functional Diagram

ManualOperation

Valve FlowCharacterizer

Valve Dead-Band Bias

OutputClamps

UpDown

TightShutoff

OutputReverse

Display

LimitingControl

RecycleTrip

RecycleBalancing

Ps Limit SPPd Limit SP

Σ LoopDecoupling

LoadSharing

Inputs

Calculate S& Deviation

Proximityto Surge

DerivativeResponse

Ss

CRD CRSO

Σb

Control LineCharacterizer

f4

Safety On &

Dev

Mass Flow

R

S

CV Total

Ps Pd

dPo

Pd

dCVRT

AntisurgePI

dCV

dCVLim

dCVLDdCVLS

dCVAS dCVRB

dCVVSValve

Sharing

OverridePressureCV

∫

or

Output

or

ManualTarget

ControlOverride

dCVPOCfor Loop Decoupling Control

(Intended Recycle Flow)

Intended

Output

Rc Limit SP

ΣdCVSignal Selected

dCV

EAS SurgeDetection

∫

ValvePosition



In order to counteract potentially destabilizing interactions with other controllers, the Antisurge Controller calculates a loop-decoupling response, dCVLD. In a series or parallel compressor application, the controller also calculates a load-sharing response, dCVLS . These responses are also added to the signal-selected dCV control response.

The dCV is finally added to the CV Total for the previous cycle to obtain a new value for CV Total, which represents the intended recycle flow:

CV Totaln = CV Totaln-1 + dCV + dCVLD + dCVLS

CV Total is the output of the Antisurge Controller before various control element compensation features are applied.

Each of the control functions and features shown in the functional diagram are presented in the following sections.

■ Proximity to Surge (page 3-1)

■ Control Line Characterizer (page 3-8)

■ Mass Flow (page 3-22)

■ Derivative Response (page 3-41)

■ Safety On (page 3-47)

■ EAS Surge Detection (page 3-50)

■ Calculate S & Deviation (page 3-69)

■ Recycle Trip (page 3-42)

■ Limiting Control (page 3-52)

■ Antisurge PI (page 3-40)

■ Recycle Balancing (page 3-67)

■ Valve Sharing (page 3-57)

■ Pressure Override Control (page 3-60)

■ Load Sharing (page 3-64)

■ Load Balancing (page 3-67)

■ Loop Decoupling (page 3-63)

■ Output Clamps (page 3-72)

■ Valve Flow Characterizer (page 3-73)

■ Valve Dead-band Bias (page 3-75)

■ Tight Shutoff (page 3-76)

■ Output Reverse (page 3-77)

■ Control Override (page 3-77)

■ Manual Operation (page 3-89)

April 20, 1998


General PIDAlgorithm

The following Proportional-Integral-Derivative (PID) algorithm is used to compute the control variable changes (dCV) during each control cycle for both the antisurge PI and limiting PID control variables:

where:

dCV = change in PI control variable

∆P = change in the proportional term of the algorithm

∆I = change in the integral term of the algorithm

∆D = change in the derivative term of the algorithm

Kp = proportional gain

e'n = dead-zone error for this iteration of the algorithm

e'n-1 = dead-zone error for the previous iteration of the algorithm

e'n-2 = dead-zone error for the second previous iteration of the algorithm

Ki = integral gain (reset rate in repeats per minute)

Kd = derivative gain (reset rate in minutes)

tc = scan time (in minutes)

Independent proportional, integral, and derivative gains (Kp, Ki, and Kd) are defined for each control loop which uses this algorithm.

The PI algorithm also includes several auxiliary features that can be enabled or disabled to meet process requirements. These functions are described in the following sections.

dCV P∆ I∆ D∆+ +=

P∆ Kp e'n e'n 1––( )⋅=

I∆Kp K⋅ i tc⋅

2-------------------------- e'n e'n 1–+( )⋅=

D∆ Kdtc

------- e'n 2e'n 1–– e'n 2–+( )⋅=



PID Span andDirection

The span for each PID loop defines the scale of its error variable relative to that of its set point and process variable, while the direction determines whether the control variable increases or decreases as its set point rises relative to its process variable.

For a direct-acting loop, the error (e) is calculated as:

where:

e = error

SP = set point

PV = process variable

span = span (see Table 3-9 below)

Thus, the error (and eventually the control variable) will increase in response to an increasing set point.

For a reverse-acting loop, the error is calculated as:

Thus, the error (and eventually the control variable) will decrease in response to an increasing set point.

The span of the antisurge PI control loop and direction of all control loops are predefined to the values shown in the following table and cannot be changed. The spans of the limiting control loops are configurable using the Pd Span, Ps Span, and Rc Span parameters.

Table 3-9 Span and Direction of PI Control Loops

e SP PV–span

----------------------=

e PV SP–span

----------------------=

PID Control Loop Span Direction

Antisurge PI loop 2.0 reverse

Pd limiting control loop Pd Span reverse

Ps limiting control loop Ps Span direct

Rc limiting control loop Rc Span reverse

April 20, 1998


PID Dead Zone In order to prevent minor process disturbances and signal noise from causing continual changes in its control variable, the PID algorithm will ignore insignificant differences between its process variable and set point.

The maximum deviation that each loop will ignore is defined by its dead-zone bias, which is added to or subtracted from the process error, e (as defined by the loop direction and span) to obtain the dead-zone error, e', as shown in the following table:

The dead zone is illustrated in Figure 3-9.

Figure 3-9 Dead-Zone Error (e') Plotted as a Function of Actual Process Error

Currently, the Antisurge Controller allows the user to define a dead zone for each PI loop using the following parameters:

■ Surge DZ (antisurge PI loop)

■ Pd PID DZ (discharge pressure limiting loop)

■ Ps PID DZ (suction pressure limiting loop)

■ Rc PID DZ (compression ratio limiting loop)

Setting a dead-zone parameter to zero disables the corresponding dead zone. These parameters must be specified in SI units.

When e' equals

e < –dead zone e + dead zone–dead zone ≤ e ≤ dead zone 0

e > dead zone e – dead zone

e'

e

Dead Zone

Dead Zone



PID VelocityClamps

The magnitude of the control variable change (dCV) calculated by each PID loop is limited by its velocity clamps, which are defined for all control loops by the PID Velocity High Limit and PID Velocity Low Limit parameters:

PID Velocity Low Limit < dCV < PID Velocity High Limit

In addition, the user can define absolute limits for the Display Output parameter (see Output Clamps on page 3-72).

Antisurge PIResponse

The Antisurge Controller uses a Proportional-plus-Integral (PI) response to increase the recycle rate when small, slow disturbances move the operating point to the left of the Surge Control Line (SCL), and to reduce it when operating to the right of the SCL.

The PI algorithm is used instead of PID because a standard derivative response would open the antisurge valve any time the compressor moved toward surge, even if there was no real danger of surging. This would result in frequent, unnecessarily wasteful recycling. Instead, the Antisurge Controller uses a special derivative response (see Derivative Response on page 3-41) to counter fast disturbances by raising the Safety Margin.

Changes in the antisurge PI response are calculated using the general PID algorithm (see page 3-38), with the value of S as the process variable and one as the set point:

where:

e = error

S = position of operating point relative to SCL (see Operating Point on page 3-12)

1 = set point

Thus, the change in the Antisurge PI control variable (dCVAS) will increase when the operating point is to the left of the SCL (the Deviation is negative).

e S 1–2.0

-------------=

April 20, 1998


The derivative term of the antisurge PI control response is forced to zero by predefining the derivative gain (Kd) as zero. The remaining factors in this PI loop are governed by the following parameters:

■ Surge DZ defines the dead-zone bias, in SI units.

■ Surge Kp defines the proportional gain.

■ Surge Ki defines the integral gain.

■ PID Velocity High Limit and PID Velocity Low Limit define the velocity clamps.

DerivativeResponse

The derivative response varies the Safety Margin (b) as a function of the rate at which the operating point of the compressor is approaching the Surge Limit Line (SLL). By automatically increasing b when the danger of surge is high, this feature allows the Safety Margin to be kept small (for maximum efficiency) when the danger of surge is small. (Refer to Safety Margin (b) on page 3-10 for more information.)

This feature is enabled by setting the Derivative Response Enable parameter to On. When the compressor is starting, stopping, or running, and the operating point is moving toward the SLL, the derivative response is calculated as:

where:

CRD = derivative control response

Tc = derivative response gain (Derivative Response Tc)


dSs/dt = derivative of Ss with respect to time

db = derivative response dead band (Derivative Response DB)

To reduce the effects of signal noise, the calculated value of dSs/dt is passed through a first-order-lag software filter. The S Tf parameter is used to set the time constant for this filter, in seconds. The dSs Max parameter shows the maximum value of dSs/dt that has occurred.

CRD Tc td

dSs db– =



A failure in the Ss process variable will cause dSs/dt to be zero and inhibit the derivative response of the Antisurge Controller.

The calculated value of CRD is then compared to the maximum derivative response, specified using the Derivative Response Max parameter. The smaller of the two values is used as the derivative control response.

When the operating point is to the right of the SLL and the value of CRD has decreased since the last cycle, the derivative response is ramped back to zero at the rate specified by the Derivative Response Rate parameter.

Recycle TripResponse

The Recycle Trip response protects the compressor from disturbances that are too large or fast to be countered by the PI and derivative response algorithms. When the operating point of the compressor moves to the left of the Recycle Trip Line (RTL), the Recycle Trip response quickly steps the recycle valve open to prevent the operating point from moving too close to the Surge Limit Line (SLL).

The distance between the operating point and the RTL, called the Recycle Trip deviation (devRT), is calculated as:

where:

devRT = Recycle Trip deviation (distance between the operating point and the RTL)


b1 = initial Safety Margin (SO Initial)

b2 = Safety On incremental bias based on number of surges

n = number of surges (Surge Count)

RT = Recycle Trip distance (RT Distance)

f4 = control line characterizer (f4 Characterizer)


devRT Ss 1– b1 b2 n⋅( ) RT–+[ ]+ f4 Z4( )⋅=

April 20, 1998


When a Recycle Trip response is triggered, the controller sets the RT parameter and any RT digital outputs and causes the Recycle Trip LED on the Operator Interface Module (OIM) to illuminate. These are cleared when normal PI control is restored. The RT Count parameter gives the number of Recycle Trip responses which have occurred.

The step size of the Recycle Trip response (dCVRT) is based on the setting of the RT Derivative Response Enable parameter (see next section), and is restricted to be between zero and the maximum Recycle Trip step size (RT Max Amplitude):

The Recycle Trip steps are added to the signal-selected response change (dCV), as shown in the functional diagram on page 3-35. The Recycle Trip step changes will continue to be added to the control response at intervals defined by the RT Deadtime parameter as long as the operating point is to the left of the RTL.

Note: If the compressor has surged, the Safety On function will shift the RTL to the right, thus triggering the Recycle Trip response sooner. Refer to Safety On Response on page 3-47 for more information.

The Emergency Antisurge (EAS) algorithm will cause a Recycle Trip response. See EAS Surge Detection on page 3-50 for more information. A Recycle Trip response caused by an EAS will use the maximum Recycle Trip step size.

0 dCVRT MaxRT≤ ≤



Recycle TripDerivativeResponse

The step size of the Recycle Trip response is based on the setting of the RT Derivative Response Enable parameter.

When RT Derivative Response Enable is set to On, the calculated size of each valve step includes a derivative term.

where:

dCVRT = Recycle Trip step size

MaxRT = maximum Recycle Trip step size (RT Max Amplitude)

KpRT = Recycle Trip proportional gain (RT Kp)

devRT = Recycle Trip deviation (see page 3-42)

KdRT = Recycle Trip derivative gain (RT Kd)


dSs/dt = derivative of Ss with respect to time

The derivative term (KdRT ⋅ dSs/dt) allows the recycle valve to be opened using smaller steps when the operating point is moving slowly past the RTL, instead of unnecessarily opening the valve at the maximum step amplitude.

If the approach to surge is rapid, the derivative term will usually restore a safe operating point before the proportional term (KpRT ⋅ devRT) becomes significant. However, if the approach to surge is slow, the derivative term might never become significant. In such cases, the proportional term would increase the step size until the accumulated Recycle Trip response increased the recycle rate enough to move the operating point back to the Surge Control Line (SCL).

These Recycle Trip step changes will continue to be added to the control response at intervals defined by the RT Deadtime parameter as long as the operating point is to the left of the RTL and dSs/dt is positive.

In applications where the flow measurement contains excessive noise, the derivative aspect of the Recycle Trip response should be disabled by setting the RT Derivative Response Enable parameter to Off. The Recycle Trip response will then generate steps of constant magnitude equal to the RT Max Amplitude parameter as long as the operating point is to the left of the RTL:

dCVRT Max= RT KpRT devRT⋅ K+ dRT td

dSs⋅

April 20, 1998


The derivative action of the Recycle Trip response can also be disabled by setting the RT Kd parameter to zero, in which case the step size would be:

where:

dCVRT = Recycle Trip step size

MaxRT = maximum Recycle Trip step size (RT Max Amplitude)

KpRT = Recycle Trip proportional gain (RT Kp)

devRT = Recycle Trip deviation (see page 3-42)

Recycle Trip dSsResponse

The Recycle Trip response can also be initiated based on the derivative of the proximity-to-surge variable (dSs/dt). If dSs/dt is greater than the value specified by the RT dSs Level parameter for an amount of time greater than that specified by the RT dSs Delay parameter, the recycle valve will step open by the amount configured with the RT dSs Response parameter.

If the normal Recycle Trip step response and the dSs/dt RT response are triggered simultaneously, the controller will select the larger response.

The Recycle Trip dSs response can be disabled by setting the RT dSs Level or RT dSs Delay parameters to high values and setting RT dSs Response to zero.

PI ResponseDuring

Recycle Trip

The antisurge PI response (dCVAS) is comprised of a proportional response (dCVP) and an integral response (dCVI):

dCVAS = dCVP + dCVI

When the operating point crosses to the left of the Recycle Trip Line (RTL), the proportional response is temporarily set to zero, therefore:

dCVAS = 0 + dCVI

dCVRT MaxRT=

dCVRT MaxRT KpRT devRT⋅ ⋅=



When the operating point crosses back to the right of the RTL, the reset rate is reduced using the following equation:

where:

dCVAS = antisurge PI response

dCVI = integral portion of antisurge PI response

KiADJ = reset rate adjustment (Ki Adjust)

Slowing the integral response in this way returns the operating point to the Surge Control Line (SCL) more slowly than it would otherwise. Normal operation of the antisurge PI response is restored when any one of the following conditions is met:

■ the antisurge PI error reaches zero;

■ the Display Output reaches its low clamp; or

■ the operating point has been to the right of the RTL for two minutes (if Surge Ki < 2.0) or five minutes (if Surge Ki > 2.0).

The RT parameter and any RT digital outputs are cleared when normal PI control is restored, and the Recycle Trip LED on the Operator Interface Module (OIM) will turn off.

Recycle TripManual Override

The detection of a Recycle Trip event will cause the controller to switch from manual operation to automatic operation when the manual override function is disabled (Manual Override is Off). This prevents a user from accidentally inducing surge by closing the recycle valve too far or by inadvertently leaving the controller in Manual.

If Manual Override is set to On, the user can manually override this feature and adjust the output to any value, even if it causes the compressor to surge. Setting a Stop or ESD request while Manual Override is enabled will cause the controller to go to Manual Shutdown, in which case the Recycle Trip function is inactive.

Warning! Enabling the Manual Override parameter is not recommended because it leaves the compressor unprotected from surge.

dCVPI 0dCVI

KiADJ--------------

+=

April 20, 1998


Recycle TripStatus

The status of the Recycle Trip function within the Antisurge Controller is given by the RT Status parameter. The possible values of this parameter are given in Table 3-10.

Table 3-10 Recycle Trip Status

When the operating point is to the left of the Recycle Trip Line (RTL), the status parameter will be set to ACTIVE. When the operating point returns to the right of the Surge Control Line (SCL), the status will switch to DECAYING while the integral portion of the antisurge PI response is being reduced using the Ki Adjust parameter, as discussed above. RT Status will switch to INACTIVE when the normal antisurge PI response is restored.

Recycle TripTest Response

A single, maximum Recycle Trip step response (dCVRT = MaxRT) can be initiated by setting the Recycle Trip Test parameter.

Refer to Operating Mode Selection on page 5-9 for information on performing this test using an Operator Interface Module (OIM).

Safety OnResponse

Changes in the process, wear and tear on the compressor, or severe disturbances can cause a compressor to surge despite the preventive efforts of the PI, derivative, and Recycle Trip responses. In such cases, the Safety On response reduces the likelihood of another surge event by moving the Surge Control Line (SCL) and Recycle Trip Line (RTL) to the right.

As discussed on page 3-11, the Safety On Line (SOL) defines an operating limit beyond which the compressor is assumed to be surging. The distance between the SOL and Surge Limit Line (SLL), referred to as the Safety On Distance, is determined by applying the f4 characterizing function to the specified value of the SO Distance parameter:


RT Status Description

INACTIVE Recycle Trip inactiveACTIVE Recycle Trip activeDECAYING Recycle Trip output ramping down after Recycle Trip active



A Safety On response is triggered when either of the following occurs:

1. The operating point crosses the Safety On Line:

Ss > 1+ SO Distance · f4(Z4)

2. The emergency antisurge (EAS) algorithm detects a surge (see EAS Surge Detection on page 3-50).

Each time a Safety On response is triggered, the Surge Count is incremented by one. When the Surge Count is greater than zero, the SO parameter is set to On.

The Safety On control response (CRSO) is equal to the initial Safety On margin (b1), which defines the minimum distance between the SLL and SCL, the accumulated Safety On bias (b2, n) corresponding to the current number of surges (n), and the additional Safety On margin (b4):

CRSO, n = b1 + b2,n + b4

where:

CRSO, n = Safety On control response

b1 = initial Safety On margin (SO Initial)

b2,n = accumulated Safety On bias(b2,n = b2,n-1 + SO Bias)

n = current number of surges (Surge Count)

b4 = additional Safety On margin (SO b4)

Therefore, when the surge count is zero, CRSO is equal only to the initial Safety On margin (SO Initial). With each additional surge event, the Safety On bias (SO Bias) is added again to the accumulated Safety On bias (b2), thus increasing the Safety On response (CRSO).

For example, Table 3-11 gives values of CRSO calculated for each surge count, assuming an initial Safety On margin of 0.25 and an SO Bias of 0.02. This example assumes that the SO Bias is changed by the user from 0.02 to 0.04 after the second surge. Note that the accumulated Safety On bias is zero when the surge count is zero.

April 20, 1998


Table 3-11 Example Safety On Accumulated Response

Since the Safety Margin (b) is the sum of the Safety On response and the Derivative response (see Safety Margin (b) on page 3-10), increasing the Safety On response will also increase the Safety Margin, thus moving the SCL and RTL to the right and reducing the likelihood of subsequent surges.

The additional margin of safety, b4, is added to the Safety On control response when the Load Sharing Controller is not running and the check valve is open. It is ramped to the value specified by the SO b4 parameter. The ramping rate when b4 is increasing is specified using the SO b4 Rate parameter. The ramping rate when b4 is decreasing is specified using the Derivative Response Rate parameter.

When the SO Time Based Enable parameter is set to On, surge detection is suspended after a surge event for the period of time specified by the SO Dead Time parameter. This allows time for the operating point of the compressor to move back to the right of the SOL before another Safety On response is triggered. If the operating point is still to the left of the SOL after the dead time has expired, the Surge Count will be incremented and another Safety On response will be triggered.

When the SO Time Based Enable parameter is Off, the operating point must move back to the right of the Surge Limit Line (SLL) after a surge event, before another Safety On response can be triggered. This is done to prevent a single surge event from triggering the Safety On response more than once.

Setting the Surge Count Reset parameter or the SO Reset digital input will reset CRSO, reduce the Surge Count to zero, reset the SO parameter to Off, reset the accumulated Safety On bias (b2) to zero, and initialize the PID to prevent a bump in the controller output. However, it is important to first

Surge Count (n)

SO Initial(b1)

SO Bias Accumulated Safety On

bias (b2)

CRSO

0 0.25 0.02 0 0.25

1 0.25 0.02 0.02 0.27

2 0.25 0.02 0.04 0.29

3 0.25 0.04 0.08 0.33

4 0.25 0.04 0.12 0.37

5 0.25 0.04 0.16 0.41



determine why the compressor has surged, and to make any appropriate adjustments to the Safety Margin.

Enabling the Surge Count Shutdown Reset parameter configures the controller to automatically zero the Surge Count and the accumulated Safety On bias (b2) when the compressor enters the Shutdown operating state.

The controller also accumulates a total surge count, given by the value of the Surges parameter, that is incremented each time a surge is detected. Unlike the Surge Count parameter, Surges must be manually set to zero.

When configured, the Exc Surge parameter and Surge digital output are set to On when the Surge Count meets or exceeds the value specified by the Surge Relay Threshold parameter. Exc Surge is reset to Off when Surge Count Reset is set to On; when the SO Reset digital input is asserted; or upon entering the Shutdown state when Surge Count Shutdown Reset is On.

Refer to Operating Mode Selection on page 5-9 for information on performing a Safety On reset using an Operator Interface Module (OIM).

EAS SurgeDetection

The Emergency Antisurge (EAS) algorithm detects compressor surge by comparing pressure and flow derivatives to specified rate-of-change thresholds:

■ If a flow-based EAS mode is selected, the rate of change of the suction flow is compared to the value of the dPo Rate parameter.

■ If a pressure-based EAS mode is selected, the rate of change of the discharge pressure (Pd) is compared to the value of the Pd Rate parameter.

When a pressure or flow derivative exceeds its threshold, the Surge Count parameter is incremented, a Recycle Trip response is triggered, and the EAS parameter is set to On. If the threshold is given a positive value, the Surge Count parameter is incremented when the selected derivative exceeds that limit. If the threshold is given a negative value, Surge Count is incremented when the derivative is more negative than the limit.

The EAS Mode parameter is used to specify the variable or variables that are compared to the rate-of-change thresholds. EAS Mode can be set to any of the values listed in Table 3-12.

April 20, 1998


Table 3-12 EAS Modes

For the DPO AND PD mode, if the Pd derivative reaches its threshold first, the dPo derivative must then reach its limit within the number of seconds specified by the Pressure->Flow Time Lag parameter. If the dPo derivative reaches its threshold first, the Pd derivative must then reach its limit within the number of seconds specified by the Flow->Pressure Time Lag parameter.

Setting either time lag to zero disables the corresponding test. For example, if Flow->Pressure Time Lag is zero, the Surge Count parameter is incremented only if the Pd rate-of-change reaches its limit first, after which the dPo derivative must reach its threshold before the Pressure->Flow Time Lag expires.

As an aid to setting the dPo Rate and Pd Rate thresholds, the controller records the most negative and most positive derivatives of the flow and discharge pressures, which can be accessed by the Max +dPo, Max -dPo, Max +dPd, and Max -dPd parameters. Appropriate limits can be determined by setting these parameters to zero before surge-testing the compressor.

EAS Mode Description

DISABLED EAS detection disabled.DPO AND PD EAS detected when both the flow derivative exceeds

dPo Rate and the discharge pressure derivative exceeds Pd Rate.

DPO OR PD EAS detected when either the flow derivative exceeds dPo Rate or the discharge pressure derivative exceeds Pd Rate.

DPO EAS detected when the flow derivative exceeds dPo Rate.

PD EAS detected when the discharge pressure derivative exceeds Pd Rate.



Limiting ControlResponse

The Antisurge Controller uses its general PID algorithm (see page 3-37) to calculate control responses to deviations of the suction pressure (Ps), discharge pressure (Pd), and compression ratio (Rc) from their limiting control threshold set points:

■ The suction pressure control variable (dCVPs) is calculated as a PID response to the deviation of the Ps Limit PV parameter from the Ps Limit SP.

■ The discharge pressure control variable (dCVPd) is calculated as a PID response to the deviation of the Pd parameter from the Pd Limit SP.

■ The compression ratio control variable (dCVRc) is calculated as a PID response to the deviation of the Rc parameter from the Rc Limit SP.

The status of the limiting control loops are given by the Ps Limit Status, Pd Limit Status, and Rc Limit Status parameters. The possible values of these parameters are described in Table 3-13.

Table 3-13 Limiting Control Loop Status

When the Ps Limit Enable, Pd Limit Enable, or Rc Limit Enable parameters are Off, the corresponding status parameter will be set to DISABLED.

When one or more limiting control loop is beyond its specified limit, the controller will set dCVLim equal to the highest of the limiting control responses. The controller will then set the status parameter for the selected response to ACTIVE, set the Limit parameter and any Limit digital outputs to On, and illuminate the limit LED on the Operator Interface Module (OIM). The status parameters for the nonselected limiting loops will remain set to INACTIVE.

When the limiting condition is restored to an acceptable level, the applicable limit status parameter will be set to DECAYING while the proportional response of the limiting control loop is

Ps Limit StatusPd Limit StatusRc Limit Status

Description

DISABLED limiting control loop OffINACTIVE limiting control loop out of limit conditionACTIVE limiting control loop in limit conditionDECAYING limiting control loop ramping down after limit

condition

April 20, 1998


set to zero, and the integral portion is reduced by dividing the integral response by the Ki Adjust parameter:

where:

dCVLim = limiting control PI response

0 = proportional term of limiting control PI response

dCVI, Lim = integral term of limiting control PI response


Slowing the integral portion of the limiting PI response in this way ramps down the value of dCVLim more slowly than it would otherwise, in order to keep the controller from immediately going back into a limit condition. When the controller Deviation reaches zero or the Display Output reaches its low clamp (or is below its low clamp when remote low clamping is used), the status parameter for the limiting control loop will switch to INACTIVE.

SuctionPressure

Limiting

The suction pressure limiting function is enabled by setting the Ps Limit Enable parameter to On. Changes in the suction pressure control response (dCVPs) are then calculated by the general PID algorithm (see page 3-37):

where:

e = error

SP = suction pressure limiting set point (Ps Limit SP)

PV = suction pressure process variable (Ps Limit PV)

span = suction pressure span (Ps Span)

Thus, dCVPs will increase when the suction pressure is below its limiting control threshold. (Refer to PID Span and Direction on page 3-38 for more information.)

dCVLim 0dCVI, Lim

KiADJ-----------------------

+=

e SP PV–span

----------------------=



The remaining aspects of this loop are governed by the following parameters:

■ Ps PID DZ defines the dead-zone bias, in SI units.

■ Ps PID Kd defines the derivative gain.

■ Ps PID Kp defines the proportional gain.

■ Ps PID Ki defines the integral gain (reset rate).

■ Ps PID Tf defines the time filter.


The set point for this loop can be controlled by an analog input or defined as a constant. In either case, it is always set equal to Ps Limit SP Default when the controller is first powered up. To define the set point as a constant, the Ps Limit SP Default is set equal to the desired value. If the controller is already running, the set point can be temporarily changed by entering a new value for Ps Limit SP. To permanently change it, both Ps Limit SP and Ps Limit SP Default must be set equal to the desired new value.

The status of the suction pressure limiting control loop is given by the Ps Limit Status parameter, as described in Table 3-13.

DischargePressure

Limiting

The discharge pressure limiting function is enabled by setting the Pd Limit Enable parameter to On. Changes in the discharge pressure control response (dCVPd) are then calculated by the general PID algorithm (see page 3-37):

where:

e = error

PV = discharge pressure process variable (Pd)

SP = discharge pressure limiting set point (Pd Limit SP)

span = discharge pressure span (Pd Span)

Thus, dCVPd will increase when the discharge pressure is above its limiting control threshold. (Refer to PID Span and Direction on page 3-38 for more information.)

e PV SP–span

----------------------=

April 20, 1998



■ Pd PID DZ defines the dead-zone bias, in SI units.

■ Pd PID Kd defines the derivative gain.

■ Pd PID Kp defines the proportional gain.

■ Pd PID Ki defines the integral gain (reset rate).

■ Pd PID Tf defines the time filter.


The set point for this loop can be controlled by an analog input or defined as a constant. In either case, it is always set equal to Pd Limit SP Default when the controller is first powered up. To define the set point as a constant, the Pd Limit SP Default parameter is set to the desired value. If the controller is already running, the set point can be temporarily changed by entering a new value for Pd Limit SP. To permanently change it, both Pd Limit SP and Pd Limit SP Default must be set equal to the desired new value.

The status of the discharge pressure limiting control loop is given by the Pd Limit Status parameter, as described in Table 3-13.

CompressionRatio

Limiting

The compression ratio limiting function is enabled by setting the Rc Limit Enable parameter to On. Changes in the compression ratio control response (dCVRc) are then calculated by the general PID algorithm (see page 3-37):

where:

e = error

PV = compression ratio process variable (Rc)

SP = compression ratio limiting set point (Rc Limit SP)

span = compression ratio span (Rc Span)

Thus, dCVRc will increase when the compression ratio is above its limiting control threshold. (Refer to PID Span and Direction on page 3-38 for more information.)

e PV SP–span

----------------------=




■ Rc PID DZ defines the dead-zone bias, in SI units.

■ Rc PID Kd defines the derivative gain.

■ Rc PID Kp defines the proportional gain.

■ Rc PID Ki defines the integral gain (reset rate).

■ Rc PID Tf defines the time filter.


The set point for this loop can be controlled by an analog input or defined as a constant. In either case, it is always set equal to Rc Limit SP Default when the controller is first powered up. To define the set point as a constant, the Rc Limit SP Default parameter is set to the desired value. If the controller is already running, the set point can be temporarily changed by entering a new value for Rc Limit SP. To permanently change it, both Rc Limit SP and Rc Limit SP Default must be set equal to the desired new value.

The status of the compression ratio pressure limiting control loop is given by the Rc Limit Status parameter, as described in Table 3-13.

IntegratedControl Features

In addition to providing surge protection and pressure-limiting control for any one section of a compressor, the Antisurge Controller can also cooperate with other Series 4 controllers to provide integrated control in virtually any application. This coordination is provided by the following features:

■ Valve Sharing is used for multisection compressors with only a single recycle valve (see page 3-57).

■ Pressure Override Control helps manage excessive deviations of the performance control process variable (see page 3-60).

■ Loop Decoupling counteracts potentially destabilizing interactions with the other Series 4 controllers (see page 3-63).

■ Load Sharing features are used for groups of compressors operating in series or in parallel (see page 3-64).

April 20, 1998


Valve Sharing In multicompressor applications, each compressor section should be equipped with its own Antisurge Controller, even if there is only a single recycle path and control valve for the entire machine, as shown in Figure 3-10. In such applications, the Valve Sharing function allows several Antisurge Controllers to share one recycle valve by keeping the recycle rate high enough to protect the section closest to its surge limit.

Figure 3-10 Protecting a Multisection Compressor with a Shared Recycle Valve

The controller that directly manipulates the antisurge valve is called the primary Valve Sharing Antisurge Controller. The secondary Valve Sharing Antisurge Controllers pass their control responses to the primary, which selects the highest PI and Recycle Trip responses.

For the primary controller, the Valve Sharing Mode parameter must be set to Primary. For secondary controllers, the Valve Sharing Mode parameter must be set to Secondary.

For series valve-sharing applications (as shown), the Series parameter is set to Series within each Valve Sharing Controller. For parallel applications it is set to Parallel.

The module addresses of the secondary controllers are entered into the Valve Sharing Companions parameter of the primary Antisurge Controller, with any unneeded elements of that array set to zero. Likewise, the Valve Sharing

Selected P

High-PressureSection

Low-PressureSection

Key:UIC1: Primary Valve-Sharing Antisurge ControllerUIC2: Secondary Valve-Sharing Antisurge Controller

UIC1

UIC2

FY

FT PTPT

FT PTPT

Selected I



Companions parameter within each secondary controller are set to the module address of the primary controller.

If the primary and secondary controllers are in different chassis, the following LTOP arrays must be configured within the Valve Sharing Controllers to obtain the required valve-sharing information:

■ VS S LTOP (to obtain S)

■ VS P LTOP (to obtain Selected P)

■ VS I LTOP (to obtain Selected I)■ VS CV LTOP (to obtain CV)

■ Antisurge Status LTOP (to obtain Status)

The following LTOP arrays must be configured within the Valve Sharing Controllers to obtain the required valve-sharing information:


■ Antisurge Status LTOP (to obtain Status)

The primary Valve Sharing controller monitors the response of each secondary Valve Sharing controller and selects the proportional and integral terms (Selected P and Selected I) of the secondary controller with the greatest change in the proportional term. When a response from a secondary Valve Sharing controller to open the recycle valve is signal-selected within the primary Antisurge Controller, the VS parameter within the primary controller will be set to On.

The primary controller then uses those proportional and integral terms in the calculation of its valve-sharing response:

dCVVS = dCVP + dCVI + dCVRT

where:

dCVVS = Valve Sharing response

dCVP = proportional term of Valve Sharing PI response (Selected Pn – Selected Pn-1)

dCVI = integral term of Valve Sharing PI response (Selected I)

dCVRT = Recycle Trip response of secondary controller (CVn – CVn-1)

April 20, 1998


When a Recycle Trip is triggered within a secondary Valve Sharing controller, the RT parameter within that controller is set to On and is passed to the primary controller. The RT and VS RT parameters within the primary controller are also set to On. The CV from the secondary controller is then passed to the primary controller and the valve opened by the amount of the CV change (dCVRT = CVn – CVn-1).

The status of the Valve Sharing function within the Antisurge Controller is given by the VS Status parameter. The possible values of this parameter are described in Table 3-14.

Table 3-14 Valve Sharing Status

When VS is On, the status parameter will be set to ACTIVE. When VS switches from On to Off, the status parameter will switch to DECAYING, and the integral portion of the Valve Sharing PI response will be reduced using the Ki Adjust parameter:

where:

dCVRT = Valve Sharing PI response

dCVI = integral term of Valve Sharing PI response

dRTVS = Recycle Trip response of secondary controller


Slowing the integral portion of the Valve Sharing PI response in this way ramps down the value of dCVVS at a rate slower than the normal PI response. This is done to prevent whatever caused the secondary controller to open the recycle valve from causing the valve to immediately open again. When the Deviation for the Valve Sharing PID loop reaches zero, or the Display Output reaches its low clamp (or is below its low clamp when remote low clamping is used), VS Status will switch to INACTIVE.

VS Status Description

DISABLED Valve Sharing disabledINACTIVE Valve Sharing inactiveACTIVE Valve Sharing activeDECAYING Valve Sharing output ramping down after Valve

Sharing active

dCVVS

dCVI

KiADJ--------------

dCVRT+=



PressureOverride Control

When the primary variable of the performance control system rises too high or too fast (flow or discharge pressure) or falls too low (suction pressure), it can quickly be restored to an acceptable level by raising the recycle rate in addition to throttling back the compressor. With a Series 4 Controller, this is accomplished using the Pressure Override Control (POC) function.

The POC function allows the Antisurge Controller (using the antisurge valve) to assist in regulating the primary performance variable whenever it moves above or below its POC set point by a preset level. The POC function can only move the antisurge valve in the open direction. Within a companion Antisurge Controller the POC function is enabled by setting the POC Enable parameter to On.

The POC function uses companion Antisurge Controllers linked to a single Master Performance Controller. Within each Antisurge Controller, the Master parameter is used to designate the Performance Controller to which the controller is linked.

When the Master and Antisurge Controllers are in different chassis, the POC CV LTOP parameter is used within the Antisurge Controller to designate the location of POC CV in the Master Controller. Similarly, the Master Status LTOP parameter is used to designate the location of the Status parameter in the Master Controller.

The Master Performance Controller calculates a control variable (POC CV) based on the deviation of its POC process variable from its POC set point. (Refer to UM4104, Using the Series 4 Performance Controller AFM, for more information.) When a POC process variable exceeds its set point, the corresponding POC Valid parameter within the Master Controller is set to On.

When the POC Valid parameter within the Master Controller is On, the POC parameter within the Antisurge Controller will also be set to On. The change in the POC control variable from the Master will then be compared with the value of the dCV within the Antisurge Controller (as shown in the functional diagram on page 3-35), and the highest value selected.

When the POC delta control variable is selected as the output of the Antisurge Controller, the Limit LED on the Operator Interface Module (OIM) will blink. The POC dCV parameter gives the value of the POC delta control variable, which is the

April 20, 1998


sum of the POC control variable from the Master and the filtered POC response (dCVPd) discussed in the next section.

The status of the POC function within the Antisurge Controller is given by the POC Status parameter. The possible values of these parameters are described in Table 3-15.

Table 3-15 POC Status

When POC Enable is Off, the status parameter will be set to DISABLED. When POC is On, the status parameter will be set to ACTIVE. When POC switches from On to Off, the status parameter will switch to DECAYING, and the integral portion of the Antisurge PI response will be reduced using the Ki Adjust parameter:

where:

dCVPOC = POC PI response

dCVI = integral term of Antisurge PI response


Slowing the integral portion of the POC PI response in this way ramps down the value of dCVPOC more slowly than it would otherwise, in order to prevent the POC response from immediately being triggered again. When the Deviation reaches zero, or the Display Output reaches its low clamp (or is below its low clamp when remote low clamping is used), POC Status will switch to INACTIVE.

POC Status Description

DISABLED POC disabledINACTIVE POC inactiveACTIVE POC activeDECAYING POC output ramping down after POC active

dCVPOC 0dCVI

KiADJ--------------

+=



Filtered POCResponse

The Antisurge Controller calculates a filtered POC response to look for rapid increases in discharge pressure. The POC PV Tf parameter is used to specify the time constant for this filter. The filtered response is calculated using the following equation:

where:

dCVPd = filtered POC response for Pd

KPOC = POC filtered gain (POC Filtered Gain)

Pd = discharge pressure (Pd)

Pd, filter = filtered value of Pd

ThresholdPOC = POC filtered threshold (POC Filtered Threshold)

span = discharge pressure span (Pd Span)

The POC Filtered Gain parameter is used to adjust the strength of the Pd filtered response.

When the difference between the discharge pressure (Pd) and its filtered value (Pd, filter) exceeds a specified threshold (POC Filtered Threshold), a filtered response (dCVPd) will result. The POC Filtered Delta parameter gives the current difference between the Pd and the filtered Pd. The POC Filtered Delta Max parameter gives the maximum value of the POC Filtered Delta, and can be reset to zero.

The Filtered POC Valid parameter indicates that the filtered POC response is greater than zero.

The filtered POC response for the discharge pressure has a low clamp at zero. When dCVPd is greater than zero, it is added to the POC control variable (POC CV), and is signal-selected within the Antisurge Controller when POC is enabled.

dCVPd KPOC

Pd Pd, filter–( ) ThresholdPOC–

span------------------------------------------------------------------------------⋅=

April 20, 1998


Loop Decoupling The potentially destabilizing effects that could result from interactions between the performance and antisurge control loops (or the various antisurge loops of a multisection compressor) can be counteracted by the Loop Decoupling function.

During each scan cycle, the Antisurge Controller calculates the change in its Loop Decoupling control variable (dCVLD) by applying gains to the change in the loop-decoupling control variable (CV) obtained from the data packet of each designated companion controller:

where:

dCVLD = loop-decoupling response

i = summation index

Mi = decoupling gain defined by the ith elementof LD Companions Coefficient

(CVn – CVn–1)i = the change between the loop-decouplingcontrol variables obtained in the currentcycle (CVn) and the previous cycle (CVn–1),designated by the ith element of LD Companions

The loop decoupling response (dCVLD) is added to the intended recycle flow output (CV Total) of the Antisurge Controller, as described in Antisurge Controller Functions on page 3-34.

The LD Companions parameter is used to obtain the CVn values when the companion loop decoupling controllers are in the same chassis. When the companion loop-decoupling controllers are in different chassis, the Decouple CV LTOP parameter is used to designate the controllers from which to obtain the CVi values for loop decoupling. The LD Status LTOP parameter is used to obtain the values of the Status parameters from the companion controllers.

The Antisurge Controller obtains the CVs only from the companion Performance and Antisurge Controllers for which the LD Valid parameter is On. For a Performance Controller, LD Valid will be On when the controller is in the Run state and is not at a high or low clamp. For an Antisurge Controller, LD

dCVLD Mii 1=

10

∑ CVn CVn 1––( )i⋅=



Valid will be On when the controller is running, is not at a high or low clamp, and POC is inactive. LD Valid will also be On when the Antisurge Controller is in a run freeze fallback, if the controller is running.

The decoupling gains for companion Antisurge Controllers are applied only if their compressors are operating to the left of their Surge Control Lines (SCLs). If a companion Antisurge Controller is in Recycle Trip, the RT response will be included in the loop decoupling response of the receiving Antisurge Controller, regardless of whether this controller is operating to the left or right of the SCL.

The loop decoupling function is not active while the Antisurge Controller is in the Starting state.

Load Sharing For applications with a network of compressors operating in parallel or series, Series 4 Controllers use a number of load-sharing techniques to regulate the capacity and maximize the efficiency of the compressors. The following controllers are used in load-sharing applications:

■ One Master Performance Controller is used for each load-sharing network. This Master Controller regulates the overall performance of the compressor network, as shown in Figure 3-11 on page 3-65.

■ One Load Sharing Performance Controller is used for each compressor. The Load Sharing Controller regulates the performance of each compressor in the network.

■ One Antisurge Controller is used for each compressor stage. The Antisurge Controllers provide protection against surge for each compressor stage in the network.

■ A parallel compressor control system might also include a Cold Recycle (S) Controller (see page 3-69).

Load-sharing systems use complementary functions to regulate and distribute the overall throughput of a compressor:

■ The Load-Sharing Response allows a Master Performance Controller to regulate the flow or pressure in a header by indirectly manipulating the antisurge and performance control elements (for example, the recycle and throttle valves).

■ Load Balancing minimizes unnecessary recycling by keeping all compressor operating points the same distance from surge. Load balancing also equalizes the

April 20, 1998


recycle rates of compressors connected in series (see page 3-67).

■ Recycle Balancing equalizes the recycle rates of compressors operating in parallel (see page 3-67).

■ Pressure Override Control (POC) allows a Master Performance Controller to quickly restore a flow or pressure that has deviated from set point by manipulating the recycle valves (see page 3-60).

Figure 3-11 Load-Sharing Controller Configuration

Note: The following sections describe the implementation of these features in the Series 4 Antisurge Controller. Complete descriptions of these features can be found in UM4104, Using the Series 4 Performance Controller AFM.

Load-SharingResponse

The load-sharing response allows a Master Performance Controller to regulate the flow or pressure in a header by indirectly manipulating the compressor performance and antisurge control elements. In an Antisurge Controller, the load-sharing response will increase the recycle rate only when the compressor is close to its surge limit, and can never reduce the recycle flow rate.

The Antisurge Controller is configured for load sharing by setting the Master parameter to the address of the Master Performance Controller. The control variable of the Master Controller (CVMC) can also be obtained using the Master CV LTOP parameter. If communication is lost between the Load Sharing Controller and the Master Controller, the load-sharing response is set to zero.

...

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MasterPerformance

Load SharingPerformance

Controller1


Controller2


Controllern

AntisurgeController

1

AntisurgeController

2

AntisurgeController

n

Controller



The load-sharing response is calculated by applying a gain to the change in the control variable from the Master Controller:

where:

dCVLS = change in the Antisurge load-sharingcontrol variable

KLS = load-sharing gain (Load Share Gain)

CVMC, n – CVMC, n-1 = change in the control variables fromthe Master Controller obtained in thecurrent cycle (n) and the previouscycle (n-1)

The load-sharing gain (Load Share Gain) is set to 0 to turn off load sharing. The gain is applied only when the resulting dCVLS is positive (to increase the recycle rate) and the S variable indicates a sufficient danger of surge:

where:

S = proximity-to-surge variable, S (see page 3-10)

β3 = load-sharing threshold (Beta 3)

Otherwise, the load-sharing response of the Antisurge Controller is held constant (dCVLS = 0) and load sharing is achieved solely by manipulating the throttling element of the compressor using the load-sharing response of the Performance Controller.

The load-sharing response (dCVLS) is then added to the intended recycle flow output (CV Total) of the Antisurge Controller:


where:

CV Totaln = current Antisurge Controller output

CV Totaln-1 = Antisurge Controller output for previous cycle

dCV = PID control response

dCVLD = loop decoupling response

dCVLS = load-sharing response

dCVLS KLS CVMC, n CVMC, n-1–( )⋅=

S β3≥

April 20, 1998


Load-BalancingResponse

Master and Load Sharing Performance Controllers cooperate to keep all compressor operating points in a network the same distance from surge by equalizing a load-balancing variable calculated from the following Antisurge Controller parameters:

■ In a parallel load-sharing application, this load-balancing variable is based on the S variable.

■ In a series load-sharing application, this load-balancing variable is based on the S variable and total mass flow rate squared (R = W

2, see page 3-22). Equalizing this variable

also equalizes the compressor recycle rates.

These parameters are passed from an Antisurge Controller to its companion Load-Sharing Performance Controller for use in the load-balancing PID loop. The S value sent to a load-sharing controller does not include the CRD response.

Refer to UM4104, Using the Series 4 Performance Controller AFM, for detailed information on the load-balancing response.

RecycleBalancingResponse

The load-balancing algorithm used in parallel compressor applications (see Figure 3-12) is designed to avoid unnecessary recycling by equalizing each compressor’s proximity to surge. However, if the load declines to the point that recycling is unavoidable, the resulting recycle flow rates will not necessarily be equal. The recycle flow rates typically differ significantly, even if the compressors are identical and their controllers are tuned alike.

In some applications, it may be desirable to force equal recycle rates for all of the parallel compressors. For example, it might be important to maintain similar fluid temperatures in each branch of the compressor network. Balancing the recycle flows would help to satisfy that need.

The RB Companions parameter is used to designate the companion recycle-balancing Antisurge Controllers in a parallel compressor application. Each element of this parameter should be set equal to the module address of a companion controller. Unneeded elements must be set to zero. Setting all of the elements to zero disables this feature.



Figure 3-12 Simplified Parallel Compressor Configuration

An RB Valid parameter is passed from each controller to indicate that the CV Total from the controller is valid and can be used in the signal selection. Recycle balancing will be disabled and the RB Valid set to False when the Disable RB digital input is set.

The RB CV LTOP and RB Valid LTOP parameters can also be used to obtain the CV Totals from the recycle-balancing companion controllers.

Recycle balancing is accomplished by comparing the CV Total from each companion recycle-balancing Antisurge Controller, and signal-selecting the highest (Max CV Total).

Each companion recycle-balancing Antisurge Controller compares the Max CV Total to its own CV Total. When all of

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April 20, 1998


the following conditions are met in both this controller and the controller which produced the Max CV Total, the recycle-balancing control response (dCVRB) is included in this Antisurge Controller’s dCV signal selection, as discussed in Antisurge Controller Functions on page 3-34:

■ both controllers are in the Run state;

■ the difference between the Max CV Total and the CV Total is greater than 0.5 percent:

Max CV Total – CV Total > 0.5%;

■ the Deviation is less than 0.1; and

■ the compressor is not operating to the left of its Recycle Trip Line, or the controller output is not decaying after a Recycle Trip (see page 3-45).

The recycle-balancing control response (dCVRB) has a constant value defined by the RB Rate parameter.

Cold Recycle (S)Control

The load-sharing strategy for parallel compressors is easily adapted to networks that have an overall “cold” recycle loop in addition to a “hot” recycle loop on each compressor, as shown in Figure 3-13.

The hot recycle loops protect each individual compressor from surge due to sudden flow disturbances. However, if sustained recycling is necessary, the recycle flow is routed through the cold recycle loop, which includes a heat exchanger that cools the recycle gas. Heat buildup can be avoided without compromising surge protection and without the expense of multiple heat exchangers.

Series 4 Control Systems are adapted to such applications by adding a Cold Recycle (S) Controller to modulate the cold recycle valve. An Antisurge Controller can be configured for this application by setting its Numerator Mode, Denominator Mode, or dPos Mode parameter to S CONTROL (see page 3-5) and setting the elements of its S Controller Companions parameter equal to the module addresses of its companion hot-recycle Antisurge Controllers. Any unneeded elements of that array must be set to zero.



The following LTOP arrays must be configured to obtain the required information from the companion controllers:


■ VS P LTOP (to obtain Selected P)

■ VS I LTOP (to obtain Selected I)■ Antisurge Status LTOP (to obtain Status)

The Controller Type parameter indicates that a controller is configured as a Cold Recycle Controller (S CONTROL).

Figure 3-13 Cold Recycle Loop in a Parallel Network

The Cold Recycle (S) Controller selects the highest S value reported by any of its companions as the value of its proximity-to-surge variable, Ss. It then calculates its own S value by adding its Safety Margin (b).

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Compressor 1

Compressor 2

1

2

S2

April 20, 1998


In most cases, this added Safety Margin is defined as a constant by:

1. setting f4 Characterizer Mode to DISABLED;

2. setting SO Bias to zero; and

3. setting SO Initial equal to the desired Safety Margin.

This added margin assures that the Cold Recycle (S) Controller will reach its Surge Control Line and begin recycling before any of the Hot Recycle Controllers.

The I Offset parameter is added to the highest integral term from the companions to calculate the cold-recycle dCV. The P Offset parameter is used as an offset to the output instead of being added to cold recycle dCV. These offsets are also used to make sure that the cold-recycle valve opens first.

Except in the case of a rapid or large disturbance, opening the cold-recycle valve will provide enough extra flow to prevent surge, thus negating the need to open the hot-recycle valves.

A Cold Recycle (S) Controller will fall back to run freeze operation if it fails to receive any valid S values from its designated companions. Refer to Fallback Strategies on page 3-27 for more information.

While the S controller is shut down, the following conditions will affect the controller output as described:

■ When the ESD signal from the Series 4 Speed Controller changes from On to Off, the S controller Output will jump to the level specified by the S Control Start Level parameter.

■ If the speed (N) from a Series 4 Speed Controller exceeds the level defined by the S Control Start Speed parameter, the controller Output will start ramping toward the Output High Limit at the specified Start Rate.

■ When the ESD signal changes to On, the S controller Output will go to the Output Low Limit when the speed drops below the level specified by the S Control Stop Speed parameter.

To get the ESD information for the S controller, the user must do the following:

■ configure the ESD digital input, and

■ get the speed information through configuration of the LTOP through the analog input, or through Modbus.



Control ElementCompensation

The Output of the Antisurge Controller is the output signal used to control the recycle valve. As shown in the functional diagram on page 3-35, it is calculated by applying the following output transformations to the intended recycle flow (CV Total):

■ The output clamps (see below) limit the range of the output signal.

■ The valve flow characterization function (see page 3-73) adapts the output signal to the valve flow characteristics (for example, a quick-opening valve).

■ The valve dead-band compensation function compensates for valves with worn actuator linkages (see page 3-75).

■ The tight shut-off function allows the controller to fully close the valve when the minimum clamp is greater than zero (see page 3-76).

■ The output reverse function adapts the controller to a signal-to-open or signal-to-close valve (see page 3-77).

The controller also calculates a Display Output that represents the signal to a signal-to-open valve. The valve opens as this signal rises. The Output Reverse function is not applied to the Display Output.

Output Clamps The Output of the Antisurge Controller can be clamped within an allowable range using the Output Low Limit and Output High Limit parameters.

Note: These clamps are applied before the valve flow characterization, valve dead-band bias, tight shutoff and output reverse functions. The clamps are not applied when the controller is in the Manual state.

The High Clamp status parameter indicates that the Output is at its high limit. The Low Clamp status parameter is set when the Output is at the higher of the Output Low Limit or the minimum set by the remote clamp.

April 20, 1998


Remote LowClamping

The Antisurge Controller can also use an input as a remote low clamp for its Output:

■ If Output Reverse is disabled, the input must increase to increase the recycle flow rate.

■ If Output Reverse is enabled, the input must decrease to increase the recycle flow rate.

In either case, this signal actually defines a temporary minimum clamp for the Output. In effect, this allows the Antisurge Controller to share the recycle valve with another device, without risking integral windup or restricting the ability to open the valve as needed to prevent surge.

To use this feature, the input should be connected to any unused analog input, and the Remote Low Clamp element of the Analog Inputs LTOP configured appropriately. The remote clamp is disabled if no input is assigned.

The Remote Low Clamping parameter will be set to On when the valve output is limited by the input. The Track LED on the Operator Interface Module (OIM) will blink when remote low clamping is active (this LED will be On continuously when the control override function is active).

In the Manual state, an increasing remote low clamp input can raise the Manual Target and open the valve, but a decreasing input cannot close the valve. In the Run state, the PI response will close the valve when the remote low clamp input is decreasing.

Valve FlowCharacterization

If the Antisurge Controller is used with a recycle valve that exhibits inherently nonlinear flow characteristics, the valve flow rate can be linearized with respect to the controller output by using one of the valve characterization modes.

The Valve Mode parameter is used to specify the valve characterization mode applied to the controller output. The control response of the valve can be selected from linear, fast, slow, and characterization modes, as summarized in Table 3-16.



Table 3-16 Valve Characterization Modes

The Linear valve mode should be selected for valves with linear flow characteristics. This option assumes the flow is proportional to the valve opening.

The Fast valve mode should be selected for quick-opening valves. For these valves, the flow rate is assumed to be proportional to the square root of the fractional valve opening (for example, if the valve is 1/4 open, the flow would be 1/2 its maximum rate). Therefore, the actual output is obtained by squaring the flow rate calculated by the control algorithm.

The Slow valve mode should be selected for equal- percentage valves. For these valves, the flow rate is assumed to be proportional to the square of the fractional valve opening (for example, if the valve is 1/2 open, the flow would be 1/4 its maximum rate). The actual output is obtained by taking the square root of the intended flow rate calculated by the control algorithm.

Figure 3-14 illustrates the relationship between the calculated control response and the actual output signals for the linear, fast, and slow valve modes. In each case, the resulting flow rate will be approximately proportional to the output calculated by the controller.

Valve Mode Effect on Antisurge Controller Output

Linear Output = output (default)Fast Output = output squaredSlow Output = square root of outputCharacterization Output defined with the

Valve Characterizer parameter

April 20, 1998


Figure 3-14 Valve Flow Characteristic Response

The final valve mode, the Characterization mode, allows the user to enter the valve characterization data applied to the controller output. The valve characterization data is entered using the Valve Characterizer parameter.

When the Antisurge Controller is in the Manual state, the valve mode function is not applicable, and the valve characterization data cannot be applied to the valve output.

ValveDead-Band

Compensation

Due to wear or design imperfections, the mechanical response of a recycle valve may exhibit a dead band which must be overcome when the control action reverses direction. The valve dead-band bias function allows the Antisurge Controller to overcome this dead band effect by including a valve dead-band bias in its output signal.

This bias is added to the intended valve position when that signal is rising, and subtracted when it is falling. Thus, a change in the direction of the output is accompanied by a step change in the output with a magnitude equal to twice the bias value, as illustrated in Figure 3-15. The Valve Dead Band Bias parameter is used to specify the control valve dead band bias.

0 1

1

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Figure 3-15 Valve Dead-Band Compensation

When the intended valve position changes direction, it must move in the new direction a minimum amount before the bias is added in the opposite direction. This bias threshold value is specified using the Valve Dead Band Bias Threshold parameter.

The valve dead-band compensation function is applied to the output only in the Run state, and is not applied to the manual output when the Antisurge Controller is in the Manual state.

Tight Shutoff Ideally, when the intended valve position is at the low clamp, the recycle valve will be fully seated and the recycle flow path completely blocked. However, because of worn valves or valves with teflon seats, there may still be a slight leakage that wastes energy and produces an audible sound.

The solution is to force the Display Output to zero when the intended valve position is at the low clamp and the possibility of surge is low. This result is obtained by setting Tight Shut Off Distance to a nonzero value, thus defining a Tight Shutoff Line (TSL). The Tight Shut Off Distance defines the distance between the Surge Control Line (SCL) and the TSL (see Tight Shutoff Line on page 3-11).

The controller will force the Display Output to zero when the operating point of the compressor moves to the right of the TSL (Deviation > Tight Shut Off Distance · f4) and the intended valve position is at its low clamp.

Once the tight shut-off function is activated, the Display Output will remain at zero until operating conditions dictate that the recycle valve should be open. At this point, the Display Output will jump back to the Output Low Limit before the controller calculates a new control response.

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April 20, 1998


Output Reverse The Antisurge Controller is configured for either a signal-to-open (fails closed) or signal-to-close (fails open) control valve by setting its Output Reverse parameter:

■ For a signal-to-open valve, Output Reverse must be set to Off. The Output then equals the Display Output and increases when additional recycle flow is required.

■ For a signal-to-close valve, Output Reverse must be set to On. The Output then equals the compliment of the Display Output (1 – Display Output) and decreases when additional recycle flow is required.

Any analog output assigned to the Output parameter will vary from its minimum to its maximum value (for example, from 4 to 20 mA) as the Output ranges from zero to one. (Output Reverse would result in 20 to 4 mA.)

The Display Output represents the signal to a signal-to-open valve. The valve opens as this signal rises. The Output Reverse function is not applied to the Display Output.

Control Override The control override function is used to track the value of an analog input to the Antisurge Controller. To utilize this feature, the desired analog input is connected to any unused analog input to the Antisurge Controller. The Analog Inputs LTOP array is then used to link the Control Override SP parameter to the value of the analog input.

The control override function is activated when the Control Override digital input is set to On. The Control Override parameter and digital output give the status of the control override function within the Antisurge Controller.

The Output of the Antisurge Controller will track the value of Control Override SP when the compressor is operating to the right of the Recycle Trip Line (RTL). If the Output is below the value of the Control Override SP, it is increased at the rate specified by the Output Tracking Rate parameter. If the Output is above the Control Override SP, it is decreased at that rate.

The Controller Status parameter will be set to TRACKING when the control override function is active. In addition, the Track LED on the Operator Interface Module (OIM) will be On continuously (this LED will blink when in remote low clamping).



The output clamps do not apply when the control override function is active. Therefore, the Control Override SP can adjust the Output to any value between zero and one.

When a Recycle Trip occurs with the control override function enabled and manual override Off, the Antisurge Controller will go to the Run state.

The control override function does not operate when the Antisurge Controller is in the Manual state.

Recycle ValvePosition

Feedback

The Antisurge Controller monitors the position of the recycle valve and generates an alarm if the position feedback signal fails, or if the difference between the position of the antisurge valve and the output of the controller exceeds a specified maximum. The Pos parameter indicates the current position of the recycle valve.

The Pos Delta Max parameter is used to specify the maximum allowable difference between the position of the antisurge valve (Pos) and the output of the controller (Output). When this difference exceeds Pos Delta Max for the amount of time specified by the Pos Delta Delay parameter, an alarm will be generated.

The Pos Feedback Reverse parameter is used to reverse the position feedback (Pos) from the recycle valve for applications in which the valve is reversed (where 0 corresponds to fully open and 1 corresponds to fully closed).

Air Miser For Air Miser applications, each Antisurge Controller used in the control system calculates a user flow (Q User), a recycle flow (Q Recycle), and a maximum flow (Q Max) which are passed to a Master Performance Controller. The Master Controller uses these inputs to determine when to turn off or turn on compressors in response to airflow requirements. Refer to UM 4104, Using the Series 4 Performance Controller AFM, for more information.

April 20, 1998


Maximum Flow The maximum flow (Q Max) is calculated as the maximum flow the compressor can deliver under current operating conditions:

Max Flow = CQ Max · fQ Max(pd)

where:

Max Flow = maximum available flow (Q Max)

CQ Max = max flow coefficient (Q Max Coefficient)

fQ Max(pd) = max flow characterizer (Q Max Characterizer), based on discharge pressure

If the Antisurge Controller Status is STOPPING or SHUTDOWN, or the Performance Controller is in Manual, the Antisurge Controller will report Q Max = Q User, thus indicating its throughput cannot be increased. Also, if the Load Sharing Performance Controller goes to a fallback PID control, the Antisurge Controller will set Q Max = Q User.

If the Antisurge Controller Status is RUN NEXT SD, it will report Q Max = 0 (zero).

The Status of the Load Sharing Performance Controller is obtained using the LS Status LTOP parameter. This includes the Next Stop information from the Load Sharing Controller, as well as information on whether the Load Sharing Controller is in a manual control or fallback condition.

User Flow andRecycle Flow

The user flow (Q User) is obtained by the Antisurge Controller using an actual net flow measurement, or is calculated by subtracting the recycle flow (Q Recycle) from the mass flow through the compressor, as illustrated in Figure 3-16.

Figure 3-16 User and Recycle Flows

Compressor

Mass Flow

Recycle Flow

User Flow(Q User)

(Q Recycle)



If a net flow rate measurement is available, the Net Flow Available parameter should be set On. Q User will then be calculated from the mass flow formula:

where:

Q User = user flow (Q User)

CQ User = user flow coefficient (Q User Coefficient)




If no net flow measurement is available, the Net Flow Available parameter should be set Off. The user flow (Q User) will then be calculated by subtracting an estimated recycle flow rate (Q Recycle) from the mass flow (Flow):

where:

Q User = user flow (Q User)

Flow = mass flow (Flow)

Q Rec = recycle flow (Q Recycle)

CQ User = user flow coefficient (Q User Coefficient)

fQ Rec(Out) = recycle flow output characterizer (Q Rec Out Characterizer)

fQ Rec(Rc) = recycle flow compression ratio characterizer (Q Rec Rc Characterizer)



Q User CQ User

∆po po⋅To

--------------------⋅=

Q User Flow Q Recycle–=

Q User Flow CQ User fQ Rec(Out) fQ Rec(Rc)pd

Td

----------⋅ ⋅ ⋅–=

April 20, 1998


Note: When specifying the value of C Q User , the flow-scaling coefficient (Q User Coefficient), the user must calculate a value consistent with the pressure and temperature units used in the equation.

AntichokeControl

For applications which require protection against reaching a choked-flow condition through the compressor, the Series 4 Antisurge Controller can be configured to operate as an Antichoke Controller by setting the Antichoke Enable parameter to On. The Controller Type parameter will indicate that the controller is operating as an Antichoke Controller.

As shown in Figure 3-17, an additional Antisurge Controller (UIC2) is used to control an antichoke valve located in the discharge of the compressor. When the flow through the compressor is safely below a choked condition, the antichoke valve remains open. As the flow approaches a choked condition, the Antichoke Controller begins closing the valve to reduce the flow through the compressor.

Figure 3-17 Simplified Antichoke Controller Configuration

The Antichoke Controller communicates its control actions to the Performance and Antisurge Controllers to allow them to coordinate their control actions.

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In multicompressor applications, one Antichoke Controller is typically used per machine.

As with the antisurge control function, the antichoke function uses a number of control lines to determine its control responses and actions. Two of these antichoke control lines are shown on the compressor map in Figure 3-18.

Figure 3-18 Antichoke Control Lines

A Choke Limit Line is established within the controller based on data for each specific compressor application. The flow through the compressor will be choked whenever the operating point of the compressor reaches the Choke Limit Line, or passes into the choked flow region of the compressor map.

To prevent the compressor from reaching a choked flow condition, a Choke Control Line is also established within the controller. When the operating point reaches the Choke Control Line, the controller will begin to close the antichoke valve to reduce the flow through the compressor. The Safety Margin (b), which is the distance between the Choke Control and Choke Limit Lines, is calculated in the same manner as it is for the antisurge control function (see page 3-10).

An Antichoke Controller uses the same parameters, control algorithms, and control functions to configure and calculate the antichoke control response that are used for the antisurge control response. The only difference is that the Antichoke

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ontro

l Lin

e

Choke Contro

l Line

Choke Limit Line

Flow

}Antisurge Control Lines }Antichoke Control Lines

Safety Margin, b

0

Safety Margin, b

April 20, 1998


Controller inverts the numerator and denominator modes in the calculation of the proximity-to-surge variable, Ss, which would now more appropriately be called the proximity-to-choke variable (see Numerator and Denominator Modes on page 3-3). In this way, the deviation between the operating point and the control line will decrease as the operating point moves to the right toward the Choke Control Line, instead of to the left toward the Surge Control Line, as in antisurge control.

In addition, the redundant transmitter signal-selection logic in an Antichoke Controller is different than that in an Antisurge Controller, as summarized in Table 3-17.

Table 3-17 Signal Selection Logic for Antichoke Controller

Note: The limiting control loops should not be used in an Antichoke Controller.

The output features which apply to the antisurge output (output clamping, valve flow characterization, dead-band compensation, and output reverse) are also applied to the antichoke output.

Caution: The antichoke valve should be prevented from closing to the point that it induces compressor surge. The amount of valve closure can be limited using the valve output clamps (Output High Limit and Output Low Limit).

Transmitter Signal Signal Selection Logic

Antisurge Controller Antichoke Controller

delta pressure low select high select

discharge pressure high select low select

suction pressure higher Ss value higher Ss value

discharge temperature high select low select

suction temperature low select high select



OperatingStates

At any given time, the Antisurge Controller will be in one of the operating states summarized in Table 3-18.

Table 3-18 Antisurge Controller Operating States

The State parameter indicates the current operating state of the controller.

Figure 3-19 Operating States and Transitions

State Description

SHUTDOWN holds recycle valve fully open

IDLE ramps recycle valve fully open

PURGE ramps recycle valve fully closed

RUN modulates recycle valve to prevent surge and minimize recycling

MANUAL holds recycle valve in position specified by user

REMOTE RUN

for parallel valve sharing, modulates shared recycle valve to protect the compressor of another controller

STARTING closes recycle valve

Remote RunRun

Shutdown

Purge

Idle

1

14

7

17 8

4

9

10

11

1518

2 19

5

6

20

312

13

21

Starting

22

23

Manual

16

April 20, 1998


Transitions The Antisurge Controller selects its operating state based on the operating status of the compressor and various operating state requests. The operating state transitions are given in Figure 3-19 and Table 3-19.

Table 3-19 Operating State Transitions

StateTransitionNumber

Old State New State Events

1 Shutdown Purge Purge set to On and N < Idle Speed SP

2 Shutdown Manual Manual Auto set to Manual

3 Shutdown Remote Run Valve Sharing controller in Run state and Series set to Off

4 Idle Run Compressor running and Stop set to Off

5 Idle Shutdown ESD set to On or (Display Output at maximum clamp and N < Idle Speed SP)

6 Idle Manual Manual Auto set to Manual

7 Run Shutdown ESD set to On

8 Run Manual Manual Auto set to Manual

9 Run Idle Compressor not running or Stop set to On

10 Run Remote Run Valve Sharing controller in Run state, Series set to Off, and (ESD set to On or Stop set to On or compressor not running)

11 Remote Run Run All Valve Sharing controllers in Shutdown state, compressor running, Stop and ESD set to Off

12 Remote Run Shutdown All Valve Sharing controllers in Shutdown state and Stop or ESD set to On

13 Remote Run Manual Manual Auto set to Manual

14 Purge Idle Purge set to Off

15 Purge Manual Manual Auto set to Manual

16 Purge Run Compressor is running

17 Manual Run Compressor running and Manual Auto, Stop, and ESD set to Off

18 Manual Purge Manual Auto set to Auto, and Stop and Purge set to On

19 Manual Shutdown Manual Auto set to Auto, Purge set to Off, and Stop set to On

20 Manual Idle Manual Auto set to Auto, ESD set to Off and (compressor not running or Stop set to On)

21 Manual Remote Run Secondary Valve Sharing controller in Run state, Series and Manual Auto set to Auto, and Stop or ESD set to On

22 Shutdown Starting Stop and ESD set to Off, compressor running, and Deviation > Dev Threshold

23 Starting Run Deviation < Dev Threshold, or in limit, or in POC, or Output at low clamp, or failed analog input transmitter



Shutdown State In the Shutdown state, the controller holds the recycle valve fully open (Display Output is held at its maximum clamp) so that any high-pressure gas leaking through the check valve can flow around the compressor. This prevents surge while the compressor is idling and protects against reverse flow when the compressor is stopped.

The Stop Enable parameter must be set to On for the controller to enter the Shutdown state.

The Antisurge Controller enters the Shutdown state when a Stop or ESD request is set, or at the conclusion of the Idle state ramping function, unless:

■ a Purge request is also asserted and the Purge Enable parameter is set to On, in which case the controller momentarily enters the Shutdown state before entering the Purge state;

■ a Manual request is also asserted and the Shutdown Manual Enable parameter is set to On, in which case the Manual state is selected; or

■ any secondary Valve Sharing Controller is running (see criteria in Automatic Sequencing on page 3-91) and the Series parameter within the primary Valve Sharing Controller is Off, in which case the Remote Run state is selected for the primary controller.

The Shutdown state can also be requested by any secondary Valve Sharing Controller that is not running (see criteria in Automatic Sequencing on page 3-91), provided the Series parameter within the primary controller is set to On.

All Stop and ESD requests must be cleared before the controller can enter the Run state.

The Stop Status parameter is set to On when the Antisurge Controller has been stopped using the Stop parameter or the Stop digital input. Stop Status is used to allow other controllers to get the condition of the Antisurge Controller directly from this value.

Likewise, the ESD Status parameter is set to On when the Antisurge Controller has been stopped using the ESD parameter or the ESD digital input. ESD Status is used to allow other controllers to get the condition of the Antisurge Controller directly from this value.

April 20, 1998


Idle State The Antisurge Controller enters the Idle state when a Stop request is received (the Stop digital input is set to 1, or the Stop parameter is set to On), or when the compressor shuts down. The purpose of this operating state is to ramp the recycle valve fully open while the compressor shuts down.

The Stop Enable parameter must be set to On, and the ESD and manual requests must be cleared for the controller to enter the Idle state.

The Idle state can also be requested by any secondary Valve Sharing Controller that is not running (see criteria in Automatic Sequencing on page 3-91), provided the Series parameter within the primary controller is set to On.

All such requests must be cleared before the controller can enter the Run state.

When the controller enters the Idle state, it will increase the Display Output at the ramp rate specified by the Stop Rate parameter until it reaches the maximum clamp (Output High Limit), thus fully opening the recycle valve. The controller will then automatically switch to the Shutdown state. It will immediately transfer to the Shutdown state if an ESD request is set during this ramp. The Recycle Trip response will remain active during this ramp, and will trigger step increases in the recycle rate if the operating point reaches the Recycle Trip Line.

The controller will return to the Run state if the condition that triggered the shutdown is cleared before the resulting ramp terminates (such as clearing the Stop request while the compressor is still running, or restarting the compressor while Stop is cleared).

The Idle Speed SP parameter is used to specify the idle speed set point for the Antisurge Controller while it is in the Idle state (Running = No). When the speed of the compressor (N) is above this set point, a purge of the compressor is prohibited and surge protection is still active. The controller cannot enter the Purge state until N is below the Idle Speed SP.

Purge State The Antisurge Controller transfers from the Shutdown state to the Purge state when the compressor is purged. When the Purge state is selected, the controller will fully close the recycle valve by ramping the Display Output to zero at the rate specified by the Purge Rate parameter. The controller



will then hold the recycle valve fully closed so purge gas can be forced through the compressor.

The Purge Enable and Stop Enable parameters must be set to On and the controller must be in the Shutdown state for the controller to enter the Purge state when the Purge request is set.

The Purge state can be requested by:

■ setting the Purge digital input;

■ setting the Purge parameter; or

■ any secondary Valve Sharing Controller that is in the Purge state, provided the Series parameter for the primary Valve Sharing Controller is set to On.

All such requests must be cleared before the controller can transfer to the Idle state.

Clearing the purge request by setting the Purge parameter to Off will transfer the controller to the Idle state and ramp the recycle valve toward the High Clamp.

The Controller will transfer from the Purge state to the Run state when the compressor running criteria is met (see Automatic Sequencing on page 3-91).

Starting State The Antisurge Controller will transfer from the Shutdown state to the Starting state when the Stop and ESD requests are cleared and the compressor running criteria is met (see Automatic Sequencing on page 3-91).

When the controller enters the Starting state, the recycle valve is closed at the rate specified by the Start Rate parameter.

The controller will then transfer from the Starting state to the Run state when any of the following events occur:

■ Deviation < Dev Threshold,■ the Output reaches the Low Clamp,■ a limit condition occurs (Limit is On),

■ a Pressure Override Control response occurs (POC is On), or

■ an analog input transmitter fails.

April 20, 1998


Run State The Antisurge Controller operates in the Run state when the compressor is running (see criteria in Automatic Sequencing on page 3-91) and there are no active ESD, Stop, or Manual requests.

In the Run state, the controller modulates the recycle valve as needed to protect the compressor against surge, using the control responses described in this chapter.

Manual State The Manual state allows the user to manually control the position of the recycle valve. This state is selected whenever the Manual Auto parameter is set to On, provided that:

■ the compressor is running or, if not running, the Shutdown Manual Enable parameter is set to On, and

■ the operating point is to the right of the Recycle Trip Line, or, if to the left of the RTL, the Manual Override parameter is set to On or any MOR digital input is set.

The Manual Auto parameter can be set by setting any Manual discrete input, cleared by asserting any Auto input, or toggled by asserting the Manual Auto parameter. The Auto/Man control key on the Operator Interface Module (OIM) can also be used to toggle between the automatic and manual modes of operation. The Manual Auto parameter can be directly set or cleared using computer communications.

If the Shutdown Manual Enable parameter is set to Off, the Manual state can be selected only when the controller is in the Starting, Run, or Remote Run states. The controller will then revert to automatic operation if the compressor is subsequently shut down. When Shutdown Manual Enable is On, the user can manually manipulate the valve in the Shutdown state.

In the Manual state, the Manual Target parameter is used to set the manual output of the Antisurge Controller. This parameter can be set by serial communications or varied by a numeric input. The Manual Target increases at the Manual Rate Open, and decreases at the Manual Rate Close.

The Up and Down parameters can be set and cleared by the Up and Down digital inputs, by the Up and Down control keys on the OIM, or using serial communications.



In the Manual state, the Display Output tracks the value of the Manual Target parameter:

■ The Display Output increases at the Manual Rate Open if it is below the Manual Target.

■ The Display Output decreases at the Manual Rate Close if it is greater than the Manual Target.

If the Manual Override parameter is set to Off and no MOR inputs are asserted, automatic control is restored when a Recycle Trip occurs. This prevents a user from accidentally inducing surge by closing the recycle valve too far or by inadvertently leaving the controller in Manual. Automatic control is also restored if an ESD or Stop request is set.

If Manual Override is set to On or the MOR digital input is set, the user can manually override these features and adjust the Manual Target to any value, even if it causes the compressor to surge. When Manual Override is enabled, the Hard Manual digital output will be set to On, whether the controller is in automatic or manual operation. Setting a Stop or ESD request while Manual Override is enabled will cause the controller to go to Manual Shutdown, in which the Recycle Trip function is inactive.

Warning! Enabling the Manual Override parameter is not recommended because it leaves the compressor unprotected from surge.

When the Antisurge Controller is in manual, the Manual LED on the Operator Interface Module (OIM) will be On continuously. However, when the controller is in manual and the manual override function is active, the Manual LED will blink.

Note: When the controller is in automatic operation, there is no LED indication that the manual override function is active.

April 20, 1998


Remote RunState

The Antisurge Controller operates in the Remote Run state when its compressor is shut down (or a Stop or ESD request is set), but its recycle valve is being modulated by a valve-sharing companion controller for a parallel compressor in the Run state. Only a primary Valve Sharing controller can operate in the Remote Run state.

This state allows the operation of some of the compressors in a parallel arrangement while the others are shut down. The Series parameter for this Antisurge Controller must be set to Off.

The Remote Run state is essentially identical to the Run state except that the controller does not calculate an antisurge or limiting dCV for its own compressor. The new value for CV Total is computed by selecting the highest of only the Pressure Override Control, Recycle Balancing, and Valve Sharing dCVs, then adding the Loop Decoupling and Load Sharing dCVs.

AutomaticSequencing

In the Run state, the controller modulates the antisurge valve as needed to protect the compressor from surge.

A normal shutdown is initiated whenever the compressor is shut down or a Stop request is set. The recycle valve is then ramped open at the rate specified by the Stop Rate parameter until it reaches its output high clamp (Output High Limit). If the rate is set to zero, the valve will open immediately to the high clamp position. The valve will also immediately open if the operating point of the compressor moves to the left of the Recycle Trip Line while the compressor is being stopped.

While the compressor is shut down, the controller holds the antisurge valve at the high output clamp position.

During start-up, the antisurge valve is ramped from the high output clamp position to the fully closed position at the rate specified by the Start Rate parameter.



The Antisurge Controller determines if the compressor is running by comparing the following process variables to the indicated thresholds:

■ discharge pressure (Pd) is compared to the value specified by the Minimum Pressure parameter;

■ main flow measurement (∆po) is compared to the value specified by the Minimum Flow parameter; and

■ rotational speed (N) is compared to the value specified by the Minimum Speed parameter.

The compressor is assumed to be running if all of these variables have exceeded their thresholds for the number of seconds specified by the Startup Time parameter. It is assumed to be shut down if any one of them falls below its threshold for the number of seconds specified by the Stop Time.

The Running parameter indicates the compressor run status.

The Not Running parameter is set to On when the Antisurge Controller is shut down. It can be used by other controllers as a stop input (through the configuration of the Digital Inputs (2) LTOP array).

Any variable assigned to a failed input is assumed to be above its threshold. Thus, the compressor is assumed to be running unless a valid input indicates otherwise. The failure of an input will not cause Running to change to On or Off. The controller will remain in its current operating condition. However, an input failure could also trigger a fallback strategy (see Fallback Strategies on page 3-27).

April 20, 1998

Parameter Descriptions 4-1

Chapter 4: Parameter Descriptions

The Antisurge Controller has two groups of database parameters:

■ System Parameters are related to the AFM hardware, operating systems, and other functions that are common to all applications running on the same IOM as the Antisurge Controller. While these parameters are not a part of the antisurge control application software, many affect the operation of the Antisurge Controller.

■ Application Parameters, as the name implies, are those database parameters directly related to the execution of the antisurge control application software. Some are used for configuration of the controller, others indicate controller status, and others are used for on-line operation of the controller.

Further description of the System parameters can be found in UM4003, Series 4 Fault Tolerant Operating System. Additional descriptions of the Application parameters, and a complete list of those parameters, are contained in the remainder of this chapter.

Warning! The user must verify that each system and application parameter is set to the correct value before placing the Antisurge Controller into operation.

ParameterData Types

There are three types of application parameters in the Antisurge Controller:

■ Binary (sometimes called Bit, Digital, or Discrete)

■ Integer

■ Floating-Point

Additional information on each parameter type is presented in the following sections.


4-2 Parameter Descriptions

BinaryParameters

Each binary parameter has only two possible values, logic 0 or logic 1. The state of the parameter when it is set to a value of zero (logic low) or to a value of one (logic high) is listed in the table.

IntegerParameters

Integers are 32-bit data words. Some integer parameters are used to represent whole numbers, while others are packed arrays of bit data.

Floating-PointParameters

Many of the Antisurge Controller’s parameters are floating-point numbers. Floating-point numbers are used for virtually all numbers involved in calculations because of their high degree of resolution. (Series 4 floating-point numbers conform to IEEE standards.)

Because of the large span of floating-point numbers, which exceeds the range needed for real-world control problems, the valid range for each parameter is established based on reasonable process limits. The high and low limit for each parameter is listed in the parameter table.

ParameterTable

Table 4-1 on page 4-4 lists the Parameter Names for the Antisurge Controller parameters in alphabetical order. Tables containing cross-references between the Parameter Name and the Symbol Name are provided in Appendix A. Detailed descriptions of each application parameter are given beginning on page 4-15.

Note: Parameters in the TEST group are generally not described, because they are intended for use only by Compressor Controls Corporation personnel.

The following information is given in Table 4-1:

Parameter Name (OIM): The name of the parameter as it appears on the OIM and in the Configurator module of the OIS software package.

Group and Subgroup: Functional group and subgroup of the parameters as found in Configurator.

Engineering Units: The unit of measure, if any, for the parameter. Series 4 uses SI units for all parameters other than percentages.

April 20, 1998


Data Type: Floating point (FLT), Integer (INT), or Discrete (BIT).

Display Type: Used by the OIM and Configurator to format the display of the parameter data.

High/Low Limits or ON/OFF Values: The valid range for each floating-point or integer parameter based on reasonable process limits, or the state of the discrete parameter when it is set to a value of zero (logic low) or to a value of one (logic high).

Data Access Level: The write access level of the parameter consists of System, Engineer (ENGR), Supervisor (SPRV), or Operator (OPER) levels.

SYSTEM is the highest access level, which allows the user to set any database parameter and to execute any action that can be initiated by setting a parameter.

The ENGINEER access level allows the user to set any parameter that does not require SYSTEM access.

The SUPERVISOR access level allows the user to set only Supervisor or Operator level parameters.

The OPERATOR is the lowest access level and allows the user to set only Operator level parameters.

If no access level is listed, the parameter is a read-only parameter.

Note: An external supervisory control system communicating serially with the Antisurge Controller will have an ENGINEER access level.

Offset Address: The offset address of the parameter used in assigning the appropriate input or output within the LTOP arrays to the parameter.



Table 4-1 Antisurge Controller Parameters (Alphabetical)

Parameter Name Group Subgroup Eng. Units

Data Type

Display Type

Low Limit or 0 (Off) Value

High Limit or 1 (On) Value

Data Access Level

Offset Address

ALARM OPERATOR BIT BIT off on 109

ALARM BUFFER ALARM ALARM INT LIST 0 0 2

ALARM RESET ALARM ALARM BIT BIT off on OPER 1

ALPHA IN OUT FLT FLT 0 0 90

ALPHA OFFSET SPAN AND OFFSET

OFFSET FLT FLT 0 0 ENGR 422

ALPHA SPAN SPAN AND OFFSET

SPAN FLT FLT 0 0 ENGR 400

ALTERNATE K FALLBACK VALUE FLT FLT 0 100 ENGR 83

ALTERNATE K ENABLE FALLBACK ENABLE BIT BIT off on ENGR 37

ANALOG INPUTS *CONFIGURE IO LTOP IOINT LTOP 0 ENGR 1000

ANALOG OUTPUTS *CONFIGURE IO LTOP IOINT LTOP 0 ENGR 70

ANTICHOKE ENABLE CALCULATE SCL ANTICHOKE BIT BIT off on ENGR 178

ANTISURGE STATUS STATUS STATUS INT PACKET 0 0 600

ANTISURGE STATUS LTOP

*VS & CR VS INT LTOP 0 ENGR 550

APP NAME OIM NAMES BYTE BYTE 0 0 ENGR 0

APP SHORT NAME OIM NAMES BYTE BYTE 0 0 ENGR 20

B OPERATOR FLT FLT 0 0 115

BETA 3 LOAD SHARE LS FLT FLT 0 2 ENGR 140

BETA 5 CONFIGURE IO FLOW FLT FLT 0 1 ENGR 141

CONFIG SHOW GROUP *CONFIG DISPLAY INT INDEX 0 1 SYST 500

CONTROL OVERRIDE OPERATOR BIT BIT off on 115

CONTROL OVERRIDE SP STATUS STATUS % FLT FLT 0 1 OPER 189

CONTROLLER STATUS OPERATOR INT LIST 0 0 291

CONTROLLER TYPE STATUS STATUS INT LIST 0 0 297

CURRENT DCV OPERATOR INT LIST 0 0 292

CV STATUS STATUS % FLT FLT 0 0 180

CV TOTAL STATUS STATUS % FLT FLT 0 0 186

DCV TEST DCV FLT FLT 0 0 187

DECOUPLE CV LTOP *LOOP DECOUPLE

LD INT LTOP 0 ENGR 540

DEFAULT ADJACENT FLOW ENABLE

FALLBACK ENABLE BIT BIT off on ENGR 30

DEFAULT ADJACENT FLOW RATE

FALLBACK VALUE kPa1 FLT FLT 0 50000 ENGR 81

DEFAULT ALPHA FALLBACK VALUE FLT FLT 0 100 ENGR 80

DEFAULT ALPHA ENABLE


DEFAULT OUTPUT FALLBACK VALUE % FLT FLT 0 1 ENGR 85

DEFAULT PS FALLBACK VALUE kPa2 FLT FLT 0 20000 ENGR 88

DEFAULT PS ENABLE FALLBACK ENABLE BIT BIT off on ENGR 40

DEFAULT RC FALLBACK VALUE FLT FLT 0 100 ENGR 86

DEFAULT RC ENABLE FALLBACK ENABLE BIT BIT off on ENGR 34

DEFAULT SIGMA FALLBACK VALUE FLT FLT 0 10 ENGR 87

April 20, 1998


DEFAULT SIGMA ENABLE


DEFAULT SPEED FALLBACK VALUE rpm FLT FLT 0 50000 ENGR 84

DEFAULT SPEED ENABLE


DENOMINATOR TEST TEST FLT FLT 0 0 397

DENOMINATOR MODE CALCULATE SCL CALC MODES

INT LIST 0 4095 ENGR 352

DERIVATIVE RESPONSE DB

CONTROL DERIV RESPONSE

% FLT FLT 0 1 ENGR 373

DERIVATIVE RESPONSE ENABLE


BIT BIT off on ENGR 140

DERIVATIVE RESPONSE MAX



DERIVATIVE RESPONSE RATE


%/s FLT FLT 0 1 ENGR 371

DERIVATIVE RESPONSE TC


s FLT FLT 0 100 ENGR 372

DEV THRESHOLD AUTO SEQUENCE START FLT FLT 0 0 ENGR 3

DEVIATION OPERATOR FLT FLT 0 0 181

DIGITAL INPUTS *CONFIGURE IO LTOP IOINT LTOP 0 ENGR 132

DIGITAL INPUTS *CONFIGURE IO LTOP IOINT LTOP 0 ENGR 156

DIGITAL OUTPUTS *CONFIGURE IO LTOP IOINT LTOP 0 ENGR 1100

DISPLAY OUTPUT OPERATOR % FLT FLT 0 0 185

DOWN OPERATOR INT INT 0 0 OPER 93

DPC IN OUT kPa FLT FLT 0 0 91

DPC OFFSET SPAN AND OFFSET

OFFSET kPa FLT FLT 0 0 ENGR 426

DPC SPAN SPAN AND OFFSET

SPAN kPa* FLT FLT 0 0 ENGR 404

DPO CALC IN OUT kPa1 FLT FLT 0 0 148

DPO COMP IN OUT kPa1 FLT FLT 0 0 116

DPO DEV IN OUT BIT BIT off on 117

DPO DIFFERENTIAL THRESHOLD

CONFIGURE IO ANALOG IN kPa1 FLT FLT 0 0 ENGR 12

DPO RATE SO & RT EAS kPa1/s FLT FLT 0 0 ENGR 220

DPO SAMPLES SO & RT EAS INT LIST 0 0 ENGR 331

DPO SELECT IN OUT INT LIST 0 0 305

DPO SIDE IN OUT kPa1 FLT FLT 0 0 99

DPO SIDE OFFSET SPAN AND OFFSET

OFFSET kPa1 FLT FLT 0 0 ENGR 420

DPO SIDE SPAN SPAN AND OFFSET

SPAN kPa1* FLT FLT 0 0 ENGR 412

DPO USED IN OUT kPa1 FLT FLT 0 0 118

DPO1 IN OUT kPa1 FLT FLT 0 0 93

DPO1 OFFSET SPAN AND OFFSET


DPO1 SPAN SPAN AND OFFSET


DPO2 IN OUT kPa1 FLT FLT 0 0 117


Data Type

Display Type



Data Access Level

Offset Address



DPO2 OFFSET SPAN AND OFFSET


DPO2 SPAN SPAN AND OFFSET


DPOS MODE CALCULATE SCL CALC MODES


DPRESSURE EU ENGINEERING UNITS

ENG UNITS kPa1 INT INT 0 0 ENGR 233

DPRESSURE RATE EU ENGINEERING UNITS

ENG UNITS kPa1/s INT INT 0 0 ENGR 238

DPRESSURE2 EU ENGINEERING UNITS

ENG UNITS kPa1* INT INT 0 0 ENGR 236

DSS IN OUT FLT FLT 0 0 78

DSS MAX IN OUT FLT FLT 0 0 OPER 79

DTC IN OUT K FLT FLT 0 0 92

DTC OFFSET SPAN AND OFFSET

OFFSET K FLT FLT 0 0 ENGR 427

DTC SPAN SPAN AND OFFSET

SPAN K* FLT FLT 0 0 ENGR 405

EAS OPERATOR BIT BIT off on 50

EAS MODE SO & RT EAS INT LIST 0 0 ENGR 330

ESD OPERATOR BIT BIT off on OPER 104

ESD STATUS STATUS STATUS BIT BIT off on 163

EXC SURGE STATUS STATUS BIT BIT off on 172

F1 CHARACTERIZER CALCULATE SCL CHARAC-TERIZERS

FLT GRAPH 0 0 ENGR 240

F1 CHARACTERIZER MODE

CALCULATE SCL CHAR MODES





















FALLBACK OPERATOR BIT BIT off on 111

FILTERED POC VALID POC POC BIT BIT off on 118

FLOW IN OUT kg/s FLT FLT 0 0 119

FLOW CHANNEL CONFIGURE IO FLOW INT LIST 0 4095 ENGR 95

FLOW COEFFICIENT CONFIGURE IO FLOW FLT FLT 0 0 ENGR 145

FLOW EU ENGINEERING UNITS

ENG UNITS kg/s INT INT 0 10 ENGR 241


Data Type

Display Type



Data Access Level

Offset Address

April 20, 1998


FLOW OFFSET SPAN AND OFFSET

OFFSET kg/s FLT FLT 0 0 ENGR 435

FLOW SIDESTREAM COEFFICIENT 1

SIDE STREAM SS FLT FLT 0 0 ENGR 390





FLOW SPAN SPAN AND OFFSET

SPAN kg/s FLT FLT 0 0 ENGR 418

FLOW->PRESSURE TIME LAG

SO & RT EAS s FLT FLT 0 2 ENGR 221

FT ALARM LEVEL ALARM FT ALARM INT INDEX 0 0 ENGR 420

FT ALARM RESET ALARM FT ALARM BIT BIT off on OPER 2

GEAR RATIO CONFIGURE IO ANALOG IN FLT FLT 0 4 ENGR 13

HIGH CLAMP STATUS STATUS BIT BIT no yes 112

HISTORY BUFFER ALARM HISTORY INT LIST 0 0 22

HISTORY RESET ALARM HISTORY BIT BIT off on SPRV 0

HP IN OUT FLT FLT 0 0 94

I OFFSET *VS & CR CR FLT FLT 0 0 ENGR 443

IDLE SPEED SP AUTO SEQUENCE START rpm FLT FLT 0 0 ENGR 14

K CALCULATE SCL SO FLT FLT 0 200 ENGR 393

K PRIME TEST TEST FLT FLT 0 0 398

KI ADJUST CONTROL PID s FLT FLT 1 100 ENGR 213

KW IN OUT kW FLT FLT 0 0 95

KW OFFSET SPAN AND OFFSET

OFFSET kW FLT FLT 0 0 ENGR 430

KW SPAN SPAN AND OFFSET

SPAN kW FLT FLT 0 0 ENGR 408

LD COMPANIONS LOOP DECOUPLE LD INT PACKET 0 0 ENGR 270

LD COMPANIONS COEFFICIENT

LOOP DECOUPLE LD FLT FLT 0 0 ENGR 150

LD STATUS STATUS STATUS INT PACKET 0 0 610

LD STATUS LTOP *LOOP DECOUPLE

LD INT LTOP 0 ENGR 530

LD VALID STATUS STATUS BIT BIT off on 58

LIMIT OPERATOR BIT BIT off on 110

LOAD SHARE GAIN LOAD SHARE LS FLT FLT 0 0 ENGR 142

LOW CLAMP STATUS STATUS BIT BIT no yes 113

LS STATUS STATUS STATUS INT PACKET 0 0 499

LS STATUS LTOP *AIR MISER AM INT LTOP 0 ENGR 406

MANUAL AUTO OPERATOR BIT BIT man auto OPER 100

MANUAL FALLBACK ENABLE


MANUAL OVERRIDE CONTROL MANUAL BIT BIT off on ENGR 90

MANUAL RATE CLOSE CONTROL MANUAL %/s FLT FLT 0 1 ENGR 171

MANUAL RATE OPEN CONTROL MANUAL %/s FLT FLT 0 1 ENGR 170

MANUAL TARGET OPERATOR % FLT FLT 0 1 OPER 188

MASTER CONTROLLERS MASTER INT PACKET 0 0 ENGR 290


Data Type

Display Type



Data Access Level

Offset Address



MASTER B ENABLE SO & RT SO BIT BIT off on ENGR 175

MASTER B LTOP *SO & RT SO INT LTOP 0 ENGR 390

MASTER CV LTOP *LOAD SHARE LS INT LTOP 0 ENGR 490

MASTER STATUS STATUS STATUS INT PACKET 0 0 494

MASTER STATUS LTOP *LOAD SHARE MASTER INT LTOP 0 ENGR 495

MAX +DPD SO & RT EAS kPa/s FLT FLT 0 0 OPER 111

MAX +DPO SO & RT EAS kPa1/s FLT FLT 0 0 OPER 109

MAX -DPD SO & RT EAS kPa/s FLT FLT 0 0 OPER 112

MAX -DPO SO & RT EAS kPa1/s FLT FLT 0 0 OPER 110

MINIMUM FLOW AUTO SEQUENCE START kPa1 FLT FLT 0 0 ENGR 0

MINIMUM FLOW CONTROL ENABLE


MINIMUM FLOW SETPOINT

FALLBACK VALUE kPa1 FLT FLT 0 50000 ENGR 82

MINIMUM PRESSURE AUTO SEQUENCE START kPa FLT FLT 0 0 ENGR 2

MINIMUM SPEED AUTO SEQUENCE START rpm FLT FLT 0 0 ENGR 1

N IN OUT rpm FLT FLT 0 0 96

N OFFSET SPAN AND OFFSET

OFFSET rpm FLT FLT 0 0 ENGR 431

N SPAN SPAN AND OFFSET

SPAN rpm FLT FLT 0 0 ENGR 409

NET FLOW AVAILABLE AIR MISER AM BIT BIT off on ENGR 177

NOT RUNNING STATUS STATUS BIT BIT off on 65

NUMERATOR TEST TEST FLT FLT 0 0 396

NUMERATOR MODE CALCULATE SCL CALC MODES


OUTPUT STATUS STATUS % FLT FLT 0 0 184

OUTPUT HIGH LIMIT CONFIGURE IO CONTROL VALVE


OUTPUT LOW LIMIT CONFIGURE IO CONTROL VALVE


OUTPUT REVERSE CONFIGURE IO CONTROL VALVE

BIT BIT norM rev ENGR 10

OUTPUT TRACKING RATE

CONFIGURE IO ANALOG OUT

1/min FLT FLT 0 0 ENGR 201

P OFFSET *VS & CR CR % FLT FLT 0 0 ENGR 442

PD IN OUT kPa FLT FLT 0 0 97

PD DGO SWITCH LEVEL CONFIGURE IO DIGITAL OUT

kPa* FLT FLT 0 0 ENGR 439

PD LIMIT ENABLE LIMIT CONTROL PD BIT BIT off on ENGR 61

PD LIMIT SP LIMIT CONTROL PD kPa FLT FLT 0 20000 ENGR 135

PD LIMIT SP DEFAULT LIMIT CONTROL PD kPa FLT FLT 0 20000 ENGR 137

PD LIMIT STATUS STATUS STATUS INT LIST 0 0 293

PD OFFSET SPAN AND OFFSET


PD PID DZ LIMIT CONTROL PD FLT FLT 0 100 ENGR 136

PD PID KD LIMIT CONTROL PD s FLT FLT 0 64 ENGR 132

PD PID KI LIMIT CONTROL PD 1/min FLT FLT 0 128 ENGR 133

PD PID KP LIMIT CONTROL PD FLT FLT 0 128 ENGR 134


Data Type

Display Type



Data Access Level

Offset Address

April 20, 1998


PD PID TF LIMIT CONTROL PD FLT FLT 0 100 ENGR 192

PD RATE SO & RT EAS kPa/s FLT FLT 0 0 ENGR 223

PD SAMPLES SO & RT EAS INT LIST 0 0 ENGR 332

PD SPAN SPAN AND OFFSET


PID VELOCITY HIGH LIMIT

CONTROL PID % FLT FLT 0 50 ENGR 380

PID VELOCITY LOW LIMIT

CONTROL PID % FLT FLT -50 0 ENGR 381

PIS IN OUT kPa FLT FLT 0 0 230

PIS OFFSET SPAN AND OFFSET


PIS SPAN SPAN AND OFFSET


POC OPERATOR BIT BIT off on 55

POC CV POC POC FLT FLT 0 0 447

POC CV LTOP *POC POC INT LTOP 0 ENGR 492

POC DCV POC POC FLT FLT 0 0 448

POC ENABLE POC POC BIT BIT off on ENGR 70

POC FILTERED DELTA POC POC kPa* FLT FLT 0 0 449

POC FILTERED DELTA MAX

POC POC kPa* FLT FLT 0 0 OPER 450

POC FILTERED GAIN POC POC FLT FLT 0 1000 ENGR 445

POC FILTERED THRESHOLD

POC POC kPa* FLT FLT 0 1000 ENGR 444

POC PV TF POC POC s FLT FLT 0 100 ENGR 446

POC STATUS STATUS STATUS INT LIST 0 0 296

POS IN OUT % FLT FLT 0 0 182

POS DELTA DELAY CONFIGURE IO CONTROL VALVE

s FLT FLT 0 0 ENGR 144

POS DELTA MAX CONFIGURE IO CONTROL VALVE


POS FEEDBACK REVERSE

CONFIGURE IO CONTROL VALVE

BIT BIT norM rev ENGR 11

POWER EU ENGINEERING UNITS

ENG UNITS kW INT INT 0 0 ENGR 232

PRESSURE CHANNEL CONFIGURE IO FLOW INT LIST 0 4095 ENGR 96

PRESSURE EU ENGINEERING UNITS

ENG UNITS kPa INT INT 0 0 ENGR 231

PRESSURE RATE EU ENGINEERING UNITS

ENG UNITS kPa/s INT INT 0 0 ENGR 237

PRESSURE->FLOW TIME LAG

SO & RT EAS s FLT FLT 0 2 ENGR 222

PRESSURE2 EU ENGINEERING UNITS

ENG UNITS kPa* INT INT 0 0 ENGR 235

PS IN OUT kPa2 FLT FLT 0 0 98

PS DGO SWITCH LEVEL CONFIGURE IO DIGITAL OUT

kPa2* FLT FLT 0 0 ENGR 440

PS LIMIT ENABLE LIMIT CONTROL PS BIT BIT off on ENGR 60

PS LIMIT PV LIMIT CONTROL PS kPa2 FLT FLT 0 0 138


Data Type

Display Type



Data Access Level

Offset Address



PS LIMIT SP LIMIT CONTROL PS kPa2 FLT FLT 0 10000 ENGR 125

PS LIMIT SP DEFAULT LIMIT CONTROL PS kPa2 FLT FLT 0 10000 ENGR 127

PS LIMIT STATUS STATUS STATUS INT LIST 0 0 294

PS OFFSET SPAN AND OFFSET


PS PID DZ LIMIT CONTROL PS FLT FLT 0 100 ENGR 126

PS PID KD LIMIT CONTROL PS s FLT FLT 0 64 ENGR 122

PS PID KI LIMIT CONTROL PS 1/min FLT FLT 0 128 ENGR 123

PS PID KP LIMIT CONTROL PS FLT FLT 0 128 ENGR 124

PS PID TF LIMIT CONTROL PD FLT FLT 0 100 ENGR 193

PS SPAN SPAN AND OFFSET


PURGE OPERATOR BIT BIT off on OPER 105

PURGE ENABLE AUTO SEQUENCE STOP BIT BIT off on ENGR 161

PURGE RATE AUTO SEQUENCE STOP 1/min FLT FLT 0 1000 ENGR 8

PVI IN OUT kPa FLT FLT 0 0 114

PVI OFFSET SPAN AND OFFSET


PVI SPAN SPAN AND OFFSET


Q MAX IN OUT kg/s FLT FLT 0 0 481

Q MAX CHARACTERIZER

AIR MISER AM FLT GRAPH 0 0 ENGR 490

Q MAX COEFFICIENT AIR MISER AM FLT FLT 0 0 ENGR 488

Q REC OUT CHARACTERIZER


Q REC RC CHARACTERIZER


Q RECYCLE IN OUT kg/s FLT FLT 0 0 479

Q USER IN OUT kg/s FLT FLT 0 0 480

Q USER COEFFICIENT AIR MISER AM FLT FLT 0 0 ENGR 489

R IN OUT FLT FLT 0 0 100

RB COMPANIONS RECYCLE BALANCE

RB INT PACKET 0 0 ENGR 310

RB CV LTOP *RECYCLE BALANCE

RB INT LTOP 0 ENGR 470

RB RATE RECYCLE BALANCE

RB 1/min FLT FLT 0 0 ENGR 200

RB VALID STATUS STATUS BIT BIT off on 57

RB VALID LTOP *RECYCLE BALANCE

RB INT LTOP 0 ENGR 480

RC IN OUT FLT FLT 0 0 101

RC LIMIT ENABLE LIMIT CONTROL RC BIT BIT off on ENGR 62

RC LIMIT SP LIMIT CONTROL RC FLT FLT 0 10000 ENGR 190

RC LIMIT SP DEFAULT LIMIT CONTROL RC FLT FLT 0 10000 ENGR 191

RC LIMIT STATUS STATUS STATUS INT LIST 0 0 295

RC PID DZ LIMIT CONTROL RC FLT FLT 0 100 ENGR 198

RC PID KD LIMIT CONTROL RC s FLT FLT 0 64 ENGR 194

RC PID KI LIMIT CONTROL RC 1/min FLT FLT 0 128 ENGR 195


Data Type

Display Type



Data Access Level

Offset Address

April 20, 1998


RC PID KP LIMIT CONTROL RC FLT FLT 0 128 ENGR 196

RC PID TF LIMIT CONTROL PD FLT FLT 0 100 ENGR 197

RC SPAN SPAN AND OFFSET


RECYCLE TRIP TEST TEST TEST BIT BIT off on ENGR 106

REMOTE LOW CLAMPING

STATUS STATUS BIT BIT off on 116

RT OPERATOR BIT BIT off on 51

RT COUNT #OPERATOR INT INT 0 0 308

RT DEADTIME SO & RT RT s FLT FLT 0 10 ENGR 210

RT DERIVATIVE RESPONSE ENABLE

SO & RT RT BIT BIT off on ENGR 120

RT DISTANCE SO & RT RT FLT FLT 0 1 ENGR 211

RT DSS DELAY SO & RT RT s FLT FLT 0 0 ENGR 217

RT DSS LEVEL SO & RT RT FLT FLT 0 0 ENGR 216

RT DSS RESPONSE SO & RT RT % FLT FLT 0 1 ENGR 218

RT KD SO & RT RT s FLT FLT 0 64 ENGR 212

RT KP SO & RT RT FLT FLT 0 128 ENGR 214

RT MAX AMPLITUDE SO & RT RT % FLT FLT 0 1 ENGR 215

RT STATUS STATUS STATUS INT LIST 0 0 306

RUNNING STATUS STATUS BIT BIT off on 53

S IN OUT FLT FLT 0 0 102

S CALC UPDATED STATUS STATUS INT INT 0 0 309

S CONTROL START LEVEL

AUTO SEQUENCE S CONTROL % FLT FLT 0 1 ENGR 11

S CONTROL START SPEED

AUTO SEQUENCE S CONTROL rpm FLT FLT 0 0 ENGR 9

S CONTROL STOP SPEED

AUTO SEQUENCE S CONTROL rpm FLT FLT 0 0 ENGR 10

S CONTROLLER COMPANIONS

*VS & CR CR INT PACKET 0 0 ENGR 370

S FAILURE STATUS STATUS BIT BIT off on 54

S TF CONTROL FILTERS s FLT FLT 0 100 ENGR 394

SELECTED I TEST PID FLT FLT 0 0 228

SELECTED P TEST PID FLT FLT 0 0 229

SERIES VS & CR VS BIT BIT paral series ENGR 81

SHUTDOWN MANUAL ENABLE

CONTROL MANUAL BIT BIT off on ENGR 91

SIDE STREAM COMP MODE

SIDE STREAM SS INT LIST 0 4095 ENGR 405

SIDE STREAM COMPANION

SIDE STREAM SS INT PACKET 0 0 ENGR 404

SIGMA IN OUT FLT FLT 0 0 104

SIGMA TF CONTROL FILTERS s FLT FLT 0 100 ENGR 395

SO OPERATOR BIT BIT off on 52

SO B4 SO & RT SO FLT FLT 0 1 ENGR 232

SO B4 RATE SO & RT SO %/s FLT FLT 0 100 ENGR 233

SO BIAS SO & RT SO FLT FLT 0 1 ENGR 224


Data Type

Display Type



Data Access Level

Offset Address



SO DEADTIME SO & RT SO s FLT FLT 0 100 ENGR 225

SO DISTANCE SO & RT SO FLT FLT 0 1 ENGR 226

SO INITIAL SO & RT SO FLT FLT -1 1 ENGR 227

SO TIME BASED ENABLE SO & RT SO BIT BIT off on ENGR 121

SS IN OUT FLT FLT 0 0 103

SS SAMPLES CONTROL FILTERS INT LIST 0 0 ENGR 91

START RATE AUTO SEQUENCE START 1/min FLT FLT 0 1000 ENGR 5

STARTUP TIME AUTO SEQUENCE START s FLT FLT 0 5 ENGR 4

STATE OPERATOR INT STATE 0 0 300

STATUS STATUS STATUS INT PACKET 0 0 408

STOP OPERATOR BIT BIT off on OPER 107

STOP ENABLE AUTO SEQUENCE STOP BIT BIT off on ENGR 160

STOP RATE AUTO SEQUENCE STOP 1/min FLT FLT 0 1000 ENGR 7

STOP STATUS STATUS STATUS BIT BIT off on 162

STOP TIME AUTO SEQUENCE STOP s FLT FLT 0 5 ENGR 6

SUCTION PRESSURE EU ENGINEERING UNITS

ENG UNITS kPa2 INT INT 0 0 ENGR 239

SUCTION PRESSURE2 EU

ENGINEERING UNITS

ENG UNITS kPa2* INT INT 0 0 ENGR 240

SURGE COUNT OPERATOR INT INT 0 0 301

SURGE COUNT RESET OPERATOR BIT BIT off on OPER 102

SURGE COUNT SHUTDOWN RESET

SO & RT SO BIT BIT off on OPER 130

SURGE DZ CONTROL PID FLT FLT 0 1 ENGR 382

SURGE KI CONTROL PID 1/min FLT FLT 0 128 ENGR 383

SURGE KP CONTROL PID FLT FLT 0 128 ENGR 384

SURGE RELAY THRESHOLD

SO & RT SO INT INT 0 0 ENGR 307

SURGES IN OUT INT INT 0 0 OPER 304

T AIR IN OUT K FLT FLT 0 0 482

T AIR GAIN AIR MISER AM FLT FLT 0 10 ENGR 485

T AIR NORMAL AIR MISER AM FLT FLT 0 0 ENGR 484

T CW IN OUT K FLT FLT 0 0 483

T CW GAIN AIR MISER AM FLT FLT 0 10 ENGR 487

T CW NORMAL AIR MISER AM FLT FLT 0 0 ENGR 486

T RATIO IN OUT FLT FLT 0 0 113

TAC IN OUT K FLT FLT 0 0 105

TAC OFFSET SPAN AND OFFSET


TAC SPAN SPAN AND OFFSET


TD IN OUT K FLT FLT 0 0 106

TD DGO SWITCH LEVEL CONFIGURE IO DIGITAL OUT

K* FLT FLT 0 0 ENGR 441

TD OFFSET SPAN AND OFFSET


TD SPAN SPAN AND OFFSET



Data Type

Display Type



Data Access Level

Offset Address

April 20, 1998


TEMPERATURE BASED HP ENABLE


TEMPERATURE CHANNEL

CONFIGURE IO FLOW INT LIST 0 4095 ENGR 97

TEMPERATURE EU ENGINEERING UNITS

ENG UNITS K INT INT 0 0 ENGR 230

TEMPERATURE2 EU ENGINEERING UNITS

ENG UNITS K* INT INT 0 0 ENGR 234

TIGHT SHUT OFF DISTANCE


FLT FLT 0 1 ENGR 53

TIS IN OUT K FLT FLT 0 0 231

TIS OFFSET SPAN AND OFFSET


TIS SPAN SPAN AND OFFSET


TRACK OPERATOR BIT BIT off on OPER 108

TS IN OUT K FLT FLT 0 0 107

TS OFFSET SPAN AND OFFSET


TS SPAN SPAN AND OFFSET


UP OPERATOR INT INT 0 0 OPER 92

USER IN OUT FLT FLT 0 0 108

USER OFFSET SPAN AND OFFSET

OFFSET FLT FLT 0 0 ENGR 432

USER SPAN SPAN AND OFFSET


VALVE CHARACTERIZER



VALVE DEADBAND BIAS CONFIGURE IO CONTROL VALVE


VALVE DEADBAND BIAS THRESHOLD



VALVE MODE CONFIGURE IO CONTROL VALVE


VALVE SHARING COMPANIONS

VS & CR VS INT PACKET 0 0 ENGR 380

VALVE SHARING MODE VS & CR VS BIT BIT sec prim ENGR 150

VARIABLE LIST VAR LIST BIT BIT off on ENGR 200

VS OPERATOR BIT BIT off on 103

VS CV LTOP *VS & CR VS INT LTOP 0 ENGR 590

VS I LTOP *VS & CR VS INT LTOP 0 ENGR 570

VS P LTOP *VS & CR VS INT LTOP 0 ENGR 560

VS RT STATUS STATUS BIT BIT off on 63

VS S LTOP *VS & CR VS INT LTOP 0 ENGR 580

VS STATUS STATUS STATUS INT LIST 0 0 94


Data Type

Display Type



Data Access Level

Offset Address




April 20, 1998

4-15

Chapter 4:

ParameterDescriptions

The remainder of this chapter provides descriptions of the Antisurge Controller database parameters, listed by Parameter Name in alphabetical order.

Alarm

This parameter indicates the presence of a new alarm condition within the controller. It is On when a new alarm is added to the Alarm Buffer. The Alarm Reset parameter is used to clear the Alarm Buffer and reset the Alarm parameter to Off.

Refer to Alarms on page 5-11. Table 6-2 on page 6-3 lists the Antisurge Controller alarm codes.

Alarm Buffer

This parameter is a queue of 20 integers containing a list of the 20 most recent alarms. Whenever a new alarm is added to a full buffer, the oldest alarm in the queue is discarded. The Alarm Reset parameter is used to clear the alarm buffer.

Refer to Alarms on page 5-11. Table 6-2 on page 6-3 lists the Antisurge Controller alarm codes which can appear in the buffer.

Alarm Reset

This parameter is used to clear alarm codes from the Alarm Buffer and reset the Alarm parameter to Off.

Refer to Alarms on page 5-11.

Alpha

This parameter gives the current value of the inlet guide vane angle signal after the Alpha Span and Alpha Offset have been applied to the input.

Alpha Offset

This parameter is used to specify the offset applied to the guide vane angle input from the field transmitter to produce the value of the Alpha parameter.

Refer to Process Variable Scaling on page 3-18.


4-16

Alpha Span

This parameter is used to specify the span applied to the guide vane angle input from the field transmitter to produce the value of the Alpha parameter.


Alternate K

This parameter is used to specify the default surge limit line slope coefficient (K) applied when the alternate K fallback strategy is enabled and active. When Alternate K Enable is On, a primary valve-sharing controller will calculate Ss using Alternate K, instead of K, whenever there is a loss of communication with one or more of its designated valve-sharing companion controllers.

Refer to Valve-Sharing Fallback on page 3-30.

Alternate K Enable

This parameter is used to enable the alternate K fallback strategy. When this parameter is On, a primary valve-sharing controller will calculate Ss using Alternate K, instead of K, whenever there is a loss of communication with one or more of its designated valve-sharing companion controllers.

Refer to Valve-Sharing Fallback on page 3-30.

Analog Inputs

This parameter defines sources for the various analog input parameters (see Controller Inputs and Outputs on page 3-13). Only one source can be defined for each parameter.

Each analog input in the array is mapped to an equivalent database parameter in the controller. The following is a listing of the Analog Inputs array elements, each followed by a parameter reference.

■ dPo1: see dPo1 on page 4-33

■ Ps: see Ps on page 4-72

■ dPo2: see dPo2 on page 4-34

■ Pd: see Pd on page 4-62

■ dPc: see dPc on page 4-30

■ Ts: see Ts on page 4-100

■ Td: see Td on page 4-98

April 20, 1998

4-17

■ Tac: see Tac on page 4-98

■ dTc: see dTc on page 4-37

■ N: see N on page 4-60

■ Alpha: see Alpha on page 4-15

■ kW: see kW on page 4-51

■ Pvi: see Pvi on page 4-75

■ spare1: spare location

■ SO Initial: see SO Initial on page 4-92

■ Pd Limit SP: see Pd Limit SP on page 4-63

■ Ps Limit SP: see Ps Limit SP on page 4-73

■ Remote Low Clamp: see Remote Low Clamping on page 4-82

■ spare2: spare location

■ Control Override: see Control Override SP on page 4-19

■ dPo Side: see dPo Side on page 4-33

■ Position: see Pos on page 4-69

■ Pis: see Pis on page 4-66

■ Tis: see Tis on page 4-100

Analog Outputs

This parameter defines destinations for the various analog output parameters (see Controller Inputs and Outputs on page 3-13). Only one or two destinations can be defined for each parameter.

Each analog output in the array is mapped to an equivalent database parameter in the controller. The following is a listing of the Analog Outputs array elements, each followed by a parameter reference.

■ Out: see Output on page 4-61

■ Ss: see Ss on page 4-92

■ b: see b on page 4-18

■ Dev: see Deviation on page 4-27

■ Rc: see Rc on page 4-80

■ S: see S on page 4-85

Antichoke Enable

This parameter is used to configure the Antisurge Controller to operate as an Antichoke Controller.

Refer to Antichoke Control on page 3-81.


4-18

Antisurge Status

This parameter gives the Status of a Valve Sharing Controller.

Refer to Valve Sharing on page 3-57.

Antisurge Status LTOP

This parameter is an LTOP array used to obtain the value of the Status parameter from a Valve Sharing Controller.


App Name

This parameter is used to configure the OIM name within the Antisurge Controller, and is limited to 16 characters.

App Short Name

This parameter is used to define the short OIM name within the controller, and is limited to five characters.

b

This parameter gives the value of the Safety Margin calculated within the Antisurge Controller. The Safety Margin, which is the distance between the Surge Limit Line and Surge Control Line, is the sum of the Safety On control response (CRSO) and the derivative control response (CRD):

b = CRSO + CRD

Refer to Control Lines on page 3-8 and Safety Margin (b) on page 3-10.

Beta 3

This parameter is used to specify the load-sharing threshold for the Antisurge Controller. When the value of the S variable is greater than Beta 3, the load-sharing response can be applied to the output of the controller.

Refer to Load-Sharing Response on page 3-65.

Beta 5

This parameter is used to specify the scaling coefficient for the load-balancing factor, R, used in load-sharing systems for compressors operating in series.

Refer to Mass Flow Rate on page 3-22.

April 20, 1998

4-19

Config Show Group

This parameter is used to select the parameter groups to be displayed on Configurator. Each of the groups shown in the table below is set to 1 to display the parameters in that group on Configurator. Setting a group to 0 will hide the parameters in that group.

Control Override

This parameter gives the status of the control override function within the Antisurge Controller. When this parameter is set to On by asserting the Control Override digital input, the Output of the controller is tracking an analog input configured as the Control Override SP. When Control Override is Off, this function is disabled.

Refer to Control Override on page 3-77.

Control Override SP

This parameter gives the value of the analog input configured as the set point for the control override function. When Control Override is On, the Output of the Antisurge Controller will track the Control Override SP. This parameter is linked to the analog input using the Analog Inputs LTOP array.


Value Config Show Group

0 CONTROLLERS

1 LOOP DECOUPLE

2 LOAD SHARE

3 AIR MISER

4 RECYCLE BALANCE

5 SIDE STREAM

6 VS & CR

7 LIMIT CONTROL

8 POC

9 ALARM FT

a TEST

b OIM NAMES

c VAR LIST


4-20

Controller Status

This parameter gives the current operating status of the Antisurge Controller. The possible values of this parameter are listed below.

Refer to Main Control Screen on page 5-1.

Controller Type

This parameter indicates whether the controller is operating as an Antisurge Controller, an S Controller, or an Antichoke Controller, as listed below.

Value Controller Status

0 SHUTDOWN

1 PURGE

2 RUN

3 TRACKING

4 MANUAL RUN

5 MANUAL SD

6 REMOTE RUN

7 STOPPING

8 STARTING

9 RUN NEXT SD

10 IDLE

Value Controller Type

0 ANTISURGE

1 S CONTROL

2 ANTICHOKE

April 20, 1998

4-21

Current dCV

This parameter indicates which delta control variable (dCV) is currently signal-selected by the Antisurge Controller. The possible values of this parameter are listed below.

Refer to Antisurge Controller Functions on page 3-34.

CV

This parameter gives the current value of the control variable (CV) calculated within the Antisurge Controller. This value, used only for loop decoupling, is calculated by incrementing its value from the previous cycle by the signal-selected dCV and the Recycle Trip opening response (dCVRT, opening) for the current cycle:

CVn = CVn-1 + dCV + dCVRT, opening

When the absolute value of CV exceeds 3.0, it will roll back to zero.


CV Total

This parameter gives the current value of the overall control variable calculated for the main control loop after the signal-selected dCV, loop-decoupling, and load-sharing responses have been applied:


The CV Total is the intended recycle flow of the Antisurge Controller, expressed in percent output.


Value Description dCV

0 PRIMARY dCVAS

1 VLV SHARE dCVVS

2 RECYC BAL dCVRB

3 POC dCVPOC

4 PS LIMIT dCVLim

5 PD LIMIT dCVLim

6 RC LIMIT dCVLim

7 COLD RECYCLE dCVS


4-22

dCV

This parameter gives the current value of the signal-selected dCV for the main control loop, expressed in percent. The highest of the dCVPI, dCVLim, dCVRB, dCVPOC, and dCVVS is signal-selected by the controller. The Current dCV parameter indicates which dCV is currently signal-selected.


Decouple CV LTOP

This parameter is an LTOP array used to obtain the value of the CV parameter from each of the companion Loop Decoupling Performance and Antisurge Controllers.

Refer to Loop Decoupling on page 3-63.

Default Adjacent Flow Enable

This parameter is used to enable the adjacent flow fallback strategy. When this parameter is On, the Antisurge Controller will use the Default Adjacent Flow Rate in place of dPo Comp if a valid sidestream flow signal from a designated companion controller is lost.

Refer to Adjacent Flow Fallback on page 3-27.

Default Adjacent Flow Rate

This parameter is used to specify the default upstream or downstream flow signal used when the adjacent flow fallback strategy is enabled and active. When Default Adjacent Flow Enable is On, the Antisurge Controller will use the Default Adjacent Flow Rate in place of a failed dPo Comp from a designated companion controller.

Refer to Adjacent Flow Fallback on page 3-27.

Default Alpha

This parameter is used to specify the default guide vane angle used when the vane angle fallback strategy is enabled and active. When Default Alpha Enable is On, the Antisurge Controller will use the Default Alpha value in place of Alpha if the guide vane position input fails.

Refer to Guide Vane Angle Failure on page 3-33.

April 20, 1998

4-23

Default Alpha Enable

This parameter is used to enable the guide vane angle fallback strategy. When this parameter is On, the Antisurge Controller will use the Default Alpha value in place of Alpha if the guide vane position input fails. If this parameter is Off when the Alpha input fails, the controller will continue to calculate the S variable using the invalid vane angle.

Refer to Guide Vane Angle Failure on page 3-33.

Default Output

This parameter is used to specify the default output used when the run freeze fallback strategy is active. This fallback forces the controller into a suspended Run mode and initializes the Output parameter to the higher of the Default Output parameter or a filtered output value. Setting the Default Output parameter to zero will cause the controller to select the filtered output.

Refer to Run Freeze Fallback on page 3-30.

Default Ps

This parameter is used to specify the default suction pressure used when the suction pressure fallback strategy is enabled and active. When Default Ps Enable is On, the Antisurge Controller will use the Default Ps in place of Ps for all calculations if the suction pressure input fails.

Refer to Suction Pressure Failure on page 3-32.

Default Ps Enable

This parameter is used to enable the suction pressure fallback strategy. When this parameter is On, the controller will use the Default Ps in place of Ps for all calculations if the suction pressure input fails.

Refer to Suction Pressure Failure on page 3-32.

Default Rc

This parameter is used to specify the default compression ratio used when the compression ratio fallback strategy is enabled and active. When Default Rc Enable is On, the controller will use the Default Rc in place of the calculated Rc if any pressure input needed to calculate the compression ratio fails.

Refer to Compression Ratio Fallback on page 3-28.


4-24

Default Rc Enable

This parameter is used to enable the compression ratio fallback strategy. When this parameter is On, the controller will use the Default Rc in place of the calculated Rc if any pressure input needed to calculate the compression ratio fails.

Refer to Compression Ratio Fallback on page 3-28.

Default Sigma

This parameter is used to specify the default sigma used when the sigma fallback strategy is enabled and active. When Default Sigma Enable is On, the controller will use the Default Sigma in place of Sigma if any temperature or pressure inputs needed to calculate the polytropic head exponent fail.

Refer to Sigma Fallback on page 3-30.

Default Sigma Enable

This parameter is used to enable the sigma fallback strategy. When this parameter is On, the controller will use the Default Sigma in place of Sigma if any temperature or pressure inputs needed to calculate the polytropic head exponent fail.

Refer to Sigma Fallback on page 3-30.

Default Speed

This parameter is used to specify the default speed applied when the speed fallback strategy is enabled and active. When Default Speed Enable is On, the controller will use the Default Speed in place of N for any surge line calculations if the speed input fails.

Refer to Speed Failure on page 3-32.

Default Speed Enable

This parameter is used to enable the speed fallback strategy. When this parameter is On, the controller will use the Default Speed in place of N for any calculations if the speed input fails. If this parameter is Off when the speed input fails, the controller will continue to calculate S using the invalid speed.

Refer to Speed Failure on page 3-32.

April 20, 1998

4-25

Denominator

This parameter gives the current value of the denominator used in the calculation of the proximity-to-surge variable, Ss.

Refer to Numerator and Denominator Modes on page 3-3.

Denominator Mode

This parameter is used to specify the denominator variable (X) used in the calculation of the proximity-to-surge variable Ss:

The denominator modes are listed in the following table.


Derivative Response DB

This parameter is used to specify the dead band applied to the derivative response (CRD) calculated within the Antisurge Controller.

Refer to Derivative Response on page 3-41.

Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=

Name Denominator Mode (X) Description

S CONTROL S control (see page 3-69)DPO X = dPo Calc calculated flow measurement

DPO DIV PS X = dPo Calc / ps reduced flow squared

DPO DIV PD X = dPo Calc / pd reduced flow in discharge squared

NO FLOW X = Ne2 = N

2 / Ts

when a flow measurement is not available, proximity to surge can be computed by replacing the flow parameter with the equivalent speed (Ne) squared.Note : This denominator mode is valid only when molecular weight is nearly constant.


4-26

Derivative Response Enable

This parameter is used to enable the derivative response (CRD) of the Antisurge Controller. When this parameter is set to On, the derivative response varies the Safety Margin (b) as a function of the rate at which the operating point is approaching the Surge Limit Line (SLL).


Derivative Response Max

This parameter is used to specify the maximum allowable value of the derivative response (CRD) calculated within the Antisurge Controller. The calculated derivative response (CRD) is compared to the Derivative Response Max, and the smaller of the two used as the derivative control response.


Derivative Response Rate

This parameter is used to specify the decay rate of the derivative response (CRD) calculated within the Antisurge Controller. When the operating point is moving away from the surge limit, CRD is ramped back to zero at the rate specified by the Derivative Response Rate parameter.

This parameter is also used to specify the rate at which the additional margin of safety (b4) is ramped to the value of SO b4 when b4 is decreasing.

Refer to Derivative Response on page 3-41 and Safety On Response on page 3-47.

Derivative Response Tc

This parameter is used to specify the gain applied to the derivative response (CRD) calculated within the Antisurge Controller.


Dev Threshold

This parameter is used to specify the run level for the controller Deviation. The Antisurge Controller will transfer from the Starting state to the Run state when the Deviation falls below the Dev Threshold.

Refer to Starting State on page 3-88.

April 20, 1998

4-27

Deviation

This parameter gives the relative distance between the current position of the compressor operating point and the Surge Control Line (SCL). It is used primarily for display purposes and is calculated by complementing S:

Deviation = 1 – S = 1 – [Ss + b · f4(Z4)]

Refer to Operating Point on page 3-12.

Digital Inputs (2)

This parameter defines sources for various digital inputs (see Controller Inputs and Outputs on page 3-13). As many as two sources can be defined for each input, which are combined with a logical OR. Therefore, an input will be evaluated as true if either of its assigned sources is true.

Many of the digital inputs in the array are mapped to an equivalent database parameter in the controller. The following is a listing of the Digital Inputs (2) array elements, each followed by an input type in parenthesis, and either a parameter reference or a description.

■ Purge: (Level) see Purge on page 4-75

■ spare: spare location

■ SO Reset: (Level) This input clears the Surge Count parameter, resets the Safety On response (CRSO), resets the SO parameter to Off, resets the accumulated Safety On bias (b2) to zero, and initializes the PID to prevent a bump in the controller output.

■ Reset: (Level) see Alarm Reset on page 4-15

■ Auto: (Edge) see Manual Auto on page 4-54

■ Manual: (Edge) see Manual Auto on page 4-54

■ Manual Auto: (Cumulative) see Manual Auto on page 4-54

■ Up: (Level) see Up on page 4-101

■ Down: (Level) see Down on page 4-30

■ MOR: (Level) see Manual Override on page 4-55

■ Control Override: (Level) This input tells the Antisurge Controller when to track the configured analog input. When this input is On, the output of the controller will track the Control Override SP.


4-28

■ LS Run Status: (Level) This input gives the run status of the Load Sharing Controllers. When this input is Off and the Check Vlv Status input is Open, the additional margin of safety (SO b4) is added to the Safety On control response.

■ Check Vlv Status: (Level) This input gives the open/closed status of the check valve, in applications which use a check valve. When this input is Open and the LS Run Status input is Off, the additional margin of safety (SO b4) is added to the Safety On control response.

■ POC Valid: (Level) This input gives the value of the POC Valid parameter from the Master. When this input is On, the change in the POC control variable from the Master will be compared with the value of the dCV within the Antisurge Controller, and the highest value selected.

■ Disable RB: (Level) This input is used to disable the recycle-balancing function within the Antisurge Controller. Recycle balancing will be disabled and the RB Valid set to False when the Disable RB digital input is set.

■ N Fail: (Level) This input indicates a failure of the speed input.

Digital Inputs (8)

This parameter defines sources for the various digital inputs (see Controller Inputs and Outputs on page 3-13). As many as eight sources can be defined for each input, which are combined with a logical OR. Therefore, an input will be evaluated as true if any of its assigned sources is true.

The following is a listing of the Digital Inputs (2) array elements, each followed by an input type in parenthesis and a parameter reference.

■ Stop: (Level) see Stop on page 4-94

■ ESD: (Level) see ESD on page 4-38

Digital Outputs

This parameter defines destinations for the various digital outputs (see Controller Inputs and Outputs on page 3-13). As many as two destinations can be defined for each input.

Many of the digital outputs in the array are assigned from an equivalent database parameter in the controller. The following is a listing of the Digital Outputs array elements, each followed by an output type in parenthesis and either a parameter reference or a description.

April 20, 1998

4-29

■ Auto: (Self-Clearing) This output is set to 1 to indicate that the Antisurge Controller is operating in the Automatic control mode.

■ Limit: (Self-Clearing) see Limit on page 4-53

■ Alarm: (Self-Clearing) see Alarm on page 4-15

■ Unload Complete: (Self-Clearing) This output is set to 1 when the controller is shut down and the Output is at the Output High Limit. It is cleared when an emergency shutdown (ESD) is triggered in the Series 4 Speed Controller.

■ Out Fail: (Self-Clearing) This output is set to 1 to indicate a failure of the Antisurge Controller output (Output).

■ RT: (Self-Clearing) see RT on page 4-82

■ SO: (Self-Clearing) see SO on page 4-90

■ Surge: (Self-Clearing) see Exc Surge on page 4-39

■ Out High Clamp: (Self-Clearing) see High Clamp on page 4-49

■ Out Low Clamp: (Self-Clearing) see Low Clamp on page 4-54

■ Pos Deviation: (Self-Clearing) This output is set to 1 to indicate that the difference between the Position analog input (Pos) and the output of the controller (Output) has exceeded the value of the Pos Delta Max parameter for the amount of time specified by the Pos Delta Delay parameter. An alarm is also generated.

■ Control Override: (Self-Clearing) see Control Override on page 4-19

■ Xmit Fail: (Self-Clearing) This output is set to 1 to indicate a transmitter failure to the Antisurge Controller. An alarm is also generated.

■ Pd Level Switch: (Self-Clearing) This output is set to 1 to indicate that the discharge pressure exceeds the value of the Pd DGO Switch Level parameter. It is cleared when the discharge pressure drops below the switch level by 0.5% of the Pd Span.

■ Ps Level Switch: (Self-Clearing) This output is set to 1 to indicate that the suction pressure is below the value of the Ps DGO Switch Level parameter. It is cleared when the suction pressure rises above the switch level by 0.5% of the Ps Span.


4-30

■ Td Level Switch: (Self-Clearing) This output is set to 1 to indicate that the discharge temperature exceeds the value of the Td DGO Switch Level parameter. It is cleared when the discharge temperature drops below the switch level by 0.5% of the Td Span.

■ Hard Manual: (Self-Clearing) This output is set to 1 when the manual override function is active.

Display Output

This parameter contains the current value of the intended recycle valve position (Output) from the Antisurge Controller, before the Output Reverse function is applied. Therefore, zero always corresponds to fully closed and 100% to fully open.

Refer to Control Element Compensation on page 3-72.

Down

This parameter is used to manually position the antisurge valve. Each time the Down parameter is asserted, the output from the Antisurge Controller is lowered at the rate specified by the Manual Rate Close parameter. The Down parameter is automatically reset to Off after each decrement in the output. As a result, the Down parameter must be asserted each time additional manipulation of the Antisurge Controller output is desired.

Refer to Manual State on page 3-89.

dPc

This parameter gives the current value of the delta pressure signal across the compressor after dPc Span and dPc Offset have been applied to the input.

dPc Offset

This parameter is used to specify the offset applied to the delta pressure input from the field transmitter to produce the value of the dPc parameter.


April 20, 1998

4-31

dPc Span

This parameter is used to specify the span applied to the delta pressure input from the field transmitter to produce the value of the dPc parameter.


dPo Calc

This parameter gives the value of the compensated flow used in the calculation of the Surge Control Line (SCL).

Refer to Calculated Variables on page 3-20.

dPo Comp

This parameter gives the value of the flow measurement reported to sidestream controllers, from the Antisurge Controller with the upstream or downstream flow measurement, for flow calculation of sidestream stages.

Refer to Multisection Compressor Flow Rates on page 3-24.

dPo Dev

This parameter indicates that the difference between the redundant dPo1 and dPo2 inputs exceeds the threshold specified by dPo Differential Threshold parameter.

Refer to Redundant Signal Selection on page 3-17.

dPo Differential Threshold

This parameter is used to specify the maximum allowable difference between the redundant dPo1 and dPo2 inputs. When the differential is exceeded, the dPo Dev parameter will be On.



4-32

dPo Rate

This parameter is used to specify the threshold for the flow derivative signal when a flow-based Emergency Antisurge mode (EAS Mode) is selected.

This value can be entered as either a positive or negative floating-point number. A positive value specifies that the flow derivative signal must exceed this value before the Surge Count parameter is incremented. A negative value specifies that the dPo derivative signal must be more negative than this value to increment the Surge Count parameter.

As an aid to setting this rate-of-change threshold, the controller records the most positive flow derivative in Max +dPo and the most negative flow derivative in Max -dPo. An appropriate dPo Rate can be determined by setting these parameters to zero before surge testing the compressor.

Refer to EAS Surge Detection on page 3-50.

dPo Samples

This parameter is used to specify the number of dPo samples used by the Emergency Antisurge (EAS) algorithm to determine the dPo derivative. It can be set to the values listed in the following table.

A value of four or eight samples is recommended for most applications.


dPo Select

This parameter indicates the source of the dPo signal, as shown in the following table.


Value dPo Samples

4 SAMPLES 4

8 SAMPLES 8

c SAMPLES 12

10 SAMPLES 16

Value dPo Signal

0 DPO1

1 DPO2

April 20, 1998

4-33

dPo Side

This parameter contains the value of the sidestream delta pressure signal after dPo Side Span and dPo Side Offset have been applied to the input.

dPo Side Offset

This parameter is used to specify the offset applied to the sidestream delta pressure input from the field transmitter to produce the value of the dPo Side parameter.


dPo Side Span

This parameter is used to specify the span applied to the sidestream delta pressure input from the field transmitter to produce the value of the dPo Side parameter.


dPo Used

This parameter gives the value of the selected flow measurement. If the controller has redundant dPo1 and dPo2 inputs, dPo Used will be set to the lower input. The dPo Select parameter indicates which signal is being used.


dPo1

This parameter contains the current value of the delta pressure 1 signal after dPo1 Span and dPo1 Offset have been applied to the input.

dPo1 Offset

This parameter is used to specify the offset applied to the delta pressure 1 input from the field transmitter to produce the value of the dPo1 parameter.


dPo1 Span

This parameter is used to specify the span applied to the delta pressure 1 input from the field transmitter to produce the value of the dPo1 parameter.



4-34

dPo2

This parameter contains the current value of the delta pressure 2 signal after dPo2 Span and dPo2 Offset have been applied to the input.

dPo2 Offset

This parameter is used to specify the offset applied to the delta pressure 2 input from the field transmitter to produce the value of the dPo2 parameter.


dPo2 Span

This parameter is used to specify the span applied to the delta pressure 2 input from the field transmitter to produce the value of the dPo2 parameter.


April 20, 1998

4-35

dPos Mode

This parameter is used to specify the method the controller uses to compensate the flow measurement (dPo Used) for the calculation of the Surge Control Line (SCL). The method used to calculate dPo Calc is selected from the dPos Modes listed in the following table.


Name dPo Calc = Description

S CONTROL S control (see page 3-69)SUCTION dPo Used When dPo Used is a suction flow

measurement, it can be used without any compensation being applied.

DISCHARGE dPo Used · (Rc / T Ratio) When dPo Used is a measurement of discharge flow, dPo Calc can be calculated from dPo Used, the compression ratio (Rc), and the temperature ratio (T Ratio).

AFTERCOOL dPo Used · Rc · (Ts / Tac) When dPo Used is the flow downstream of an aftercooler, dPo Calc can be calculated from dPo Used, Rc, and the suction and aftercooler temperatures (Ts and Tac).

RC CHAR dPo Used · f5(Rc) When dPo Used represents the flow downstream of an aftercooler, and the temperatures are not measured, dPo Calc can be calculated by multiplying dPo Used by a function of the compression ratio (Rc), where f5 is defined by f5 Characterizer.

RC COMPdPo Used · Rc

1-σWhen dPo Used represents the flow downstream of an aftercooler, and the temperatures are not measured, dPo Calc can be calculated from dPo Used and the Default Sigma (σ).

VLVE INLET dPo Used · (Pvi / Ps) When the flow is measured upstream of an inlet valve, dPo Calc can be calculated from dPo Used and the pressure on each side of the restriction.

INTERSTAGE dPo Used · (Pis / Pd) · (Td / Tis)

When the flow is measured between compressor stages, dPo Calc can be calculated from dPo Used and the interstage pressure and temperature.


4-36

dPressure EU and dPressure2 EU

This parameter is used to convert pressure values from kilopascals to another unit of measure for display on an OIM or OIS. The conversions available in the controller are given in the following table.

dPressure Rate EU

This parameter is used to convert delta pressure rate values from kilopascals per second to another unit of measure for display on an OIM or OIS. The conversions available in the controller are given in the following table.

dPressure2 EU

See description for dPressure EU and dPressure2 EU.

Value Units Description

0 kPa1 kilopascals (no conversion)

1 bar bars

2 psia pounds/square inch absolute

3 psig pounds/square inch gauge

4 atmS atmospheres

5 N/m2 Newtons/square meter

6 inH2O inches of water

7 kg/cm2 kilograms/square centimeter

8 atmT technical atmospheres

9 mmH2O millimeters of water

10 barg bars gauge

11 kg/cm2g kilograms/square centimeter gauge

12 mbar millibars


0 kPa1/s kilopascals/second (no conversion)

1 bar/s bars/second

2 psia/s pounds/square inch absolute/second

3 psig/s pounds/square inch gauge/second

4 atmS/s atmospheres/second

5 N/m2/s Newtons/square meter/second

6 inH2O/s inches of water/second

7 kg/cms kilograms/square centimeter/second

8 atmT/s technical atmospheres/second

9 mmH2O/s millimeters of water/second

10 barg/s bars gauge/second

11 kg/cm2sg kilograms/square centimeter gauge/second

12 mbar/s millibars/second

April 20, 1998

4-37

dSs

This parameter gives the current value of the computed derivative of the proximity-to-surge variable, Ss. This value (dSs/dt) is used in the Derivative Response (see page 3-41), the Recycle Trip Derivative Response (see page 3-44), and the Recycle Trip dSs Response (see page 3-45).

dSs Max

This parameter shows the maximum value of computed derivative of the proximity-to-surge variable (dSs/dt) that has occurred.


dTc

This parameter gives the current value of the delta temperature across the compressor after dTc Span and dTc Offset have been applied to the input.

dTc Offset

This parameter is used to specify the offset applied to the delta temperature input from the field transmitter to produce the value of the dTc parameter.


dTc Span

This parameter is used to specify the span applied to the delta temperature input from the field transmitter to produce the value of the dTc parameter.


EAS

This parameter gives the status of the Emergency Antisurge (EAS) function within the Antisurge Controller. It is set to On when a pressure or flow derivative exceeds its specified threshold (Pd Rate or dPo Rate). EAS will be cleared when the pressure or flow derivative falls back below the threshold.



4-38

EAS Mode

This parameter is used to select the algorithm for the Emergency Antisurge (EAS) detection function. The EAS Modes are listed in the following table.


ESD

This parameter is used to request an emergency shutdown of the compressor. When ESD is asserted the recycle valve opens immediately and the controller will go to the Shutdown state.

Refer to Shutdown State on page 3-86.

ESD Status

This parameter is set to On when the Antisurge Controller has been stopped using the ESD parameter or ESD digital input. It is used to allow other controllers to get the condition of the Antisurge Controller directly from this value.


EAS Mode Description

DISABLED EAS detection disabled.DPO AND PD EAS detected when both the flow derivative exceeds

dPo Rate and the discharge pressure derivative exceeds Pd Rate.

DPO OR PD EAS detected when either the flow derivative exceeds dPo Rate or the discharge pressure derivative exceeds Pd Rate.

DPO EAS detected when the flow derivative exceeds dPo Rate.

PD EAS detected when the discharge pressure derivative exceeds Pd Rate.

April 20, 1998

4-39

Exc Surge

This parameter is set to On when the Surge Count is greater than or equal to the number of surges specified with the Surge Relay Threshold parameter.

Exc Surge is reset to Off when Surge Count Reset is set to On; when the SO Reset digital input is asserted; or upon entering the Shutdown state when Surge Count Shutdown Reset is On.

The Surge digital output is assigned from the value of Exc Surge.

Refer to Safety On Response on page 3-47.

f1 Characterizer

This parameter is used to configure the f1 characterizing function used in the calculation of the proximity-to-surge variable, Ss. The f1 characterizer is used in the following equation to characterize the Surge Limit Line (SLL):

This parameter is entered as ten data pairs consisting of the argument Z1 and the function f1(Z1). The controller uses linear interpolation to calculate intermediate values of the f1 characterizer. Normal values for the f1 characterizer should be positive floating-point numbers.

The argument, Z1, is specified using the f1 Characterizer Mode parameter.


Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=


4-40

f1 Characterizer Mode

This parameter is used to configure the argument for the f1 characterizing function in the calculation of the proximity-to-surge variable Ss:

This parameter can be set to any of the variables listed in the following table.


f2 Characterizer

This parameter is used to configure the f2 characterizing function used in the calculation of the proximity-to-surge variable, Ss. The f2 characterizer is used in the following equation to characterize the Surge Limit Line (SLL):

This parameter is entered as ten data pairs consisting of the argument Z2 and the function f2(Z2). The controller uses linear interpolation to calculate intermediate values of the f2 characterizer. Normal values for the f2 characterizer should be positive floating-point numbers.

The argument, Z2, is specified using the f2 Characterizer Mode parameter.


Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=








Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=

April 20, 1998

4-41


This parameter is used to configure the argument for the f2 characterizing function in the calculation of the proximity-to-surge variable Ss:

This parameter can be set to any of the variables listed in the following table.


f3 Characterizer

This parameter is used to configure the f3 characterizing function used in the calculation of the proximity-to-surge variable, Ss. The f3 characterizer is used when the Numerator Mode parameter is set to FUNC HP or FUNC HP TS.

This parameter is entered as ten data pairs consisting of the argument and the function f3. The controller uses linear interpolation to calculate intermediate values of the f3 characterizer. Normal values for the f3 characterizer should be positive floating-point numbers. The argument is selected using the f3 Characterizer Mode parameter.


Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=









4-42


This parameter is used to specify the argument for the f3 characterizer. It can be set to any of the variables listed in the following table.


f4 Characterizer

This parameter is used to configure the control line characterizer used in the calculation of the Surge Control, Recycle Trip, Safety On, and Tight Shut-Off Lines.

The f4 Characterizer parameter is entered as ten data pairs consisting of the argument and the f4 function. The controller uses linear interpolation to calculate intermediate values of the f4 characterizer. Normal values for the f4 characterizer should be positive floating-point numbers.

Refer to Control Lines on page 3-8.








April 20, 1998

4-43


This parameter is used to configure the argument of the f4 Characterizer used in the calculation of the Surge Control line, Recycle Trip Line, Safety On Line, and Tight Shut-Off Line.

The argument (Z4) for this function is specified by setting the f4 Characterizer Mode parameter to one of the options listed in the following table.

Refer to Control Line Characterizer on page 3-9.

f5 Characterizer

This parameter is used to compensate for the location of the flow measuring device. The f5(Rc) characterizer is utilized when dPos Mode is set to RC CHAR or Side Stream Comp Mode is set to FUNC RC.

This characterizer is entered as ten data pairs consisting of the argument and the f5 function. The controller uses linear interpolation to calculate intermediate values of the f5 characterizer. Normal values for the f5 characterizer should be positive floating-point numbers.

Refer to Numerator and Denominator Modes on page 3-3 and Reported Flow on page 3-22.

Argument f4 Characterizer Mode

DISABLED 1 (Linear) — f4=1

DPO ∆po — compensated suction flow measurement (dPo Calc)

ALPHA α — guide vane angle process variable

SPEED N — rotational speed process variable


4-44

f6 Characterizer

This parameter is used to configure the characterizing function used in the calculation of the proximity-to-surge variable Ss. The f6(x) characterizer is used when the Numerator Mode parameter is set to FUNC RC, FUNC HP, or FUNC HP TS.

This parameter is entered as ten data pairs consisting of the argument and the f6 function. The controller uses linear interpolation to calculate intermediate values of the f6 characterizer. Normal values for the f6 characterizer should be positive floating-point numbers.


Fallback

This parameter indicates when the Antisurge Controller has entered a fallback strategy. It is On when a fallback strategy is active and is Off at all other times.

Refer to Fallback Strategies on page 3-27.

Filtered POC Valid

This parameter indicates that the filtered POC response (dCVPd) is greater than zero.

Refer to Filtered POC Response on page 3-62.

Flow

This parameter gives the current value of the mass flow rate, calculated from specified flow, temperature, and pressure measurements, all of which must correspond to the same physical location (generally an orifice plate installed in the suction or discharge line):


Flow CF

∆po po⋅To

--------------------=

April 20, 1998

4-45

Flow Channel

This parameter is used to specify the analog input channel for the delta pressure (∆po) signal used in the mass flow calculation:

Flow Channel is set to the input below which corresponds to the temperature and pressure where the flow is measured.


Flow Coefficient

This parameter is used to specify the mass flow scaling coefficient (CF) used in the following mass flow calculation:

Note: When specifying the value of CF (Flow Coefficient), the user must calculate a value consistent with the pressure and temperature units used in the equation.


Value Flow Channel

– DISABLED

0 DPO

1 DPO SIDE

Flow CF

∆po po⋅To

--------------------=

Flow CF

∆po po⋅To

--------------------=


4-46

Flow EU

This parameter is used to convert mass flow values from kilograms per second to another unit of measure for display on an OIM or OIS. The conversions available in the controller are given in the following table.

Flow Offset

This parameter is used to specify the offset for calculating the normalized mass flow rate reported by the Modbus register:


Flow Sidestream Coefficient 1

This parameter is used to specify the value of the flow coefficient (C1) for the mass balance equation:

This equation is used to calculate a combined flow measurement (dPo Used) from the main and sidestream flow measurements (dPo Comp and dPo Side).



0 kg/s kilograms/second (no conversion)

1 lb/h pounds (mass)/hour

2 ton/h tons/hour

3 TON/h metric tons/hour

4 kph kilopounds/hour

5 SCFM standard cubic feet/minute

6 SCFH standard cubic feet/hour

7 MSCFH 1000 standard cubic feet/minute

8 NCMM normal cubic meters/minute

9 NCMH normal cubic meters/hour

WnModbus 4095


-------------------------------------------------- ⋅=

po∆ C1 po 1,∆⋅( ) C2 po 2,∆⋅( ) C3 po 1,∆ po 2,∆⋅+ +=

April 20, 1998

4-47









Flow Span

This parameter is used to specify the span for calculating the normalized mass flow rate reported by the Modbus register:


Flow->Pressure Time Lag

This parameter is used in EAS surge detection when the EAS Mode parameter is configured to DPO AND PD. When this mode is selected, both the flow derivative and the discharge pressure derivative must exceed their respective thresholds (dPo Rate and Pd Rate) for an EAS surge detection to occur.

An EAS will be detected if the flow derivative exceeds dPo Rate within the time configured by Flow->Pressure Time Lag after the pressure derivative has exceeded Pd Rate.


po∆ C1 po 1,∆⋅( ) C2 po 2,∆⋅( ) C3 po 1,∆ po 2,∆⋅+ +=

po∆ C1 po 1,∆⋅( ) C2 po 2,∆⋅( ) C3 po 1,∆ po 2,∆⋅+ +=

WnModbus 4095


-------------------------------------------------- ⋅=


4-48

FT Alarm Level

This parameter is an array used to assign a criticality level to each of the Antisurge Controller error conditions listed in the table below.

Array Index

Error Condition Description

0 DPO FAIL delta pressure input failure

1 DPO1 FAIL delta 1 pressure input failure

2 DPO2 FAIL delta 2 pressure input failure

3 PS FAIL suction pressure input failure

4 PD FAIL discharge pressure input failure

5 DPC FAIL delta pressure across compressor input failure

6 DPO SIDE FAIL delta pressure sidestream input failure

7 PVI FAIL valve inlet pressure input failure

8 PD LIMIT SP FAIL discharge pressure limit set point failure

9 PS LIMIT SP FAIL suction pressure limit set point failure

A TS FAIL suction temperature input failure

B TD FAIL discharge temperature input failure

C DTC FAIL delta temperature across compressor input failure

D TAC FAIL aftercooler temp input failure

E N FAIL speed input failure

F ALPHA FAIL guide vane angle input failure

10 KW FAIL power input failure

11 VALVE OUT FAIL valve output failure

12 REMOTE LOW CLAMP FAIL remote low clamp failure

13 CONTROL OVERRIDE FAIL control override failure

14 SO INITIAL FAIL safety on initial failure

15 DPO CHANNEL FAIL failure of delta pressure channel

16 P CHANNEL FAIL failure of pressure channel

17 T CHANNEL FAIL failure of temperature channel

18 PIS FAIL interstage pressure input failure

19 TIS FAIL interstage temperature input failure

1A PS1 FAIL suction pressure 1 input failure

1B PS2 FAIL suction pressure 2 input failure

1C PD1 FAIL discharge pressure 1 input failure

1D PD2 FAIL discharge pressure 2 input failure

1E TS1 FAIL suction temperature 1 input failure

1F TS2 FAIL suction temperature 2 input failure

20 TD1 FAIL discharge temperature 1 input failure

21 TD2 FAIL discharge temperature 2 input failure

22 DPO SIDE1 FAIL side stream flow 1 input failure

23 DPO SIDE2 FAIL side stream flow 2 input failure

April 20, 1998

4-49

Each of the error conditions in the above FT Alarm Level array is assigned one of the following Series 4 criticality levels:

For example, if a suction pressure failure was deemed to be a fatal error, a 5 would be entered into array index 3 of the FT Alarm Level parameter.

FT Alarm Reset

This parameter is used to monitor the status of fault tolerant AFM switchover attempts. When this parameter is Off, either no switchover attempts have been made or the switchovers have been successful.

If this parameter is On, an unsuccessful switchover attempt has been made. It must be manually reset to Off before any other switchover will be attempted.

Gear Ratio

This parameter is used to scale the speed input signal to be consistent with the actual compressor speed:

N = Npacket · Gear Ratio

It is applied to the speed input received by either packet communication or by analog input.


High Clamp

This parameter indicates when the intended valve position (Output) has reached the level specified by the Output High Limit parameter. High Clamp is Yes when the Output is at the limit and is No at all other times.

Refer to Output Clamps on page 3-72.

Criticality Level Description

0 Not Critical (ignore the failure)

1 Warning (alarm the failure)

2 Switchable level #1 (lowest priority switchover)

3 Switchable level #2 (medium priority switchover)

4 Switchable level #3 (highest priority switchover)

5 Fatal (shutdown)


4-50

History Buffer

This parameter is a queue of 20 integers containing the 20 most recent status codes that have occurred in the controller. Whenever a new status code is added to the buffer, it goes into the first location and all other codes are moved back one place. The oldest code, which was in the last buffer location, is then discarded. The History Reset parameter is used to clear the history buffer.

Only one occurrence of any given alarm code is entered into the history buffer regardless of the number of times the alarm occurred.

Refer to History on page 5-12. Table 6-1 and Table 6-2 list the Antisurge Controller status codes which can appear in the buffer.

History Reset

This parameter is used to reset and clear the History Buffer. It is set to On to clear the buffer.

Refer to History on page 5-12.

Hp

This parameter contains the current value of reduced polytropic head calculated by the Antisurge Controller:

Refer to Reduced Polytropic Head on page 3-21.

I Offset

This parameter is used to specify the offset of the integral term for calculating the cold recycle dCV. It is added to the highest integral term from the S Controller companions to make sure that the cold recycle valve opens first.

Refer to Cold Recycle (S) Control on page 3-69.

hp

Rcσ 1–

σ----------------=

April 20, 1998

4-51

Idle Speed SP

This parameter is used when the compressor is not running (Running = No).

When the speed (N) ia greater than the Idle Speed SP, a purge of the compressor is prohibited and surge protection will still be active.

Refer to Idle State on page 3-87.

K

This parameter is used to specify the Surge Limit Line (SLL) slope coefficient used in the calculation of the proximity-to-surge variable Ss:

Refer to Proximity to Surge on page 3-1.

K Prime

This parameter gives the value of the quantity [K · f1(Z1) · f2(Z2)] in the calculation of the proximity-to-surge variable, Ss:


Ki Adjust

This parameter is used to specify the generic integral gain (Ki) reduction value which establishes the decay rate for the Recycle Trip (see page 3-42), Limiting Control (see page 3-52), Valve Sharing (see page 3-57), and POC (see page 3-60) control responses. The integral portion of these PI responses is reduced by this value to prevent the response from immediately being triggered again.

kW

This parameter contains the current value of the motor power signal after kW Span and kW Offset have been applied to the input.

Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=

Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=


4-52

kW Offset

This parameter is used to specify the offset applied to the motor power input from the field transmitter to produce the value of the kW parameter.


kW Span

This parameter is used to specify the span applied to the motor power input from the field transmitter to produce the value of the kW parameter.


LD Companions

This parameter is an array of 10 module addresses used to designate the companion loop decoupling controllers for the Antisurge Controller. The list of corresponding loop-decoupling coefficients for each controller is specified using the LD Companions Coefficient parameter.

Each element of the array is set equal to the module address of a loop decoupling companion controller. Unneeded elements must be set to zero. Setting all of the elements in the array to zero disables this feature.

The module address for a companion controller uses the following format:

00 XX YY ZZ

where:

■ 00 is a fixed value of 00 hexadecimal.

■ XX is the companion controller group ID number expressed in hexadecimal.

■ YY is the companion controller module number expressed in hexadecimal.

■ ZZ is the companion controller ASP number expressed in hexadecimal.

For example, if a LD Companions element is set to 00010203, the companion controller will be the third ASP of the second module in group 1.


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4-53

LD Companions Coefficient

This parameter is an array of 10 floating-point values used to specify the loop decoupling gain coefficients corresponding to the companion controllers specified in the LD Companions parameter. These coefficients (Mi) are used in the following equation to calculate the loop decoupling response within the Antisurge Controller:


LD Status

This parameter gives the value of the Status parameter from each of the companion Loop Decoupling Controllers.


LD Status LTOP

This parameter is an LTOP array used to obtain the value of the Status parameter from each of the companion Loop Decoupling Controllers.


LD Valid

This parameter indicates that an Antisurge Controller can be decoupled from another controller. The LD Valid parameter must be On for another controller to obtain the decoupling control variable (CV). For an Antisurge Controller, LD Valid will be On when the controller is running; is not at a high or low clamp; and POC is inactive.


Limit

This parameter indicates that a limiting condition exists within the Antisurge Controller. When the controller has reached a Ps, Pd, or Rc limiting condition, this parameter will be On. It will be Off at all other times.

Refer to Limiting Control Response on page 3-52.

dCVLD Mii 1=

10

∑ CVn CVn 1––( )i⋅=


4-54

Load Share Gain

This parameter is used to specify the load-sharing gain (KLS) of the Antisurge Controller. It is applied to the change in the output of the designated Master Controller to produce the load-sharing response of the Antisurge Controller:

This gain is applied only when the resulting dCVLS is positive (so that it will increase the recycle rate) and the S variable indicates a sufficient danger of surge.

Load Share Gain is set to 0 to turn off load sharing.

Refer to Load Sharing on page 3-64.

Low Clamp

This parameter indicates when the intended valve position (Output) has reached the level specified by the Output Low Limit parameter. Low Clamp is Yes when the Output is at the limit and is No at all other times.


LS Status

This parameter is used in Air Miser applications to obtain the Status from the Load Sharing Performance Controller.

Refer to Maximum Flow on page 3-79.

LS Status LTOP

This parameter is used in Air Miser applications to obtain the Status from the Load Sharing Performance Controller.


Manual Auto

This parameter is used to select between the automatic and manual modes of operation for the Antisurge Controller. When this parameter is set to MANUAL, the controller will enter the Manual state. When it is set to AUTO, the controller is placed in the automatic control mode.


dCVLS KLS CVMC, n CVMC, n-1–( )⋅=

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Manual Fallback Enable

This parameter is used to enable a fallback to manual operation when a run freeze fallback has occurred. After the controller has entered a run freeze fallback and has set its output to a default or filtered value, it will switch to manual operation when this parameter is set to On. The user can then manually adjust the Output of the controller.


Manual Override

This parameter allows the user to disable the surge protection features of the controller and manually manipulate the antisurge valve.

Warning! Enabling Manual Override is not recommended because it leaves the compressor unprotected from surge.

When Manual Override is Off, the user can manually move the antisurge valve while still protecting the compressor from surge. The Antisurge Controller will restore automatic operation to protect the compressor from surge if the user manually positions the antisurge valve such that the operating point moves to the left of the Recycle Trip Line (RTL).

Setting Manual Override to On overrides this safety feature. The controller will not protect the compressor from surge if the antisurge valve is manually moved to the left of the RTL. The controller will also ignore Stop and Idle requests.


Manual Rate Close

This parameter is used to specify the rate of change of the Antisurge Controller manual output in the close direction. It is entered as a floating-point number between 0 and 1, which corresponds to a valve opening output change of 0 to 100 percent per second.



4-56

Manual Rate Open

This parameter is used to specify the rate of change of the Antisurge Controller manual output in the open direction. It is entered as a floating-point number between 0 and 1, which corresponds to a valve opening output change of 0 to 100 percent per second.


Manual Target

This parameter is used to manually position the antisurge valve. It is entered as a floating-point number between 0 and 1, which corresponds to the desired position of the valve between 0 and 100 percent. It can be adjusted using the Up and Down inputs while in the Manual state.


Master

This parameter is used within the Antisurge Controller to designate the location of the Master Performance Controller for the load sharing and Pressure Override Control (POC) functions.

The module address for a Master controller uses the following format:

00 XX YY ZZ

where:





For example, if the Master parameter is set to 00010203, the Master controller will be the third ASP of the second module in group 1.

Refer to Pressure Override Control on page 3-60 and Load-Sharing Response on page 3-65.

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Master b Enable

This parameter is used to obtain the Safety Margin (b) from a remote source. When this parameter is set to On, the Safety Margin (b) can be obtained from a remote location using the Master b LTOP parameter. This overrides all other safety margin functions (SO Initial, SO Bias, SO b4).

Master b LTOP

This parameter is used to obtain the Safety Margin (b) from a remote source. When the Master b Enable parameter is set to On, the Safety Margin (b) can be obtained from a remote location using the Master b LTOP parameter.

Master CV LTOP

This parameter is an LTOP array used to obtain the control variable of the Master Performance Controller used in the calculation of the load-sharing response.

Refer to Load-Sharing Response on page 3-65.

Master Status

This parameter is used by the Antisurge Controller to obtain the Status value from the Master Performance Controller through either the Master Status LTOP or through the data packets (Master).

Refer to Pressure Override Control on page 3-60.

Master Status LTOP

This parameter is used to obtain the value of the Status parameter from the Master Performance Controller.


Max +dPd

This parameter contains the maximum positive derivative of the Pd signal recorded during a surge test. This value is used to set the threshold limit (Pd Rate) used in the EAS algorithm.

Note: Max +dPd should be set to zero before conducting surge tests.



4-58

Max +dPo

This parameter contains the maximum positive derivative of the flow signal (recorded during a surge test. This value is used to set the threshold limit (dPo Rate) used in the EAS algorithm.

Note: Max +dPo should be set to zero before conducting surge tests.


Max -dPd

This parameter contains the maximum negative derivative of the Pd signal recorded during a surge test. This value is used to set the threshold limit (Pd Rate) used in the EAS algorithm.

Note: Max -dPd should be set to zero before conducting surge tests.


Max -dPo

This parameter contains the maximum negative derivative of the flow signal recorded during a surge test. This value is used to set the threshold limit (dPo Rate) used in the EAS algorithm.

Note: Max -dPo should be set to zero before conducting surge tests.


Minimum Flow

This parameter is used to define the minimum flow value above which the compressor is assumed to be running. The Antisurge Controller cannot enter the Starting or Run states until the flow is above the Minimum Flow.

Refer to Automatic Sequencing on page 3-91.

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Minimum Flow Control Enable

This parameter is used to enable the minimum flow control fallback strategy. When this parameter is On, various input failures will cause the controller to calculate the proximity-to-surge variable (Ss) as the ratio of the Minimum Flow Set Point and the suction flow measurement. When this parameter is Off, any condition that would normally trigger the minimum flow control fallback strategy will cause the controller to fall back to manual operation.

Refer to Minimum Flow Fallback on page 3-28.

Minimum Flow Set Point

This parameter is used to specify the flow set point used when the minimum flow control fallback is enabled and active. The controller will calculate the proximity-to-surge variable (Ss) as the ratio of the dPosmin (Minimum Flow Set Point) and the suction flow measurement, dPos (dPo Used):

Refer to Minimum Flow Fallback on page 3-28.

Minimum Pressure

This parameter is used to define the minimum discharge pressure value above which the compressor is assumed to be running. The Antisurge Controller cannot enter the Starting or Run states until the discharge pressure is above the Minimum Pressure.


Minimum Speed

This parameter is used to define the minimum speed value above which the compressor is assumed to be running. The Antisurge Controller cannot enter the Starting or Run states until the speed is above the Minimum Speed.


Ss

dPosmin

dPos---------------------=


4-60

N

This parameter contains the current value of the compressor speed signal in rpm, after N Span and N Offset have been applied to the input.


N Offset

This parameter is used to specify the offset applied to the compressor speed input from the field transmitter to produce the value of the N parameter.


N Span

This parameter is used to specify the span applied to the compressor speed input from the field transmitter to produce the value of the N parameter.


Net Flow Available

This parameter is used in Air Miser applications to select the method for calculating the user flow (Q User). It is set to On when a net flow measurement on the header is available. The Antisurge Controller will then calculate Q User from the inlet flow, pressure, and temperature. When Net Flow Available is Off, the controller estimates Q User by subtracting an estimated recycle flow rate (Q Recycle) from the mass flow (Flow).

Refer to User Flow and Recycle Flow on page 3-79.

Not Running

This parameter is set to On when the Antisurge Controller is shut down. It can be used by other controllers as a stop input (through the configuration of the Digital Inputs (2) LTOP array).


Numerator

This parameter gives the current value of the numerator used in the calculation of the proximity-to-surge variable (Ss).


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Numerator Mode

This parameter is used to specify the numerator variable (Y) used in the calculation of the proximity-to-surge variable (Ss):

The numerator modes are listed in the following table.


Output

This parameter gives the current output of the Antisurge Controller. It is a floating-point number between 0 and 1, corresponding to a valve opening of 0 to 100 percent. The Output is dependent on the value of the Output Reverse parameter.

Refer to Output Reverse on page 3-77.

Output High Limit

This parameter is used to specify the maximum allowable output (Output) of the Antisurge Controller. This output clamp is applied after the flow characterizer and valve dead-band bias functions, but before the tight shutoff and output reverse functions. It is inactive when the controller is in the manual control mode. When the Output reaches the Output High Limit, the High Clamp parameter will be On.

The value for the Output High Limit should be entered in percent open, regardless of whether the valve is a fails-open or fails-closed type.


Ss K f1 Z1( ) f2 Z2( ) YX----⋅ ⋅ ⋅=

Name Numerator Mode (Y) Description

S CONTROL S control (see page 3-69)DPC Y = ∆pc pressure rise across the

compressor HP RED Y = hp reduced polytropic head

FUNC RC Y = f6(Rc) function of compression ratio

FUNC HP Y = f6[f3(a) · hp] selected function (a) and reduced polytropic head

FUNC HP TS Y = f6[f3(a) · Ts · hp] / Ts selected function (a), reduced polytropic head, and suction temp


4-62

Output Low Limit

This parameter is used to specify the minimum allowable output (Output) of the Antisurge Controller. This output clamp is applied after the flow characterizer and valve dead-band bias functions, but before the tight shutoff and output reverse functions. It is inactive when the controller is in the manual control mode. When the Output reaches the Output Low Limit, the Low Clamp parameter will be On.

The value for the Output Low Limit should be entered in percent open, regardless of whether the valve is a fails-open or fails-closed type.


Output Reverse

This parameter is used to configure the Antisurge Controller for either a signal-to-open (fails-closed) or signal-to-close (fails-open) antisurge valve. For a signal-to-open valve, this parameter should be set to NORMAL. For a signal-to-close valve, it should be set to REVERSE. The Output Reverse function also applies to the output during manual operation.

Refer to Output Reverse on page 3-77.

Output Tracking Rate

This parameter is used to specify the rate at which the CV Total will ramp toward the Control Override SP (in repeats per minute) when the Control Override function is active.


P Offset

This parameter is used to specify the offset applied to the output of the Cold Recycle (S) Controller to make sure that the cold recycle valve opens first.


Pd

This parameter contains the current value of the discharge pressure signal, expressed in kPa, after Pd Span and Pd Offset have been applied to the input.

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Pd DGO Switch Level

This parameter is used to specify the switch level of the discharge pressure DGO. When the discharge pressure (Pd) exceeds the value of Pd DGO Switch Level, the Pd Level Switch digital output is set to On. It is set to Off when the following condition is met:

Pd < [Pd DGO Switch Level – (Pd * 0.005)]

Pd Limit Enable

This parameter is used to enable discharge pressure limiting control. When this parameter is set to On, the discharge pressure limiting control loop will be active when the value of Pd exceeds the level specified by the Pd Limit SP parameter. If the discharge pressure transmitter fails, this limiting control will be disabled.


Pd Limit SP

This parameter is used to specify the set point for discharge pressure limiting control. When discharge pressure limiting is enabled and active, changes in the control response are calculated by the general PID algorithm using Pd as the process variable, Pd Limit SP as the set point, and Pd Span as the span:

Pd Limit SP is not stored in nonvolatile RAM and is always set equal to Pd Limit SP Default when the controller is powered-up. Once the controller is running, Pd Limit SP can be temporarily changed by setting it to a new value. To permanently change and retain it, both Pd Limit SP and Pd Limit SP Default must be set to the desired value.


Pd Limit SP Default

This parameter is used to specify the default set point for discharge pressure limiting control. When the Antisurge Controller is powered-up, Pd Limit SP is set to the value of the Pd Limit SP Default parameter. Once the controller is running, a new value for Pd Limit SP can be entered.


e Pd Pd Limit SP–Pd Span

--------------------------------------------=


4-64

Pd Limit Status

This parameter indicates the current status of the discharge pressure limiting control loop, as listed in the following table.

Refer to Discharge Pressure Limiting on page 3-54.

Pd Offset

This parameter is used to specify the offset applied to the discharge pressure input from the field transmitter to produce the value of the Pd parameter.


Pd PID DZ

This parameter is used to specify the dead zone for discharge pressure limiting control PID loop, in SI units. It defines the minimum control variable deviation from the Pd Limit SP value that will produce a change in the controller output. This dead zone can be disabled by setting Pd PID DZ to zero.

Refer to PID Dead Zone on page 3-39 and Discharge Pressure Limiting on page 3-54.

Pd PID Kd

This parameter is used to specify the derivative gain (Kd) for the discharge pressure limiting control PID loop.

Refer to General PID Algorithm on page 3-37 and Discharge Pressure Limiting on page 3-54.

Pd PID Ki

This parameter is used to specify the integral gain (Ki) for the discharge pressure limiting control PID loop.


Pd Limit Status Description

DISABLED limiting control loop OffINACTIVE limiting control loop out of limit conditionACTIVE limiting control loop in limit conditionDECAYING limiting control loop ramping down after limit condition

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Pd PID Kp

This parameter is used to specify the proportional gain (Kp) for the discharge pressure limiting control PID loop.


Pd PID Tf

This parameter is used to specify the time filter for the discharge pressure limiting control PID loop.


Pd Rate

This parameter is used to specify the threshold for the discharge pressure derivative signal when a pressure-based Emergency Antisurge mode (EAS Mode) is selected.

This value can be entered as either a positive or negative floating-point number. A positive value specifies that the discharge pressure derivative signal must exceed this value before the Surge Count parameter is incremented. A negative value specifies that the discharge pressure derivative signal must be more negative than this value to increment the Surge Count parameter.

As an aid to setting this rate-of-change threshold, the controller records the most positive discharge pressure derivative in Max +dPd and the most negative flow derivative in Max -dPd. An appropriate Pd Rate can be determined by setting these parameters to zero before surge testing the compressor.



4-66

Pd Samples

This parameter is used to specify the number of samples used by the Emergency Antisurge (EAS) algorithm to determine the discharge pressure derivative. It can be set to the values listed in the following table.



Pd Span

This parameter is used to specify the span applied to the discharge pressure input from the field transmitter to produce the value of the Pd parameter.


PID Velocity High Limit

This parameter is used to specify the maximum allowable rate-of-change of the output (dCV) in the positive (valve open) direction for the antisurge and limiting PID control loops within the Antisurge Controller. It is expressed in percent of PID output change per second.

Refer to PID Velocity Clamps on page 3-40.

PID Velocity Low Limit

This parameter is used to specify the maximum allowable rate-of-change of the output (dCV) in the negative (valve close) direction for the antisurge and limiting PID control loops within the Antisurge Controller. It is expressed in percent of PID output change per second.

Refer to PID Velocity Clamps on page 3-40.

Pis

This parameter contains the current value of the interstage pressure, expressed in kPa, after Pis Span and Pis Offset have been applied to the input.

Value Pd Samples

4 SAMPLES 4

8 SAMPLES 8

c SAMPLES 12

10 SAMPLES 16

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Pis Offset

This parameter is used to specify the offset applied to the interstage pressure input from the field transmitter to produce the value of the Pis parameter.


Pis Span

This parameter is used to specify the span applied to the interstage pressure input from the field transmitter to produce the value of the Pis parameter.


POC

This parameter indicates a POC response has been triggered within the Master Performance Controller, and that the POC Valid parameter within the Master is On. When POC is On, the change in the POC control variable (dCVPOC) from the Master Controller will then be included in the dCV selection within the Antisurge Controller.


POC CV

This parameter gives the value of the POC control variable from the Master Performance Controller.


POC CV LTOP

This parameter is an LTOP array used to designate the location of POC CV within the Master Performance Controller.


POC dCV

This parameter gives the value of the POC delta control variable, which is the sum of the POC control variable from the Master and the filtered POC response (dCVPd).

Refer to Pressure Override Control on page 3-60 and Filtered POC Response on page 3-62.


4-68

POC Enable

This parameter is used to enable the Pressure Override Control (POC) function within the Antisurge Controller. It is set to On to enable the POC function and is set to Off at all other times.


POC Filtered Delta

This parameter gives the current difference between the discharge pressure (pd) and a filtered discharge pressure value (pd, filter). When this difference exceeds a specified threshold (POC Filtered Threshold), a filtered POC response (dCVpd) will result.

The POC Filtered Delta Max parameter gives the maximum value of the POC Filtered Delta which has occurred.


POC Filtered Delta Max

This parameter gives the maximum value of the POC Filtered Delta which has occurred. POC Filtered Delta is the difference between the discharge pressure and a filtered discharge pressure value. POC Filtered Delta Max can be reset to zero.


POC Filtered Gain

This parameter is used to adjust the strength of the discharge pressure filtered POC response.


POC Filtered Threshold

This parameter is used to specify the POC filtered threshold. When the difference between the discharge pressure (pd) and a filtered discharge pressure value (pd, filter) exceeds this threshold, a filtered POC response (dCVpd) will result.


POC PV Tf

This parameter is used to specify the time constant for the discharge pressure filtered POC response.


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POC Status

This parameter gives the current status of the Pressure Override Control (POC) function within the Antisurge Controller, as listed in the following table.


Pos

This parameter gives the current position of the antisurge valve. The valve position is given as a floating-point number between 0 and 1, which corresponds to a valve position between 0 and 100 percent open.

Refer to Recycle Valve Position Feedback on page 3-78.

Pos Delta Delay

This parameter is used to specify the amount of time before a position-output-delta alarm will be generated. When the difference between the position of the antisurge valve (Pos) and the output of the controller (Output) exceeds the value specified by the Pos Delta Max parameter for this amount of time, an alarm will be generated.


Pos Delta Max

This parameter is used to specify the maximum allowable difference between the position of the antisurge valve (Pos) and the output of the controller (Output). When this difference exceeds Pos Delta Max for the amount of time specified by the Pos Delta Delay parameter, an alarm will be generated.


POC Status Description

DISABLED POC disabledINACTIVE POC inactiveACTIVE POC activeDECAYING POC output ramping down after POC active


4-70

Pos Feedback Reverse

This parameter is used to reverse the position feedback (Pos) from the recycle valve to make it correspond to the actual valve position. For a recycle valve or transmitter that is reversed (0 corresponds to fully open and 1 corresponds to fully closed), this parameter would be set to Reverse. Otherwise, it would be set to Normal.


Power EU

This parameter is used to convert power values from kilowatts to another unit of measure for display on an OIM or OIS. The conversions available in the controller are given in the following table.


Pressure Channel

This parameter is used to designate the analog input channel for the pressure signal to be used in mass flow calculations. It is set to one of the inputs listed in the following table.



0 kW kilowatts (no conversion)

1 MW megawatts

2 hp horsepower

3 Amp amperes

Value Pressure Channel Description

– DISABLED

3 PS suction pressure

4 PD discharge pressure

5 PVI inlet valve pressure

6 PIS interstage pressure

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Pressure EU and Pressure2 EU



Pressure Rate EU

This parameter is used to convert pressure rate values from kilopascals per second to another unit of measure for display on an OIM or OIS. The conversions available in the controller are given in the following table.



0 kPa kilopascals (no conversion)

1 bar bars



4 atmS atmospheres






10 barg bars gauge


12 mbar millibars


0 kPa/s kilopascals/second (no conversion)

1 bar/s bars/second

2 psia/s pounds/square inch absolute/second

3 psig/s pounds/square inch gauge/second

4 atmS/s atmospheres/second

5 N/m2/s Newtons/square meter/second

6 inH2O/s inches of water/second

7 kg/cms kilograms/square centimeter/second

8 atmT/s atmospheres/second

9 mmH2O/s millimeters of water/second

10 barg/s bars gauge/second

11 kg/cm2sg kilograms/square centimeter gauge/second

12 mbar/s millibars/second


4-72

Pressure->Flow Time Lag

This parameter is used in EAS surge detection when the EAS Mode parameter is configured to DPO AND PD. When this mode is selected, both the flow derivative and the discharge pressure derivative must exceed their respective thresholds (dPo Rate and Pd Rate) for an EAS surge detection to occur.

An EAS will be detected if the discharge pressure derivative exceeds Pd Rate within the time configured by Pressure->Flow Time Lag after the flow derivative has exceeded dPo Rate.


Pressure2 EU

See description for Pressure EU and Pressure2 EU.

Ps

This parameter contains the current value of the suction pressure signal, expressed in kPa, after Ps Span and Ps Offset have been applied to the input.

Ps DGO Switch Level

This parameter is used to specify the switch level of the suction pressure DGO. When the suction pressure (Ps) goes below the value of Ps DGO Switch Level, the Ps Level Switch digital output is set to On. It is set to Off when the following condition is met:

Ps > [Ps DGO Switch Level – (Ps · 0.005)]

Ps Limit Enable

This parameter is used to enable suction pressure limiting control. When Ps Limit Enable is set to On, the suction pressure limiting control loop will be active when the value of Ps goes below the level specified by the Ps Limit SP parameter. If the suction pressure transmitter fails, limiting control will be disabled.

Refer to Suction Pressure Limiting on page 3-53.

Ps Limit PV

This parameter gives the value of suction pressure limiting process variable.


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Ps Limit SP

This parameter is used to specify the set point for suction pressure limiting control. When suction pressure limiting is enabled and active, changes in the control response are calculated by the general PID algorithm using Ps Limit PV as the process variable, Ps Limit SP as the set point, and Ps Span as the span:

Ps Limit SP is not stored in nonvolatile RAM and is always set equal to Ps Limit SP Default when the controller is powered-up. Once the controller is running, Ps Limit SP can be temporarily changed by setting it to a new value. To permanently change and retain it, both Ps Limit SP and Ps Limit SP Default must be set to the desired value.


Ps Limit SP Default

This parameter is used to specify the default set point for suction pressure limiting control. When the Antisurge Controller is powered-up, Ps Limit SP is set to the value of the Ps Limit SP Default parameter. Once the controller is running, a new value for Ps Limit SP can be entered.


Ps Limit Status

This parameter indicates the current status of the suction pressure limiting control loop, as listed in the following table.


Ps Offset

This parameter is used to specify the offset applied to the suction pressure input from the field transmitter to produce the value of the Ps parameter.


e Ps Ps Limit SP–Ps Span

--------------------------------------------=

Ps Limit Status Description



4-74

Ps PID DZ

This parameter is used to specify the dead zone for suction pressure limiting control PID loop, in SI units. It defines the minimum control variable deviation from the Ps Limit SP value that will produce a change in the controller output. This dead zone can be disabled by setting Ps PID DZ to zero.

Refer to PID Dead Zone on page 3-39 and Suction Pressure Limiting on page 3-53.

Ps PID Kd

This parameter is used to specify the derivative gain (Kd) for the suction pressure limiting control PID loop.

Refer to General PID Algorithm on page 3-37 and Suction Pressure Limiting on page 3-53.

Ps PID Ki

This parameter is used to specify the integral gain (Ki) for the suction pressure limiting control PID loop.


Ps PID Kp

This parameter is used to specify the proportional gain (Kp) for the suction pressure limiting control PID loop.


Ps PID Tf

This parameter is used to specify the time filter for the suction pressure limiting control PID loop.


Ps Span

This parameter is used to specify the span applied to the suction pressure input from the field transmitter to produce the value of the Ps parameter.


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Purge

This parameter is used to request a purge of the compressor. When Purge Enable is On, setting Purge to On will transfer the controller from the Shutdown state to the Purge state. Setting Purge to Off will transfer the controller to the Idle state.

Refer to Purge State on page 3-87.

Purge Enable

This parameter allows the Purge operating state to be selected. When the Purge Enable and Stop Enable parameters are On, the Antisurge Controller will transfer from the Shutdown state to the Purge state when any of the following conditions are met:

■ asserting any Purge digital input;

■ setting the Purge parameter; or

■ any secondary Valve Sharing Controller is in the Purge state, provided the Series parameter for the Primary Valve Sharing Controller is set to On.


Purge Rate

This parameter is used to specify the rate at which the antisurge valve will close when the controller enters the Purge state.


Pvi

This parameter gives the current value of the pressure signal, expressed in kPa, upstream of the inlet valve restriction after Pvi Span and Pvi Offset have been applied to the input.

Pvi Offset

This parameter is used to specify the offset applied to the suction pressure measurement upstream of an inlet valve restriction to produce the value of the Pvi parameter.



4-76

Pvi Span

This parameter is used to specify the span applied to the suction pressure measurement upstream of an inlet valve restriction to produce the value of the Pvi parameter.


Q Max

This parameter is used in Air Miser applications to give the calculated value of the maximum airflow that the compressor can deliver under current operating conditions.

Q Max = CQ Max · fQ Max(pd)


Q Max Characterizer

This parameter is used in Air Miser applications to define the maximum flow characterizer for calculating maximum airflow (Q Max) of the compressor. This characterizer is based on the discharge pressure.

This characterizer is entered into the controller as 10 data pairs consisting of the argument X and the function f(x). The controller uses linear interpolation to calculate intermediate values of the characterizer f(x). Normal values for the f(x) characterizer should be positive floating-point numbers.


Q Max Coefficient

This parameter is used in Air Miser applications to scale the value of the coefficient for calculating the maximum airflow (Q Max) of the compressor.


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Q Rec Out Characterizer

This parameter is used in Air Miser applications to define the flow characterizer for calculating an estimated recycle air flow from the compressor. This flow characterizer is used in the calculation of the recycle flow (Q Recycle) when the Net Flow Available parameter is Off. It uses Display Output as the argument.



Q Rec Rc Characterizer

This parameter is used in Air Miser applications to define the flow characterizer for calculating the recycle flow (Q Recycle) from the compressor. It uses Rc as the argument.



Q Recycle

This parameter gives the calculated air flow through the recycle valve, in Air Miser applications. When the Net Flow Available parameter is Off, the user flow (Q User) is calculated by subtracting the recycle flow (Q Recycle) from the mass flow (Flow):

Q User = Flow – Q Recycle



4-78

Q User

This parameter gives the current airflow to the user, in Air Miser applications. The setting of the Net Flow Available parameter determines the method for calculating Q User. When Net Flow Available is On, Q User is calculated from the mass flow formula. If it is Off, Q User is calculated by subtracting an estimated recycle flow rate (Q Recycle) from the mass flow (Flow).


Q User Coefficient

This parameter is used in Air Miser applications to specify the value of the flow-scaling coefficient used in the calculation of the user flow (Q User).

Note: When specifying the value of C Q User , the user must calculate a value consistent with the pressure and temperature units used in the equation.


R

This parameter gives the current value of the calculated series load-balancing variable used in series load-sharing applications. The Antisurge Controller calculates this parameter based on the total mass flow rate squared:

Refer to Mass Flow Rate on page 3-22 and Load-Balancing Response on page 3-67.

RB Companions

This parameter is an array of 10 module addresses used to designate the companion recycle-balancing Antisurge Controllers in a parallel compressor application. Each element of the array is set equal to the module address of a recycle-balancing companion controller. Unneeded elements must be set to zero. Setting all of the elements in the array to zero disables this feature.


R W2 β5∆po po⋅

To--------------------

= =

April 20, 1998

4-79

00 XX YY ZZ

where:





For example, if an RB Companions element is set to 00010203, the companion controller will be the third ASP of the second module in group 1.

Refer to Recycle Balancing Response on page 3-67.

RB CV LTOP

This parameter is an LTOP array used to obtain the CV Total from each companion recycle-balancing Antisurge Controller.


RB Rate

This parameter is used to specify the rate at which the antisurge valve will open when the recycle-balancing control response is selected. The recycle-balancing control response (dCVRB) has a constant value defined by RB Rate.

Note: The antisurge valve will close at a rate determined by the normal PI response.


RB Valid

This parameter is passed from each companion recycle-balancing Antisurge Controller to indicate that the CV Total from the controller is valid and can be used in the signal-selection of the Max CV Total.



4-80

RB Valid LTOP

This parameter is an LTOP array used to receive the value of the RB Valid parameter from the companion recycle-balancing Antisurge Controllers.


Rc

This parameter gives the current value of the pressure ratio across the compressor, calculated as the ratio of the discharge and suction pressures:

Refer to Compression Ratio on page 3-20.

Rc Limit Enable

This parameter is used to enable compression ratio limiting control. When Rc Limit Enable is set to On, the Rc limiting control loop will be active when the value of Rc exceeds the level of the Rc Limit SP parameter. If a suction or discharge pressure transmitter fails, limiting control will be disabled.

Refer to Compression Ratio Limiting on page 3-55.

Rc Limit SP

This parameter is used to specify the set point for compression ratio limiting control. When compression ratio limiting is enabled and active, changes in the control response are calculated by the general PID algorithm using Rc as the process variable, Rc Limit SP as the set point, and Rc Span as the span:

Rc Limit SP is not stored in nonvolatile RAM, and is always set equal to Rc Limit SP Default when the controller is powered-up. Once the controller is running, Rc Limit SP can be temporarily changed by setting it to a new value. To permanently change and retain it, both Rc Limit SP and Rc Limit SP Default must be set to the desired value.


Rc

pd

ps------=

e Rc Limit Sp Rc–Rc Span

--------------------------------------------=

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Rc Limit SP Default

This parameter is used to specify the default set point for compression ratio limiting control. When the Antisurge Controller is powered-up, Rc Limit SP is set to the value of the Rc Limit SP Default parameter. Once the controller is running, a new value for Rc Limit SP can be entered.


Rc Limit Status

This parameter indicates the current status of the compression ratio limiting control loop, as listed in the following table.

Refer to Compression Ratio Limiting on page 3-55.

Rc PID DZ

This parameter is used to specify the dead zone for compression ratio limiting control PID loop, in SI units. It defines the minimum control variable deviation from the Rc Limit SP value that will produce a change in the controller output. This dead zone can be disabled by setting Rc PID DZ to zero.

Refer to PID Dead Zone on page 3-39 and Compression Ratio Limiting on page 3-55.

Rc PID Kd

This parameter is used to specify the derivative gain (Kd) for compression ratio limiting control PID loop.

Refer to General PID Algorithm on page 3-37 and Compression Ratio Limiting on page 3-55.

Rc PID Ki

This parameter is used to specify the integral gain (Ki) for compression ratio limiting control PID loop.


Rc Limit Status Description



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Rc PID Kp

This parameter is used to specify the proportional gain (Kp) for compression ratio limiting control PID loop.


Rc PID Tf

This parameter is used to specify the time filter for the compression ratio limiting control PID loop.


Rc Span

This parameter is used to specify the span applied to the compression ratio to produce the value of the Rc parameter.


Recycle Trip Test

This parameter is used to request a test of the Recycle Test response. A single, maximum Recycle Trip step response (RT Max Amplitude) will be initiated by setting this parameter to On.

Refer to Recycle Trip Response on page 3-42.

Remote Low Clamping

This parameter indicates the current status of the remote output clamping function. The Antisurge Controller can use the output of another controller as a low clamp for its Output. Remote Low Clamping is On when remote clamping is active, and is Off at all other times.


RT

This parameter indicates the status of the Recycle Trip (RT) control algorithm within the Antisurge Controller. It is On when the RT algorithm is generating RT control responses.


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RT Count

This parameter gives the number of Recycle Trip (RT) responses which have occurred.


RT Deadtime

This parameter is used to specify the amount of time (in seconds) separating successive Recycle Trip (RT) step changes in the Antisurge Controller output. Recycle Trip step changes will continue to be added at the intervals defined by this parameter as long as the operating point is to the left of the RTL.


RT Derivative Response Enable

This parameter is used to enable and disable the derivative portion of the Recycle Trip (RT) control response. When this parameter is On, the RT control response will include the derivative term (KdRT · dSs/dt).

Refer to Recycle Trip Derivative Response on page 3-44.

RT Distance

This parameter is used to configure the distance between the Recycle Trip Line (RTL) and the Surge Control Line (SCL). This distance is determined by applying the f4 control line characterizing function to the specified value of the RT Distance parameter:

RT Distance · f4(Z4)

Refer to Recycle Trip Line on page 3-11.

RT dSs Delay

This parameter is used to specify the Recycle Trip dSs response delay, in seconds. If dSs/dt is greater than the RT dSs Level for an amount of time greater than the RT dSs Delay, the recycle valve will step open by the amount of the RT dSs Response.


Refer to Recycle Trip dSs Response on page 3-45.


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RT dSs Level

This parameter is used to specify the level that the Ss derivative (dSs/dt) must exceed to initiate a Recycle Trip response. When this level is exceeded for the amount of time specified by the RT dSs Delay parameter, the Antisurge Controller will step the recycle valve open by the amount specified by the RT dSs Response parameter.



RT dSs Response

This parameter is used to specify the size of the Recycle Trip dSs response. This response will be triggered when the value of dSs/dt exceeds the value of RT dSs Level for an amount of time greater than RT dSs Delay.



RT Kd

This parameter is used to specify the derivative gain (KdRT) used in calculating the Recycle Trip derivative response:


RT Kp

This parameter is used to specify the proportional gain (KpRT) used in the calculation of the Recycle Trip derivative response:


dCVRT Max= RT KpRT devRT⋅ KdRT+td

dSs⋅

dCVRT Max= RT KpRT devRT⋅ KdRT+td

dSs⋅

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RT Max Amplitude

This parameter is used to specify the maximum step size of the Recycle Trip control response (MaxRT).


RT Status

This parameter indicates the current status of the Recycle Trip control function within the Antisurge Controller, as listed in the following table.

Refer to Recycle Trip Status on page 3-47.

Running

This parameter indicates the run status of the compressor. The controller determines if the compressor is running by comparing the following process variables to the indicated thresholds:

■ the discharge pressure is compared to the value specified by the Minimum Pressure parameter;

■ the main flow measurement (∆po) is compared to the value specified by the Minimum Flow parameter; and

■ the rotational speed (N) is compared to the value specified by the Minimum Speed parameter.

The Running parameter will be On if all of those variables have exceeded their thresholds for the number of seconds specified by the Startup Time parameter. Running will be Off if any of them falls below its threshold for the number of seconds specified by the Stop Time.


S

This parameter gives the current value of the S variable, which is essentially the position of the operating point line relative to the Surge Control Line (SCL), and is calculated as:

S = Ss + Safety Margin = Ss + b · f4(Z4)

Refer to Operating Point on page 3-12.

RT Status Description

INACTIVE Recycle Trip inactiveACTIVE Recycle Trip activeDECAYING Recycle Trip output ramping down after Recycle Trip active


4-86

S Calc Updated

This parameter is incremented every time a parameter which affects the calculation of the S variable is changed.

S Control Start Level

This parameter is used to specify the starting output level of the S Controller output. When the S Controller is shut down and the ESD signal from a Series 4 Speed Controller is Off, the S Controller Output will jump to this level.


S Control Start Speed

This parameter is used to specify the start speed level for the S Controller. If the S Controller is shut down and the speed (N) from a Series 4 Speed Controller exceeds this level, the S Controller Output will start ramping toward the Output High Limit at the specified Start Rate.


S Control Stop Speed

This parameter is used to specify the stop speed level for the S Controller. If the S Controller is shut down and the ESD signal from a Series 4 Speed Controller is set to On, the S Controller Output will go to the Output Low Limit when the speed (N) from the Speed Controller drops below this level.


S Controller Companions

This parameter is an array of 10 module addresses used in a Cold Recycle (S) Controller to designate the hot-recycle companion controllers. Each element of the array is set equal to the module address of a companion controller. Unneeded elements must be set to zero. Setting all of the elements in the array to zero disables this feature.


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4-87

00 XX YY ZZ

where:





For example, if an S Controller Companions element is set to 00010203, the companion controller will be the third ASP of the second module in group 1.


S Failure

This parameter is set to On when there is a failure of any variable used in the calculation of S, in the absence of any fallback values for the variables. The controller will enter a run freeze fallback when S Failure is On.


S Tf

This parameter is used to specify the filter time constant for the calculated value of the proximity-to-surge variable, Ss, and for dSs/dt. This first-order-lag software filter is used to reduce the effects of signal noise.

Refer to Proximity to Surge on page 3-1 and Derivative Response on page 3-41.

Selected I

This parameter gives the value of the integral term (dCVI) from the secondary Valve Sharing controller with the greatest change in its proportional term. This value is used by the primary Valve Sharing Controller in the calculation of its valve-sharing response (dCVVS).



4-88

Selected P

This parameter gives the value of the proportional term (dCVP) from the secondary Valve Sharing controller with the greatest change in its proportional term. This value is used by the primary Valve Sharing Controller in the calculation of its valve-sharing response (dCVVS).


Series

This parameter is used to select either series or parallel valve sharing. It is set to Series to select series valve sharing, and is set to Parallel to select parallel valve sharing.


Shutdown Manual Enable

This parameter is used to allow manual operation while the Antisurge Controller is in the Shutdown operating state. When this parameter is On, the user can manually manipulate the valve in the Shutdown state. When it is Off, manual control can be selected only when the controller is in the Starting, Run, or Remote Run states.


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Side Stream Comp Mode

This parameter is used to define the method the Antisurge Controller will use to calculate the reported flow measurement (dPo Comp), as shown in the following table.

Refer to Reported Flow on page 3-22.

Side Stream Companion

This parameter is used to designate the sidestream companion controller for the Antisurge Controller. It is set equal to the module address of sidestream companion controller. Setting Side Stream Companion to zero disables this feature.


00 XX YY ZZ

where:





Name dPo Comp = Description dPo Measurement

DPOS dPo Calc when the companion controller needs the suction flow measurement (dPos) from the compressor, dPo Calc can be reported without any compensation being applied

Downstream

FUNCT RC dPo Calc · f5(Rc) when the companion controller needs the discharge flow measurement from the compressor, dPo Comp can be calculated by applying a characterizer to dPo Calc, where f5 is defined by f5 Characterizer

Upstream

RC SIGMAdPo Calc · Rc

σ-1when the companion controller needs the discharge flow measurement (dPod) from the compressor, dPo Comp can be calculated from compression ratio and sigma (σ)

Upstream

PRESS TEMP dPo Calc · (T Ratio / Rc) when the companion controller needs the discharge flow measurement (dPod) from the compressor, and the suction and discharge temperatures are measured, dPod can be calculated from the compression and temperature ratios

Upstream


4-90

For example, if Side Stream Companion is set to 00010203, the companion controller will be the third ASP of the second module in group 1.


Sigma

This parameter gives the current value of the calculated polytropic head exponent (σ) used in the Antisurge Controller surge protection and load-sharing algorithms:

Refer to Polytropic Head Exponent on page 3-21.

Sigma Tf

This parameter is used to specify the time constant of the first-order-lag software filter applied to the calculated polytropic head exponent, Sigma.

Refer to Polytropic Head Exponent on page 3-21.

SO

This parameter gives the status of the Safety On function within the Antisurge Controller. When a Safety On response is triggered, SO is set to On. SO is reset to Off when the Surge Count Reset parameter is asserted.


SO b4

This parameter is used to specify the value of the additional margin of safety (b4) which is added to the Safety On control response when the Load Sharing Controller is not running and the check valve is open. It is ramped to the value of SO b4 at the rate specified by the SO b4 Rate or Derivative Response Rate parameters, depending on whether b4 is increasing or decreasing.


σTd Ts⁄( )log

pd ps⁄( )log------------------------------=

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4-91

SO b4 Rate

This parameter is used to specify the rate at which the additional margin of safety (b4) is ramped to the value of SO b4 when b4 is increasing. It is ramped to the value of SO b4 when the Load Sharing Controller is not running and the check valve is open.


SO Bias

This parameter is used to specify the value of the Safety On incremental bias. Each time the compressor experiences a surge, the accumulated Safety On bias (b2) is incremented by the SO Bias and added to the initial Safety On margin (SO Initial) to produce an increasing Safety On control response (CRso) with each additional surge detection.


SO Dead Time

This parameter is used to specify the period of time that surge detection is suspended after a surge event. This allows time for the operating point of the compressor to move back to the right of the SOL before another Safety On response is triggered. If the operating point is still to the left of the SOL after the dead time has expired, the Surge Count will be incremented and another Safety On response will be triggered. The SO Time Based Enable parameter must be set to On.


SO Distance

This parameter is used to configure the distance between the Safety On Line (SOL) and the Surge Limit Line (SLL). This distance is determined by applying the f4 control line characterizing function to the specified value of the SO Distance parameter:


Refer to Safety On Line on page 3-11 and Safety On Response on page 3-47.


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SO Initial

This parameter is used to specify the initial Safety On margin (b1), which defines the minimum distance between the SLL and SCL. It is added to the accumulated Safety On bias (b2) to calculate the Safety On control response (CRso). When the Surge Count is zero, CRSO is equal to the initial Safety On margin (SO Initial).

This parameter is also used in the calculation of the Recycle Trip deviation (devRT).

Refer to Recycle Trip Response on page 3-42 and Safety On Response on page 3-47.

SO Time Based Enable

This parameter is used to enable a time-based Safety On response within the Antisurge Controller when the operating point is to the left of the Safety On Line (SOL). After a surge event, if the operating point is still to the left of the SOL when the SO Dead Time has expired, another Safety On response will be triggered.

When SO Time Based Enable is disabled, the operating point must move back to the right of the SLL after a surge event before another Safety On response can be triggered.


Ss

This parameter contains the current value of the proximity-to-surge variable Ss, used in the calculation of Antisurge Controller control responses.

Refer to Proximity to Surge on page 3-1.

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Ss Samples

This parameter is used to specify the number of samples used in the calculation of the Ss derivative, dSs/dt. It can be set to the values listed in the following table.



Start Rate

This parameter is used to specify the rate at which the recycle valve is closed when the Antisurge Controller enters the Starting state.

Refer to Starting State on page 3-88.

Startup Time

This parameter is used to specify the amount of time that the speed, flow, and discharge pressure values must stay above their specified minimum thresholds (Minimum Speed, Minimum Flow, and Minimum Pressure) before the compressor is assumed to be running (Running set to On).


State

This parameter gives the current operating state of the Antisurge Controller. The possible controller operating states are listed in the following table.

Refer to Operating States on page 3-84.

Value Ss Samples

4 SAMPLES 4

8 SAMPLES 8

c SAMPLES 12

10 SAMPLES 16

State Description

SHUTDOWN holds recycle valve fully open

IDLE ramps recycle valve fully open

PURGE ramps recycle valve fully closed

RUN modulates recycle valve to prevent surge and minimize recycling

MANUAL holds recycle valve in position specified by user

REMOTE RUN

for parallel valve sharing, modulates shared recycle valve to protect the compressor of another controller

STARTING closes recycle valve


4-94

Status

This parameter is a bit-mapped array used by other controllers to get status information from the Antisurge Controller.

Stop

This parameter is used to stop the compressor. When this parameter is On, and the request is valid based on the current state of the controller, the Antisurge Controller will transfer to the Shutdown state.


Stop Enable

This parameter is set to On to allow the controller to enter Shutdown, Purge, and Idle operating states. The controller cannot enter these states when this parameter is Off.

Note: There are also other conditions which must be met for the controller to enter the Shutdown, Purge, and Idle states.

Refer to Operating States on page 3-84.

Stop Rate

This parameter is used to specify the rate at which the antisurge valve (and the Display Output) is ramped to the maximum output clamp (Output High Limit) when the Antisurge Controller enters the Idle state, thus fully opening the valve.

Refer to Idle State on page 3-87.

Stop Status

This parameter gives the value of a Stop request from a serial or digital input. It is set to On when the Antisurge Controller has been stopped using the Stop parameter or the Stop digital input. Stop Status is used to allow other controllers to get the condition of the Antisurge Controller directly from this value.


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Stop Time

This parameter is used to specify the amount of time that the speed, flow, or discharge pressure value must stay below its configured minimum threshold (Minimum Speed, Minimum Flow, and Minimum Pressure) before the compressor is assumed to be shut down (Running set to Off).


Suction Pressure EU and Suction Pressure2 EU



Surge Count

This parameter indicates the current number of surge events detected by the controller through the Safety On and EAS functions. The Surge Count is cleared when Surge Count Reset to set to On, or when the Surge Count Shutdown Reset parameter is On and the controller enters the Shutdown state.



0 kPa kilopascals (no conversion)

1 bar bars



4 atmS atmospheres






10 barg bars gauge


12 mbar millibars


4-96

Surge Count Reset

This parameter is used to clear the Surge Count parameter, which has the effect of resetting the Safety On response.

Asserting the Surge Count Reset parameter will also reset the Safety On response (CRSO), reset the SO parameter to Off, reset the accumulated Safety On bias (b2) to zero, and initialize the PID to prevent a bump in the controller output.


Surge Count Shutdown Reset

This parameter is set to On to automatically clear the Surge Count when the Antisurge Controller enters the Shutdown operating state.


Surge DZ

This parameter is used to specify the dead zone for the main antisurge PID control loop, in SI units. It defines the minimum control variable deviation that will produce a change in the controller output. This dead zone can be disabled by setting Surge DZ to zero.

Refer to PID Dead Zone on page 3-39 and Antisurge PI Response on page 3-40.

Surge Ki

This parameter is used to specify the integral gain (Ki) used by the main antisurge PID control loop.

Refer to Antisurge PI Response on page 3-40.

Surge Kp

This parameter is used to specify the proportional gain (Kp) used by the main antisurge PID control loop.

Refer to Antisurge PI Response on page 3-40.

Surge Relay Threshold

This parameter is used to configure the number of surge detections considered excessive for an application. When the Surge Count is greater than or equal to the Surge Relay Threshold, the Exc Surge parameter will be set to On. The Surge digital output is assigned from the value of Exc Surge.


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Surges

This parameter indicates the total number of surge events detected by the controller through the Safety On and EAS functions. Unlike the Surge Count parameter, Surges is not reset to zero using the Surge Count Reset parameter. Surges must be manually set back to zero by writing a 0 to it.


T Air

This parameter is not used in this version of the Antisurge Controller.

T Air Gain


T Air Normal


T CW


T CW Gain


T CW Normal


T Ratio

This parameter gives the current value of the temperature ratio across the compressor:

Refer to Temperature Ratio on page 3-20.

T RatioTd

Ts------=


4-98

Tac

This parameter contains the current value of the aftercooler temperature signal, expressed in Kelvin, after Tac Span and Tac Offset have been applied to the input.

Tac Offset

This parameter is used to specify the offset applied to the aftercooler discharge temperature input from the field transmitter to produce the value of the Tac parameter.


Tac Span

This parameter is used to specify the span applied to the aftercooler discharge temperature input from the field transmitter to produce the value of the Tac parameter.


Td

This parameter contains the current value of the discharge temperature signal, expressed in Kelvin, after Td Span and Td Offset have been applied to the input.

Td DGO Switch Level

This parameter is used to specify the switch level of the discharge temperature DGO. When the discharge temperature (Td) exceeds the value of Td DGO Switch Level, the Td Level Switch digital output is set to On. It is set to Off when the following condition is met:

Td < [Td DGO Switch Level – (Td · 0.005)]

Td Offset

This parameter is used to specify the offset applied to the discharge temperature input from the field transmitter to produce the value of the Td parameter.


Td Span

This parameter is used to specify the span applied to the discharge temperature input from the field transmitter to produce the value of the Td parameter.


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4-99

Temperature Based Hp Enable

This parameter is used to enable the polytropic head fallback strategy. If this parameter is set to On, and either of the pressure inputs normally used to calculate reduced polytropic head (hp) fail, the controller will calculate hp using the temperature ratio (T Ratio) and default σ (Default Sigma) values.

Refer to Polytropic Head Fallback on page 3-29.

Temperature Channel

This parameter is used to designate the analog input channel for the temperature signal to be used in mass flow calculations. It is set to one of the inputs listed in the following table.


Temperature EU and Temperature2 EU

This parameter is used to convert temperature values from Kelvin to another unit of measure for display on an OIM or OIS. The conversions available in the controller are given in the following table.


Value Temperature Channel Description

– DISABLED

7 TS suction temperature

8 TD discharge temperature

9 TAC aftercooler temperature

a TIS interstage temperature


0 K Kelvin (no conversion)

1 C Celsius

2 F Fahrenheit

3 R Rankin


4-100

Tight Shut Off Distance

This parameter is used to configure the distance between the Surge Control Line (SCL) and the Tight Shut-Off Line (TSL). This distance is determined by applying the f4 control line characterizing function to the specified value of the Tight Shut Off Distance parameter:

Tight Shut Off Distance · f4(Z4)

Refer to Tight Shutoff Line on page 3-11 and Tight Shutoff on page 3-76.

Tis

This parameter contains the current value of the interstage temperature signal, expressed in Kelvin, after Tis Span and Tis Offset have been applied to the input.

Tis Offset

This parameter is used to specify the offset applied to the interstage temperature input from the field transmitter to produce the value of the Tis parameter.


Tis Span

This parameter is used to specify the span applied to the interstage temperature input from the field transmitter to produce the value of the Tis parameter.


Track


Ts

This parameter contains the current value of the suction temperature signal, expressed in Kelvin, after Ts Span and Ts Offset have been applied to the input.

Ts Offset

This parameter is used to specify the offset applied to the suction temperature input from the field transmitter to produce the value of the Ts parameter.


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Ts Span

This parameter is used to specify the span applied to the suction temperature input from the field transmitter to produce the value of the Ts parameter.


Up

This parameter is used to manually move the antisurge valve. Each time the Up parameter is asserted, the output from the Antisurge Controller is raised at the rate specified by the Manual Rate Open parameter. The Up parameter is automatically reset to Off after each increment in the output. As a result, the Up parameter must be On each time additional manipulation of the Antisurge Controller output is desired.


User

This parameter contains the current value of the user-defined signal after User Span and User Offset have been applied to the input.

User Offset

This parameter is used to specify the offset applied to the user-defined input from the field transmitter to produce the value of the User parameter.


User Span

This parameter is used to specify the span applied to the user-defined input from the field transmitter to produce the value of the User parameter.


Valve Characterizer

This parameter is used to define the valve characterization data applied to the output value (Output). This data is applied when the Valve Mode parameter is set to 3 (characterization mode).

The valve characterization data is entered as an array of floating point numbers. Each is entered as a value between 0 and 1, which corresponds to a valve open position of 0 to 100


4-102

percent. The controller uses linear interpolation to calculate intermediate values of the function.

The valve characterization data is not applied to a manual output when the controller is in the Manual state.

Refer to Valve Flow Characterization on page 3-73.

Valve Dead Band Bias

This parameter is used to specify the dead-band bias applied to the Antisurge Controller output (Output). This bias is disabled by setting this parameter to zero. The output clamps (Output Low Limit and Output High Limit) are applied to the output after the valve dead band bias.

Refer to Valve Dead-Band Compensation on page 3-75.

Valve Dead Band Bias Threshold

This parameter is used to specify the minimum amount the valve must move after the intended valve position changes direction, before the Valve Dead Band Bias is added.

Refer to Valve Dead-Band Compensation on page 3-75.

Valve Mode

This parameter is used to specify the valve characterization mode for the antisurge valve. The control response of the valve can be set to any of the four values listed in the following table.

The selected mode is applied to the controller output (Output). The valve mode function is not applied when the controller is in the Manual state.

Refer to Valve Flow Characterization on page 3-73.

Valve Mode Description

LINEAR The output calculated by the controller is not altered.

FAST The output is the square of the intended flow rate calculated by the controller.

SLOW The output is the square root of the intended flow rate calculated by the controller.

CHAR The data specified by the Valve Characterizer parameter is applied to the output calculated by the controller.

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Valve Sharing Companions

This parameter is an array of 10 module address used to designate the primary and secondary Valve Sharing Controllers. The primary Valve Sharing Controllers should point to the secondary Valve Sharing Controllers, and vice versa.

Each element of the array is set equal to the module address of a Valve Sharing Controller. Unneeded elements must be set to zero. Setting all of the elements in the array to zero disables this feature.


00 XX YY ZZ

where:





For example, if a Valve Sharing Companions element is set to 00010203, the companion controller will be the third ASP of the second module in group 1.


Valve Sharing Mode

This parameter is used to designate an Antisurge Controller as a primary or secondary Valve Sharing Controller. For stand-alone Antisurge Controllers, the Valve Sharing Mode should be set to Primary.

The module addresses of the secondary Valve Sharing Controllers must also be entered into the Valve Sharing Companions array of the primary Antisurge Controller.



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Variable List

This parameter is used to turn on and turn off the display of input variables on the Operator Interface Module (OIM). Setting an index of this parameter to Off will remove the corresponding variable from the OIM display.

VS

This parameter indicates that a response from a secondary Valve Sharing controller to open the recycle valve has been signal-selected within the primary Antisurge Controller.


VS CV LTOP

This parameter is an LTOP array used within the primary Valve Sharing Controller to obtain the CV values from the secondary Valve Sharing Controllers located in different chassis.


VS I LTOP

This parameter is an LTOP array used within the primary Valve Sharing Controller to obtain the Selected I values from the secondary Valve Sharing Controllers located in different chassis.


VS P LTOP

This parameter is an LTOP array used within the primary Valve Sharing Controller to obtain the Selected P values from the secondary Valve Sharing Controllers located in different chassis.


VS RT

This indicates within a primary Valve Sharing Controller that a Recycle Trip response has been triggered within a secondary Valve Sharing controller. When this occurs, the RT parameter within the primary controller is set to On.


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VS S LTOP

This parameter is an LTOP array used within the primary and secondary Valve Sharing Controllers to obtain the S values from primary and secondary Valve Sharing Controllers located in different chassis.


VS Status

This parameter indicates the current status of the Valve Sharing control function within the Antisurge Controller. The possible values of this parameter are listed in the following table.


VS Status Description

DISABLED Valve Sharing disabledINACTIVE Valve Sharing inactiveACTIVE Valve Sharing activeDECAYING Valve Sharing output ramping down after Valve

Sharing active


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April 20, 1998

Operator Interface Module 5-1

Chapter 5: Operator Interface Module

The Operator Interface Module (OIM) is used to configure, operate, and monitor the Antisurge Controller, the Fault Tolerant Operating System (FTOS), and any other Application Software Packages (ASPs) installed on the IOM. This chapter covers only the Antisurge Controller displays.

The FTOS displays are presented in UM4003, Series 4 Fault Tolerant Operating System, which also includes a physical description of a Series 4 OIM and the following OIM information:

■ selecting the application interface,

■ switching the communication link,

■ changing the OIM access level,

■ entering parameter values with an OIM, and

■ OIM adjustment and diagnostic procedures.

Main ControlScreen

The main control screen for the Antisurge Controller is displayed on the OIM in Figure 5-1 on page 5-2. The user can access this screen in any of the following ways:

■ Press the appropriate function key from an FTOS or Antisurge control screen.

■ Use the Application option on the Antisurge or FTOS Menu Systems.

■ Select the Control Screen option on the Antisurge Menu System.

■ Press CLEAR from an Antisurge control screen or the Antisurge Menu System.

The top line of the main control screen provides information on the current application interface.

The control screen also displays the value of the antisurge Deviation parameter (DEV), which indicates the distance between the operating point of the compressor and the Surge Control Line (SCL). A positive Deviation indicates the operating point is to the right of the SCL. A zero value corresponds to operation on the SCL. A negative Deviation value shows that the operating point is to the left of the SCL,


5-2 Operator Interface Module

indicating an imminent danger of surge (see Surge Control Line on page 3-10).

The OUT display on the main control screen gives the value of the Display Output parameter in percent of span. If the valve dead band compensation function has been enabled (see page 3-75), the OUT value will jump whenever the control action changes direction.

Figure 5-1 Antisurge Controller OIM

The STATUS display indicates the current status of the Antisurge Controller, as given by the Controller Status parameter. The possible values of this display are described below:

∞§∞¶∞¶∞¶∞FTOS AS

ANTISURGE

status: RUN

Run

OSP/Prg ESD/SORdy/C VlvFault

LimitRemoteCrit/TrkAutoStop

Local/RT AlarmManual

COMPRESSOR

CONTROLS

CORPORATION

1

6

∆

∇

F4F1

Idle/Flbk

5

0

MENU

SCROLL

ENTER

4

CLEAR

9

3

8

2

RESET

7SET

POINT

OPMODE

AUTO

MAN

F3F2

LCD

ControlKeys

StatusLEDs

Panel

Antisurge Controller

FunctionKeys

11a/ANTISURGEIOM

DEV ˘001OUT 4˘3

April 20, 1998


■ SHUTDOWN: The controller is holding the recycle valve fully open so any high-pressure gas leaking through the check valve can flow around the compressor.

■ PURGE: The controller is holding the recycle valve fully closed so purge gas can be forced through the compressor.

■ RUN: The compressor is running and the controller is modulating the recycle valve as needed to protect against surge while minimizing the recycle flow rate.

■ TRACKING: The output of the Antisurge Controller is tracking the value of an analog input.

■ MANUAL RUN: The recycle valve is being manually positioned by the user while the compressor is running.

■ MANUAL SD: The recycle valve is being manually positioned by the user while the compressor is shut down.

■ REMOTE RUN: The compressor is shut down but the valve is being modulated to protect the compressor of a Valve Sharing Controller.

■ STOPPING: The recycle valve is being ramped open by the stop sequence.

■ STARTING: The recycle valve is being ramped closed by the start sequence.

■ RUN NEXT SD: In Air Miser applications, the compressor is designated as the next compressor to be shut down by the Master Performance Controller.

■ IDLE: The recycle valve is being ramped open while the compressor is shutting down.

The function key prompts across the bottom of the control screen are used to select the application interface. The prompt for the application currently selected is highlighted.

Pressing SCROLL while the main control screen is displayed will also display the current values of the Safety Margin (b) and the number of surge events (Surge Count), as shown in Figure 5-2.

Note: If any limiting control screens are enabled, they will be displayed before the safety margin and surge information when SCROLL is pressed (see Limiting Control Screens on page 5-4)



.

Figure 5-2 Safety Margin and Surge Count Display

Pressing SCROLL again will remove the safety margin and surge information.

Limiting ControlScreens

In addition to the main control screen, the Antisurge Controller OIM can also display limiting control screens for the suction and discharge pressure limiting control loops, as shown in Figure 5-3.

Figure 5-3 Antisurge Controller Limiting Control Screens

Each limiting control screen can be displayed only if the corresponding loop is enabled by setting the Pd Limit Enable or Ps Limit Enable parameters to On. The user can then cycle through the main and limiting control screens by pressing SCROLL.

Each limiting control screen displays the following additional information:

∞§∞¶∞¶∞¶∞FTOS AS

ANTISURGE

status: RUN

11a/ANTISURGEIOM

DEV ˘001OUT 4˘3safety margin: 0.200

surges: 2

PV 4˘29

SP 3˘50

OUT

4˘3

status:

RUN

∞§∞¶∞¶∞¶∞

FTOS AS

∞§∞¶∞¶∞¶∞

FTOS AS

11a/ANTISURGEIOM

PD LIMIT

PV 78˘3

SP 80˘0

OUT

4˘3

status:

RUN

11a/ANTISURGEIOM

PS LIMIT

April 20, 1998


■

The process variable (PV) readout represents the current discharge or suction pressure.

■

The set point (SP) readout represents the discharge or suction pressure limiting control threshold, specified using the

Pd Limit SP

and

Ps Limit SP

parameters.

■

The OUT display gives the value of the

Display Output

parameter in percent of span.

Control Keys

When an Antisurge Controller main or limiting control screen is displayed, the control keys have the following functions:

■

When the controller is being manually operated, pressing the

∆

(Raise) or

∇

(Lower) key will increase or decrease the

Display Output

.

■

Pressing the AUTO/MAN key toggles the controller between automatic and manual operation. The Auto or Manual LED will light to indicate which mode is selected.

■

Pressing RESET acknowledges all existing alarms and clears those that have been corrected.

■

Pressing the OP MODE key displays prompts for resetting the Safety On surge count or performing a Recycle Trip test (see

Operating Mode Selection

on page 5-9).

■

The SET POINT key is not used by the Antisurge Controller.

■

The ENTER key is used to verify an operating mode selection.

■

Pressing the CLEAR key aborts the operating mode selection procedure, or returns the user to the main control screen.

■

The MENU key displays the Antisurge main menu.

■

Pressing the SCROLL key displays the next available Antisurge control screen, or the safety margin and surge count information.



LEDs

When the Antisurge Controller ASP interface is selected, the LED indicators have the functions summarized in Table 5-1.

Table 5-1 Antisurge Controller LEDs

■

The red Alarm LED will flash whenever a new, unacknowledged alarm condition is detected within the Antisurge Controller. Pressing RESET will acknowledge any new Antisurge Controller alarms, and clear any corrected alarms from the Antisurge Controller alarm buffer. The Alarm LED will remain illuminated, but not flash, when the alarm buffer contains any acknowledged, uncorrected alarms. The LED will be Off only when all alarms are acknowledged and corrected, and the alarm buffer is empty.

Note:

The Alarm LED will also flash and illuminate for FTOS alarms. FTOS alarms must be acknowledged and cleared

from the FTOS application.

Name Color Meaning (On; Flashing)

Alarm RedAcknowledged alarms; New/Unacknowledged alarms

Auto Green Automatic operating state selected

Crit/Trk YellowControl Override active; remote clamp selected

ESD/SO Red Safety On response (surge count > 0)

Fault Red Fatal error; OIM/IOM communication failure

Idle/Flbk YellowOne or more fallback strategies are being used to calculate the deviation

Limit YellowLimiting control response selected; POC control response selected

Local/RT YellowRecycle Trip response active or margin of safety less than RT threshold

Manual YellowManual operating state selected; Manual operating state selected and manual override function active

Run GreenController in Run state; Controller in Starting state

Stop RedController in Shutdown state; Stopping sequence initiated, controller in Idle state

OSP/Prg Red Not used

Rdy/C Vlv Green Not used

Remote Green Not used

April 20, 1998


■

The green Auto LED will be illuminated when the Antisurge Controller is operating automatically. Otherwise, the yellow Manual LED will be illuminated to indicate the controller is being manually operated. Pressing the AUTO/MAN key will toggle between the automatic and manual modes (provided manual operation is enabled).

■

The yellow Crit/Trk LED (Track for this application) will be illuminated when Control Override is active (see page 3-77). This LED will flash when the remote clamp is selected (see page 3-72).

■

If the red ESD/SO LED (SO for this application) is illuminated, the Safety On response (see page 3-47) has detected one or more surge events. This LED will remain illuminated until the surge count is reset using the

Surge Count Reset

parameter.

Note:

If the OIM has been assigned at least an Engineer access level, the Safety On response can also be reset using the OP MODE key, as discussed in

Operating Mode Selection

on

page 5-9.

■ The red Fault LED is illuminated to indicate a fatal error in the IOM, and flashes to indicate that the OIM is unable to communicate with the IOM.

■ The yellow Idle/Flbk LED (Fallback for this application) is illuminated to indicate that one of the fallback strategies within the Antisurge Controller is active. Refer to Fallback Strategies on page 3-27 for more information.

■ The yellow Limit LED will be illuminated when suction or discharge pressure limiting control is enabled (see page 3-52), and one of the pressures goes beyond its limiting control set point (that is, if the discharge pressure is above its control threshold or the suction pressure is below its limit). This LED will flash if the Pressure Override Control response is enabled and selected.

■ The yellow Local/RT LED (RT for this application) will be illuminated when the compressor operating point moves to the left of the Recycle Trip line (RTL, see page 3-11). If the controller is operating automatically, this LED will remain illuminated until the Recycle Trip response (see page 3-42) decays to zero. If the controller is operating manually, this LED will remain illuminated only until the operating point moves back to the right of the RTL.


5-8

Operator Interface Module

■ The yellow Manual LED will be illuminated when the user is manually operating the controller. Otherwise, the green Auto LED will be illuminated to indicate the Antisurge Controller is operating automatically. Pressing the AUTO/MAN key will toggle between the automatic and manual modes (provided manual operation is enabled).

When the controller is in manual and the manual override function is active, the yellow Manual LED will blink.

■ The green Run LED will be continuously illuminated when the controller is in the Run state. It will flash when the controller is in the Starting state.

■ The red Stop LED will be continuously illuminated when the controller is in the Shutdown state. It will flash when the Stopping sequence has been initiated and the controller is in the Idle state.

■ The remaining LEDs are not used by the Antisurge Controller.

April 20, 1998


OperatingMode Selection

When an Antisurge control screen or menu is displayed, and the OIM has been assigned at least an Engineer access level, the following procedure can be used to initiate a Recycle Trip test (see page 3-47) or reset the Safety On surge count (see page 3-47):

Step 1: Press OP MODE to display the operating mode prompts across the bottom of the screen, as shown in the left panel of Figure 5-4.

Step 2: Press the function key corresponding to the desired operating mode. For example, pressing the F1 key selects the Safety On reset. Pressing CLEAR will cancel the operating mode prompts.

Step 3: When the prompt shown in the right panel of Figure 5-4 is displayed, press ENTER to execute the selected action, or CLEAR to cancel it.

Figure 5-4 Operating Mode Prompts

F4F1 F3F2

Ò˜Â„Â„Â„‰RTSO

Ò˜‹„‹„‹„‰Select SO RESET? (Enter/Clear)

11a/ANTISURGEIOM

DEV ˘001OUT 4˘3

11a/ANTISURGEIOM

DEV ˘001OUT 4˘3

RESET TEST



Menu System The Menu System allows the user to perform various configuration, operation, and monitoring functions within the Antisurge Controller. It also enables the user to:

■ view the current values of all physical inputs and outputs;

■ view and configure the operating parameters;

■ view the alarms and event history; and

■ adjust the OIM operation.

The Antisurge Controller main menu, shown in Figure 5-5, can always be displayed by pressing the MENU function key when the Antisurge application is selected. Pressing SCROLL alternately displays the two pages of the menu.

Figure 5-5 Antisurge Main Menu

The top portion of the display gives controller information while the remainder of the panel displays menu prompts.

Unless a numeric value for a configuration parameter is being entered, the control keys have the following functions throughout the Antisurge Menu System:

■ The ∆, ∇ , AUTO/MAN, RESET, OP MODE, SET POINT, and ENTER keys retain their normal functions.

■ Pressing CLEAR cancels the Menu System and restores the Antisurge main control screen. However, within the Configuration and OIM Service submenus, pressing CLEAR cancels the current option and restores the menu from which it was selected.

■ Pressing MENU always displays the Antisurge main menu.

■ If the selected menu or option has more than one prompt screen, pressing SCROLL cycles through them. The page number is displayed in the upper right corner of the menu screen.

MAIN MENU 1 ¡™£¢

Control Screen

Variables

History

Alarms

MAIN MENU 2 ¡ Application

™£

Configuration

OIM Service

Press SCROLL for more Press SCROLL for more

»DEV .001 OUT 4.3RUN

11a/ANTISURGEIOM 11a/ANTISURGEIOM


April 20, 1998


Control Screen Selecting the Control Screen menu option restores the Antisurge main control screen shown in Figure 5-1. The main control screen can also be accessed from the menu system by pressing CLEAR when any menu other than a Configuration or OIM Service submenu is displayed.

Variables Selecting the Variables option from the Antisurge main menu displays the values of the first eight parameters in the InOut group of the Antisurge Controller database, as shown in Figure 5-6. The additional parameters in this group can be displayed by pressing SCROLL.

Figure 5-6 Antisurge Variables Screen

Alarms Selecting the Alarms option displays the Antisurge Controller alarm buffer shown in Figure 5-7.

Figure 5-7 Antisurge Alarm Buffer

The alarm buffer records up to twenty alarms. If there are more than eight alarms in the buffer, the additional alarms can be displayed by pressing SCROLL.

DPO1 0.000 kPa

VARIABLES 1

DPO2 0.000 kPaDPO USED 0.000 kPaDPO DEV offDPO SELECT DPO1PD 101.3 kPaPS 0.000 kPaDPO1 272.0 K

Press SCROLL for more

11a/ANTISURGEIOM


ALARM BUFFER

11a/ANTISURGEIOM




Each time the controller detects an alarm condition that is not already listed, it adds that alarm to the buffer and causes Alarm LED to flash.

Pressing RESET will acknowledge all new and existing alarms recorded in the buffer, and clear those that have been corrected. Those that are not corrected will automatically be removed from the buffer when they are corrected.

The Alarm LED will remain on (not flashing) until all alarms are corrected and cleared from the alarm buffer. The LED will be off only when all of the alarm buffers are empty.

History Selecting the History option displays the Antisurge Controller history buffer shown in Figure 5-8.

Figure 5-8 Antisurge History Buffer

The history buffer records up to twenty events. Each time a new event is detected it is added to the top of the buffer. If there are more than eight events in the buffer, the additional events can be displayed by pressing SCROLL.

If the OIM has been assigned System level access, pressing RESET while the history buffer is displayed will clear the buffer. Events remain in the buffer until cleared or displaced by subsequent events.

Application Selecting the Application option from the Antisurge main menu displays the screen shown in Figure 5-9, from which the application can be changed. Pressing F1 will display the FTOS information screen discussed in UM4003, Series 4 Fault Tolerant Operating System. Pressing F2 will display the Antisurge main control screen shown in Figure 5-1. The control screens for any additional applications installed on the

HISTORY BUFFER

11a/ANTISURGEIOM


April 20, 1998


IOM can be displayed by pressing the corresponding function key.

Figure 5-9 Application Options

Configuration Selecting the Configuration option displays the Configuration menu shown in Figure 5-10 on page 5-14. Pressing SCROLL sequentially displays the six pages of the menu.

The Configuration menu is used to configure the parameters used in the Antisurge Controller. The parameters are listed on the menu by group and subgroup.

When a parameter group is selected from the Configuration menu by pressing the corresponding function key, the first page of the subgroup list is displayed (note that some groups do not have subgroups). Subsequent pages of the subgroup list, if any, can be displayed by pressing SCROLL.

When a parameter subgroup is then selected, the first four parameters in that subgroup are displayed on the OIM. Additional parameters, if any, can be displayed by pressing SCROLL.

APPLICATION ¡

S4 FTOS

™

ANTISURGE

11a/ANTISURGEIOM

»

DEV

.001

OUT

4.3

RUN



Figure 5-10 Antisurge Configuration Menu

For example, selecting the Calculate SCL option from the Configuration menu (F3 on page 1) would display the subgroups shown in the left panel of Figure 5-11. Pressing F3 would then display the parameters in the Char Modes subgroup, as shown in the right panel.

CONFIGURATION 1

™£¢

STATUS

AUTO SEQUENCE

SO & RT

CALCULATE SCL

¡


CONFIGURATION 2

™£

CONTROL

CONFIGURE IO

ENGINEERING

¡



»

DEV

.001

OUT

4.3

RUN

»

DEV

.001

OUT

4.3

RUN

CONFIGURATION 3

™£¢

CONTROLLERS

LOOP DECOUPLE

AIR MISER

LOAD SHARE

¡


CONFIGURATION 4

™£

RECYCLE BALANCE

SIDE STREAM

VS & CR

¡



»

DEV

.001

OUT

4.3

RUN

»

DEV

.001

OUT

4.3

RUN

¢ FALLBACK

CONFIGURATION 5

™£¢

POC

SPAN AND OFFSET

TEST

ALARM FT

¡


CONFIGURATION 6

™

OIM NAMES

VAR LIST

¡



»

DEV

.001

OUT

4.3

RUN

»

DEV

.001

OUT

4.3

RUN

UNITS

¢ LIMIT CONTROL

April 20, 1998


5-15

Figure 5-11 Sample Antisurge Subgroup and Parameter Lists

If there is no subgroup associated with the chosen parameter group, the OIM will go directly from the Configuration menu to a parameter list like that shown in the right panel of Figure 5-11.

Selecting a parameter from the Config Vars screen will display an entry screen for the parameter, from which its value can be viewed or changed. The appearance of the entry screen depends on the display type of the parameter. The procedures for entering and changing parameter values using each type of entry screen are presented in UM4003, Series 4 Fault Tolerant Operating System.

OIM Service The OIM Service menu option allows the user to make various adjustments to the LCD panel, perform several OIM diagnostic procedures, and set certain OIM options. These procedures are presented in UM4003, Series 4 Fault Tolerant Operating System.

¡™£

CALC MODES

SO

CHAR MODES

CONFIG SUBGRPS CONFIG VARS


»

DEV

.001

OUT

4.3

RUN

»

DEV

.001

OUT

4.3

RUN

™£¢

F1 CHARACTERIZER

F2 CHARACTERIZER

F4 CHARACTERIZER

F3 CHARACTERIZER

¡

MODE

MODE

MODE

MODE¢ CHARACTERIZERS


5-16



April 20, 1998

Monitoring Application Status

6-1

Chapter 6: Monitoring Application Status

The Antisurge Controller AFM monitors and records events that occur as application software is executed. These events are recorded in two places: the alarm buffer or the history buffer. The status codes contained in these buffers allow the user to monitor the activity of the system, provide a record of the controller operation, and preserve the state of the controller when an alarm occurs.

Status CodeTypes

The Antisurge Controller application status codes are grouped into two categories:

■ Events

■ Alarms

Event codes indicate the occurrence of major events within the controller, such as a change in operating state. Alarm codes indicate problems with transmitters or other failure conditions, and require user acknowledgment or action.

MonitoringStatus Codes

The Antisurge Controller status codes are recorded in the history and alarm buffers, which are accessible through an OIM, OIS, or Modbus communications. The history buffer lists all types of status codes, whereas the alarm buffer lists only alarms.

History Buffer The History Buffer parameter is an array of 20 integers containing the 20 most recent status codes, regardless of type, that have occurred in the Antisurge Controller. When a new status code is added to the history buffer, it goes into the first location. All other codes are then moved back one place. The oldest code, which was in the last location, is then discarded.

Only one occurrence of any given alarm is entered into the history buffer regardless of the number of times the alarm occurs. That is, if a given alarm code is present in the history buffer, and the same alarm reoccurs, the alarm code will not be entered into the history buffer again.


6-2 Monitoring Application Status

The history buffer is cleared using the History Reset parameter; or from an OIM, by pressing RESET when the history buffer is displayed (see History on page 5-12).

Alarm Buffer The Alarm Buffer parameter is an array of 20 integers containing the 20 most recent alarms that have occurred in the Antisurge Controller. An alarm is a failure that requires user acknowledgment or action.

When a new alarm is received, the alarm relay is enabled causing the Alarm parameter to be set to On and the Alarm LED on the OIM to flash.

An alarm will not be removed from the buffer until it has been acknowledged and corrected. New alarms are acknowledged by asserting the Alarm Reset parameter or by pressing the RESET key on the OIM. This will also reset the alarm relay and the Alarm parameter and clear any uncorrected alarms from the alarm buffer. The Alarm LED will remain illuminated, but not flash, when the alarm buffer contains acknowledged alarms which have not yet been corrected.

Table 6-1 gives a list of the Antisurge Controller event status codes. Table 6-2 on page 6-3 gives a list of the Antisurge Controller alarm status codes.

The FT Alarm Level parameter is used to assign a criticality level to the error conditions. The FT Alarm Reset parameter is used to monitor the status of fault tolerant AFM switchover attempts.

Table 6-1 Antisurge Controller Event Codes

Event Code

Event Name Description

200 Safety On Safety On

201 Recycle Trip Recycle Trip

202 dSs Recycle Trip dSs Recycle Trip

203 Emergency Antisurge Emergency Antisurge

204 Manual Fallback Manual Fallback

205 Suspend Run Suspend Run

206 Default Output Going to Manual using default output

207 Filtered Output Going to Manual using filtered output

300 State Change Major State Change

April 20, 1998

Monitoring Application Status 6-3

Table 6-2 Antisurge Controller Alarm Codes

Alarm Code

Alarm Name Description

A00 dPo Fail Flow Transmitter Failure

A01 dPo1 Fail Flow Transmitter 1 Failure

A02 dPo2 Fail Flow Transmitter 2 Failure

A03 Ps Fail Suction Pressure Failure

A04 Pd Fail Discharge Pressure Failure

A05 dPc Fail Differential Pressure Failure

A06 dPo Side Fail Suction Pressure + or - Failure

A07 Pvi Fail Valve Inlet Pressure Failure

A08 Pd Limit SP Fail Pd Limit Set Point Failure

A09 Ps Limit SP Fail Ps Limit Set Point Failure

A0A Ts Fail Suction Temperature Failure

A0B Td Fail Discharge Temperature Failure

A0C dTc Fail Differential Temperature Failure

A0D Tac Fail Temperature After Cooler Failure

A0E N Fail Speed Failure

A0F Alpha Fail Alpha Failure

A10 kW Fail kW Failure

A11 Valve Out Fail Analog Output Failure for Valve Output

A12 Remote Low Clamp Fail Remote Low Output Clamp Set Point Failure

A13 Control Override Fail Failure of Control Override Analog Input

A14 SO Initial Fail Safety On Initial Value Failure

A15 dPo Channel Fail dPo Channel Failure

A16 P Channel Fail P Channel Failure

A17 T Channel Fail T Channel Failure

A18 Pis Fail Interstage Pressure Failure

A19 Tis Fail Interstage Temperature Failure

A1A Ps1 Fail Suction Pressure 1 Failure

A1B Ps2 Fail Suction Pressure 2 Failure

A1C Pd1 Fail Discharge Pressure 1 Failure

A1D Pd2 Fail Discharge Pressure 2 Failure

A1E Ts1 Fail Suction Temperature 1 Failure

A1F Ts2 Fail Suction Temperature 2 Failure

A20 Td1 Fail Discharge Temperature 1 Failure

A21 Td2 Fail Discharge Temperature 2 Failure

A22 dPo Side1 Fail Side Stream Flow 1 Failure

A23 dPo Side2 Fail Side Stream Flow 2 Failure

B00 dPo Max Diff Fail Max Differential Between Selected dPos Failure


6-4 Monitoring Application Status

B01 S Out Fail Analog Output Failure for S Output

B02 b Out Fail Analog Output Failure for b Output

B03 Rc Out Fail Analog Output Failure for Rc Output

B04 Dev Out Fail Analog Output Failure for Dev Output

B05 Minimum Flow Mode

Running in Minimum Flow Mode

B06 Tac Fallback Substitute Td for Tac Fallback

B07 Default Sigma Fallback

Substitute Default Sigma for Sigma Fallback

B08 Temperature Based Hp

Using Temperature-Based Equation to Calculate Hp

B09 Default Rc Fallback

Substitute Default Rc for Rc Fallback

B0A Default N Fallback Substitute Default Speed for N Fallback

B0B Default Alpha Fallback

Substitute Default Alpha for Alpha Fallback

B0C Adj Flow Rate Fallback

Substitute Default Adjacent Flow Rate for Adjacent Compressor

B0D Pvi Fallback Remove Valve Inlet Compensation

B0E Position Fail Position ANI Failure

B0F Position Deviation Position Deviation Failure

B10 Default Ps Fallback

Substitute Default Ps for Ps Fallback

B11 Control Ovrd Disabled

Control Override Disabled

B12 Ss Out Fail Analog Output Failure for Ss Output

Alarm Code

Alarm Name Description

April 20, 1998

Parameter Cross-References A-1

Appendix A: Parameter Cross-References

Table A-1, below, gives a cross-reference between the Parameter Name and Symbol for each Antisurge Controller application parameter. The Parameter Names are listed in alphabetical order, as they appear in Table 4-1 on page 4-4.

Table A-2 on page A-9 lists the Parameter Names by group and subgroup.

Table A-1 Parameter Cross-Reference

Parameter Name Symbol

ALARM as_ALARM

ALARM BUFFER as_alarm_buffer[AS_ALARM_BUF_SIZE]

ALARM RESET as_RESET

ALPHA as_alpha

ALPHA OFFSET as_alpha_offset

ALPHA SPAN as_alpha_span

ALTERNATE K as_alternate_K

ALTERNATE K ENABLE as_alternate_K_enable

ANALOG INPUTS as_ani_LTOP[AS_ANI_LTOPS][2]

ANALOG OUTPUTS as_ano_LTOP[AS_ANO_LTOPS][2]

ANTICHOKE ENABLE as_anti_choke_enable

ANTISURGE STATUS as_antisurge_status[10]

ANTISURGE STATUS LTOP as_antisurge_status_LTOP[10]

APP NAME as_oim_name[17]

APP SHORT NAME as_oim_shname[6]

B as_b

BETA 3 as_Beta_3

BETA 5 as_Beta_5

CONFIG SHOW GROUP as_config_show_group[25]

CONTROL OVERRIDE as_control_override

CONTROL OVERRIDE SCREEN as_control_override_screen

CONTROL OVERRIDE SP as_control_override_SP

CONTROLLER STATUS as_controller_status

CONTROLLER TYPE as_controller_type

CURRENT DCV as_current_dCV

CV as_CV

CV TOTAL as_CV_total

DCV as_dCV

DECOUPLE CV LTOP as_decouple_CV_LTOP[10]

DEFAULT ADJACENT FLOW ENABLE as_default_adj_dPo_enable

DEFAULT ADJACENT FLOW RATE as_default_adjacent_dPo

DEFAULT ALPHA as_default_alpha

DEFAULT ALPHA ENABLE as_default_alpha_enable

DEFAULT OUTPUT as_default_out

DEFAULT PS as_default_Ps


A-2 Parameter Cross-References

DEFAULT PS ENABLE as_default_Ps_enable

DEFAULT RC as_default_Rc

DEFAULT RC ENABLE as_default_Rc_enable

DEFAULT SIGMA as_default_sigma

DEFAULT SIGMA ENABLE as_default_sigma_enable

DEFAULT SPEED as_default_N

DEFAULT SPEED ENABLE as_default_N_enable

DENOMINATOR as_denominator

DENOMINATOR MODE as_denominator_mode

DERIVATIVE RESPONSE DB as_deriv_resp_db

DERIVATIVE RESPONSE ENABLE as_deriv_resp_enable

DERIVATIVE RESPONSE MAX as_deriv_resp_max

DERIVATIVE RESPONSE RATE as_deriv_resp_rate

DERIVATIVE RESPONSE TC as_deriv_resp_Tc

DEV THRESHOLD as_dev_threshold

DEVIATION as_dev

DIGITAL INPUTS as_dgi_LTOP8[AS_DGI8_LTOPS][8]


DIGITAL OUTPUTS as_dgo_LTOP2[AS_DGO2_LTOPS][2]

DISPLAY OUTPUT as_display_out

DOWN as_DOWN

DPC as_dPc

DPC OFFSET as_dPc_offset

DPC SPAN as_dPc_span

DPO CALC as_dPo_calc

DPO COMP as_dPo_comp

DPO DEV as_dPo_differential_alarm

DPO DIFFERENTIAL THRESHOLD as_dPo_differential_threshold

DPO RATE as_dPo_rate

DPO SAMPLES as_dPo_samples

DPO SELECT as_dPo_selected

DPO SIDE as_dPo_side

DPO SIDE OFFSET as_dPo_side_offset

DPO SIDE SPAN as_dPo_side_span

DPO USED as_dPo_used

DPO1 as_dPo1

DPO1 OFFSET as_dPo1_offset

DPO1 SPAN as_dPo1_span

DPO2 as_dPo2



DPOS MODE as_dPos_mode

DPRESSURE EU as_dpressure_eu

DPRESSURE RATE EU as_dpressure_rate_eu

DPRESSURE2 EU as_dpressure2_eu

dSs as_dSs

dSs MAX as_dSs_max

DTC as_dTc

DTC OFFSET as_dTc_offset


April 20, 1998


DTC SPAN as_dTc_span

EAS as_EAS

EAS MODE as_EAS_mode

ESD as_ESD

ESD STATUS as_esd_status

EXC SURGE as_excessive_surge

F1 CHARACTERIZER as_f1_char[10][2]

F1 CHARACTERIZER MODE as_f1_mode









FALLBACK as_FALLBACK

FILTERED POC VALID as_filtered_POC_valid

FLOW as_flow

FLOW CHANNEL as_dPo_channel

FLOW COEFFICIENT as_flow_coefficient

FLOW EU as_flow_eu

FLOW OFFSET as_flow_offset

FLOW SIDESTREAM COEFFICIENT 1 as_dPo_side_coef_1



FLOW SPAN as_flow_span

FLOW->PRESSURE TIME LAG as_dPo_Pd_time_lag

FT ALARM LEVEL as_FT_alarm_level[50]

FT ALARM RESET as_FT_alarm_reset

GEAR RATIO as_gear_ratio

HIGH CLAMP as_out_at_high_clamp

HISTORY BUFFER as_history_buffer[AS_HIST_BUF_SIZE]

HISTORY RESET as_history_reset

HP as_Hp

I OFFSET as_I_offset

IDLE SPEED SP as_N_idle_SP

K as_K

K PRIME as_K_prime

KI ADJUST as_Ki_adjust

KW as_kW

KW OFFSET as_kW_offset

KW SPAN as_kW_span

LD COMPANIONS as_decouple_companion[10]

LD COMPANIONS COEFFICIENT as_decouple_coefficient[10]

LD STATUS as_LD_status[10]

LD STATUS LTOP as_LD_status_LTOP[10]

LD VALID as_LD_valid

LIMIT as_LIMIT




LOAD SHARE GAIN as_load_share_gain

LOW CLAMP as_out_at_low_clamp

LS STATUS as_LS_status

LS STATUS LTOP as_LS_status_LTOP

MANUAL AUTO as_MANUAL_AUTO

MANUAL FALLBACK ENABLE as_manual_fallback_enable

MANUAL OVERRIDE as_manual_override

MANUAL RATE CLOSE as_manual_rate_close

MANUAL RATE OPEN as_manual_rate_open

MANUAL TARGET as_manual_target

MASTER as_master

MASTER B ENABLE as_master_b_enable

MASTER B LTOP as_master_b_LTOP

MASTER CV LTOP as_master_CV_LTOP

MASTER STATUS as_master_status

MASTER STATUS LTOP as_master_status_LTOP

MAX +DPD as_Pd_max_deriv_pos

MAX +DPO as_dPo_max_deriv_pos

MAX -DPD as_Pd_max_deriv_neg

MAX -DPO as_dPo_max_deriv_neg

MINIMUM FLOW as_dPo_min

MINIMUM FLOW CONTROL ENABLE as_min_flow_control_enable

MINIMUM FLOW SETPOINT as_min_dPo_level

MINIMUM PRESSURE as_Pd_min

MINIMUM SPEED as_N_min

N as_N

N OFFSET as_N_offset

N SPAN as_N_span

NET FLOW AVAILABLE as_net_flow_available

NOT RUNNING as_not_running

NUMERATOR as_numerator

NUMERATOR MODE as_numerator_mode

OUTPUT as_out

OUTPUT HIGH LIMIT as_out_high_limit

OUTPUT LOW LIMIT as_out_low_limit

OUTPUT REVERSE as_out_reverse

OUTPUT TRACKING RATE as_control_override_rate

P OFFSET as_P_offset

PD as_Pd

PD DGO SWITCH LEVEL as_Pd_switch_SP

PD LIMIT ENABLE as_Pd_limit_enable

PD LIMIT SP as_Pd_limit_SP

PD LIMIT SP DEFAULT as_Pd_limit_SP_default

PD LIMIT STATUS as_Pd_limit_status

PD OFFSET as_Pd_offset

PD PID DZ as_Pd_PID_db

PD PID KD as_Pd_PID_Kd

PD PID KI as_Pd_PID_Ki

PD PID KP as_Pd_PID_Kp


April 20, 1998


PD PID TF as_Pd_PID_Tf

PD RATE as_Pd_rate

PD SAMPLES as_Pd_samples

PD SPAN as_Pd_span

PID VELOCITY HIGH LIMIT as_PID_vel_high_limit

PID VELOCITY LOW LIMIT as_PID_vel_low_limit

PIS as_Pis

PIS OFFSET as_Pis_offset

PIS SPAN as_Pis_span

POC as_POC

POC CV as_POC_CV

POC CV LTOP as_POC_CV_LTOP

POC DCV as_POC_dcv

POC ENABLE as_POC_enable

POC FILTERED DELTA as_POC_Pd_delta

POC FILTERED DELTA MAX as_POC_Pd_delta_max

POC FILTERED GAIN as_POC_Pd_filter_gain

POC FILTERED THRESHOLD as_POC_Pd_filter_db

POC PV TF as_POC_Pd_filter_Tf

POC STATUS as_POC_status

POS as_pos

POS DELTA DELAY as_pos_delta_delay

POS DELTA MAX as_pos_delta_max

POS FEEDBACK REVERSE as_pos_feedback_reverse

POWER EU as_power_eu

PRESSURE CHANNEL as_P_channel

PRESSURE EU as_pressure_eu

PRESSURE RATE EU as_pressure_rate_eu

PRESSURE->FLOW TIME LAG as_Pd_dPo_time_lag

PRESSURE2 EU as_pressure2_eu

PS as_Ps

PS DGO SWITCH LEVEL as_Ps_switch_SP

PS LIMIT ENABLE as_Ps_limit_enable

PS LIMIT PV as_Ps_limit_PV

PS LIMIT SP as_Ps_limit_SP

PS LIMIT SP DEFAULT as_Ps_limit_SP_default

PS LIMIT STATUS as_Ps_limit_status

PS OFFSET as_Ps_offset

PS PID DZ as_Ps_PID_db

PS PID KD as_Ps_PID_Kd

PS PID KI as_Ps_PID_Ki

PS PID KP as_Ps_PID_Kp

PS PID TF as_Ps_PID_Tf

PS SPAN as_Ps_span

PURGE as_PURGE

PURGE ENABLE as_purge_enable

PURGE RATE as_purge_rate

PVI as_Pvi

PVI OFFSET as_Pvi_offset




PVI SPAN as_Pvi_span

Q MAX as_Q_max

Q MAX CHARACTERIZER as_Q_max_char[10][2]

Q MAX COEFFICIENT as_Q_max_coefficient

Q REC OUT CHARACTERIZER as_Q_rec_out_char[10][2]

Q REC RC CHARACTERIZER as_Q_rec_Rc_char[10][2]

Q RECYCLE as_Q_rec

Q USER as_Q_user

Q USER COEFFICIENT as_Q_user_coefficient

R as_R

RB COMPANIONS as_rec_balance_companion[10]

RB CV LTOP as_RB_CV_LTOP[10]

RB RATE as_rec_balance_rate

RB VALID as_RB_valid

RB VALID LTOP as_RB_valid_LTOP[10]

RC as_Rc

RC LIMIT ENABLE as_Rc_limit_enable

RC LIMIT SP as_Rc_limit_SP

RC LIMIT SP DEFAULT as_Rc_limit_SP_default

RC LIMIT STATUS as_Rc_limit_status

RC PID DZ as_Rc_PID_db

RC PID KD as_Rc_PID_Kd

RC PID KI as_Rc_PID_Ki

RC PID KP as_Rc_PID_Kp

RC PID TF as_Rc_PID_Tf

RC SPAN as_Rc_span

RECYCLE TRIP TEST as_RT_test

REMOTE LOW CLAMPING as_remote_low_clamping

RT as_RT

RT COUNT as_RT_count

RT DEADTIME as_RT_deadtime

RT DERIVATIVE RESPONSE ENABLE as_RT_deriv_enable

RT DISTANCE as_RT_distance

RT dSs DELAY as_RT_dSs_delay

RT dSs LEVEL as_RT_dSs_level

RT dSs RESPONSE as_RT_dSs_response

RT KD as_RT_Kd

RT KP as_RT_Kp

RT MAX AMPLITUDE as_RT_max

RT STATUS as_RT_status

RUNNING as_running

S as_S

S CALC UPDATED as_S_calc_updated

S CONTROL START LEVEL as_S_control_start_level

S CONTROL START SPEED as_S_control_N_start

S CONTROL STOP SPEED as_S_control_N_stop

S CONTROLLER COMPANIONS as_S_control_companion[10]

S FAILURE as_S_failure

S TF as_S_Tf


April 20, 1998


SELECTED I as_selected_I

SELECTED P as_selected_P

SERIES as_series

SHUTDOWN MANUAL ENABLE as_shutdown_manual_enable

SIDE STREAM COMP MODE as_sidestream_comp_mode

SIDE STREAM COMPANION as_sidestream_companion

SIGMA as_sigma

SIGMA TF as_sigma_Tf

SO as_SO

SO B4 as_SO_b4

SO B4 RATE as_SO_b4_rate

SO BIAS as_SO_bias

SO DEADTIME as_SO_deadtime

SO DISTANCE as_SO_distance

SO INITIAL as_SO_initial

SO TIME BASED ENABLE as_SO_time_based_enable

Ss as_Ss

Ss SAMPLES as_Ss_samples

START RATE as_start_rate

STARTUP TIME as_start_time

STATE as_state

STATUS as_status

STOP as_STOP

STOP ENABLE as_stop_enable

STOP RATE as_stop_rate

STOP STATUS as_stop_status

STOP TIME as_stop_time

SUCTION PRESSURE EU as_suction_pressure_eu

SUCTION PRESSURE2 EU as_suction_pressure2_eu

SURGE COUNT as_surge_count

SURGE COUNT RESET as_surge_count_reset

SURGE COUNT SHUTDOWN RESET as_shutdown_srgcnt_reset

SURGE DZ as_PID_db

SURGE KI as_PID_Ki

SURGE KP as_PID_Kp

SURGE RELAY THRESHOLD as_surge_relay_threshold

SURGES as_surge_count_total

T AIR as_Tair

T AIR GAIN as_Tair_gain

T AIR NORMAL as_Tair_normal

T CW as_Tcw

T CW GAIN as_Tcw_gain

T CW NORMAL as_Tcw_normal

T RATIO as_temp_ratio

TAC as_Tac

TAC OFFSET as_Tac_offset

TAC SPAN as_Tac_span

TD as_Td

TD DGO SWITCH LEVEL as_Td_switch_SP




TD OFFSET as_Td_offset

TD SPAN as_Td_span

TEMPERATURE BASED HP ENABLE as_temp_based_Hp_enable

TEMPERATURE CHANNEL as_T_channel

TEMPERATURE EU as_temperature_eu

TEMPERATURE2 EU as_temperature2_eu

TIGHT SHUT OFF DISTANCE as_tight_off_distance

TIS as_Tis

TIS OFFSET as_Tis_offset

TIS SPAN as_Tis_span

TRACK as_TRACK

TS as_Ts

TS OFFSET as_Ts_offset

TS SPAN as_Ts_span

UP as_UP

USER as_user

USER OFFSET as_user_offset

USER SPAN as_user_span

VALVE CHARACTERIZER as_valve_char[10][2]

VALVE DEADBAND BIAS as_out_db_bias

VALVE DEADBAND BIAS THRESHOLD as_out_db_bias_threshold

VALVE MODE as_valve_mode

VALVE SHARING COMPANIONS as_valve_share_companion[10]

VALVE SHARING MODE as_valve_share_mode

VARIABLE LIST as_var_list[63]

VS as_VS

VS CV LTOP as_valve_share_CV_LTOP[10]

VS I LTOP as_valve_share_I_LTOP[10]

VS P LTOP as_valve_share_P_LTOP[10]

VS RT as_VS_RT

VS S LTOP as_valve_share_S_LTOP[10]

VS STATUS as_VS_status


April 20, 1998


Table A-2 Parameters Listed by Group and Subgroup

Group Subgroup Parameter Name Symbol

AIR MISER AM LS STATUS LTOP as_LS_status_LTOP

NET FLOW AVAILABLE as_net_flow_available

Q MAX CHARACTERIZER as_Q_max_char[10][2]

Q MAX COEFFICIENT as_Q_max_coefficient

Q REC OUT CHARACTERIZER as_Q_rec_out_char[10][2]

Q REC RC CHARACTERIZER as_Q_rec_Rc_char[10][2]

Q USER COEFFICIENT as_Q_user_coefficient

T AIR GAIN as_Tair_gain

T AIR NORMAL as_Tair_normal

T CW GAIN as_Tcw_gain

T CW NORMAL as_Tcw_normal

ALARM ALARM ALARM BUFFER as_alarm_buffer[AS_ALARM_BUF_SIZE]

ALARM RESET as_RESET

HISTORY HISTORY BUFFER as_history_buffer[AS_HIST_BUF_SIZE]

HISTORY RESET as_history_reset

ALARM FT ALARM FT ALARM LEVEL as_FT_alarm_level[50]

FT ALARM RESET as_FT_alarm_reset

AUTO SEQUENCE S CONTROL S CONTROL START LEVEL as_S_control_start_level

S CONTROL START SPEED as_S_control_N_start

S CONTROL STOP SPEED as_S_control_N_stop

START DEV THRESHOLD as_dev_threshold

IDLE SPEED SP as_N_idle_SP

MINIMUM FLOW as_dPo_min

MINIMUM PRESSURE as_Pd_min

MINIMUM SPEED as_N_min

START RATE as_start_rate

STARTUP TIME as_start_time

STOP PURGE ENABLE as_purge_enable

PURGE RATE as_purge_rate

STOP ENABLE as_stop_enable

STOP RATE as_stop_rate

STOP TIME as_stop_time

CALCULATE SCL ANTICHOKE ANTICHOKE ENABLE as_anti_choke_enable

CALC MODES DENOMINATOR MODE as_denominator_mode

DPOS MODE as_dPos_mode

NUMERATOR MODE as_numerator_mode

CHAR MODES F1 CHARACTERIZER MODE as_f1_mode




CHARACTERIZERS F1 CHARACTERIZER as_f1_char[10][2]






SO K as_K



CONFIG DISPLAY CONFIG SHOW GROUP as_config_show_group[25]

CONFIGURE IO ANALOG IN CONTROL OVERRIDE SCREEN as_control_override_screen

DPO DIFFERENTIAL THRESHOLD as_dPo_differential_threshold

GEAR RATIO as_gear_ratio

ANALOG OUT OUTPUT TRACKING RATE as_control_override_rate

CONTROL VALVE OUTPUT HIGH LIMIT as_out_high_limit

OUTPUT LOW LIMIT as_out_low_limit

OUTPUT REVERSE as_out_reverse

POS DELTA DELAY as_pos_delta_delay

POS DELTA MAX as_pos_delta_max

POS FEEDBACK REVERSE as_pos_feedback_reverse

TIGHT SHUT OFF DISTANCE as_tight_off_distance

VALVE CHARACTERIZER as_valve_char[10][2]

VALVE DEADBAND BIAS as_out_db_bias

VALVE DEADBAND BIAS THRESHOLD as_out_db_bias_threshold

VALVE MODE as_valve_mode

DIGITAL OUT PD DGO SWITCH LEVEL as_Pd_switch_SP

PS DGO SWITCH LEVEL as_Ps_switch_SP

TD DGO SWITCH LEVEL as_Td_switch_SP

FLOW BETA 5 as_Beta_5

FLOW CHANNEL as_dPo_channel

FLOW COEFFICIENT as_flow_coefficient

PRESSURE CHANNEL as_P_channel

TEMPERATURE CHANNEL as_T_channel

LTOP ANALOG INPUTS as_ani_LTOP[AS_ANI_LTOPS][2]

ANALOG OUTPUTS as_ano_LTOP[AS_ANO_LTOPS][2]



DIGITAL OUTPUTS as_dgo_LTOP2[AS_DGO2_LTOPS][2]

CONTROL DERIV RESPONSE DERIVATIVE RESPONSE DB as_deriv_resp_db

DERIVATIVE RESPONSE ENABLE as_deriv_resp_enable

DERIVATIVE RESPONSE MAX as_deriv_resp_max

DERIVATIVE RESPONSE RATE as_deriv_resp_rate

DERIVATIVE RESPONSE TC as_deriv_resp_Tc

FILTERS S TF as_S_Tf

SIGMA TF as_sigma_Tf

Ss SAMPLES as_Ss_samples

MANUAL MANUAL OVERRIDE as_manual_override

MANUAL RATE CLOSE as_manual_rate_close

MANUAL RATE OPEN as_manual_rate_open

SHUTDOWN MANUAL ENABLE as_shutdown_manual_enable

PID KI ADJUST as_Ki_adjust

PID VELOCITY HIGH LIMIT as_PID_vel_high_limit

PID VELOCITY LOW LIMIT as_PID_vel_low_limit

SURGE DZ as_PID_db

SURGE KI as_PID_Ki

SURGE KP as_PID_Kp

CONTROLLERS MASTER MASTER as_master


April 20, 1998


ENGINEERING ENGINEERING DPRESSURE EU as_dpressure_eu

UNITS UNITS DPRESSURE RATE EU as_dpressure_rate_eu

DPRESSURE2 EU as_dpressure2_eu

FLOW EU as_flow_eu

POWER EU as_power_eu

PRESSURE EU as_pressure_eu

PRESSURE RATE EU as_pressure_rate_eu

PRESSURE2 EU as_pressure2_eu

SUCTION PRESSURE EU as_suction_pressure_eu

SUCTION PRESSURE2 EU as_suction_pressure2_eu

TEMPERATURE EU as_temperature_eu

TEMPERATURE2 EU as_temperature2_eu

FALLBACK ENABLE ALTERNATE K ENABLE as_alternate_K_enable

DEFAULT ADJACENT FLOW ENABLE as_default_adj_dPo_enable

DEFAULT ALPHA ENABLE as_default_alpha_enable

DEFAULT PS ENABLE as_default_Ps_enable

DEFAULT RC ENABLE as_default_Rc_enable

DEFAULT SIGMA ENABLE as_default_sigma_enable

DEFAULT SPEED ENABLE as_default_N_enable

MANUAL FALLBACK ENABLE as_manual_fallback_enable

MINIMUM FLOW CONTROL ENABLE as_min_flow_control_enable

TEMPERATURE BASED HP ENABLE as_temp_based_Hp_enable

VALUE ALTERNATE K as_alternate_K

DEFAULT ADJACENT FLOW RATE as_default_adjacent_dPo

DEFAULT ALPHA as_default_alpha

DEFAULT OUTPUT as_default_out

DEFAULT PS as_default_Ps

DEFAULT RC as_default_Rc

DEFAULT SIGMA as_default_sigma

DEFAULT SPEED as_default_N

MINIMUM FLOW SETPOINT as_min_dPo_level

INOUT ALPHA as_alpha

DPC as_dPc

DPO CALC as_dPo_calc

DPO COMP as_dPo_comp

DPO DEV as_dPo_differential_alarm

DPO SELECT as_dPo_selected

DPO SIDE as_dPo_side

DPO USED as_dPo_used

DPO1 as_dPo1

DPO2 as_dPo2

dSs as_dSs

dSs MAX as_dSs_max

DTC as_dTc

FLOW as_flow

HP as_Hp

KW as_kW

N as_N

PD as_Pd




INOUT PIS as_Pis

POS as_pos

PS as_Ps

PVI as_Pvi

Q MAX as_Q_max

Q RECYCLE as_Q_rec

Q USER as_Q_user

R as_R

RC as_Rc

S as_S

SIGMA as_sigma

Ss as_Ss

SURGES as_surge_count_total

T AIR as_Tair

T CW as_Tcw

T RATIO as_temp_ratio

TAC as_Tac

TD as_Td

TIS as_Tis

TS as_Ts

USER as_user

LIMIT CONTROL PD PD LIMIT ENABLE as_Pd_limit_enable

PD LIMIT SP as_Pd_limit_SP

PD LIMIT SP DEFAULT as_Pd_limit_SP_default

PD PID DZ as_Pd_PID_db

PD PID KD as_Pd_PID_Kd

PD PID KI as_Pd_PID_Ki

PD PID KP as_Pd_PID_Kp

PD PID TF as_Pd_PID_Tf

PS PID TF as_Ps_PID_Tf

RC PID TF as_Rc_PID_Tf

PS PS LIMIT ENABLE as_Ps_limit_enable

PS LIMIT PV as_Ps_limit_PV

PS LIMIT SP as_Ps_limit_SP

PS LIMIT SP DEFAULT as_Ps_limit_SP_default

PS PID DZ as_Ps_PID_db

PS PID KD as_Ps_PID_Kd

PS PID KI as_Ps_PID_Ki

PS PID KP as_Ps_PID_Kp

RC RC LIMIT ENABLE as_Rc_limit_enable

RC LIMIT SP as_Rc_limit_SP

RC LIMIT SP DEFAULT as_Rc_limit_SP_default

RC PID DZ as_Rc_PID_db

RC PID KD as_Rc_PID_Kd

RC PID KI as_Rc_PID_Ki

RC PID KP as_Rc_PID_Kp

LOAD SHARE LS BETA 3 as_Beta_3

LOAD SHARE GAIN as_load_share_gain

MASTER CV LTOP as_master_CV_LTOP


April 20, 1998


LOAD SHARE MASTER MASTER STATUS LTOP as_master_status_LTOP

LOOP DECOUPLE LD DECOUPLE CV LTOP as_decouple_CV_LTOP[10]

LD COMPANIONS as_decouple_companion[10]

LD COMPANIONS COEFFICIENT as_decouple_coefficient[10]

LD STATUS LTOP as_LD_status_LTOP[10]

OIM NAMES APP NAME as_oim_name[17]

APP SHORT NAME as_oim_shname[6]

OPERATOR ALARM as_ALARM

B as_b

CONTROL OVERRIDE as_control_override

CONTROLLER STATUS as_controller_status

CURRENT DCV as_current_dCV

DEVIATION as_dev

DISPLAY OUTPUT as_display_out

DOWN as_DOWN

EAS as_EAS

ESD as_ESD

FALLBACK as_FALLBACK

LIMIT as_LIMIT

MANUAL AUTO as_MANUAL_AUTO

MANUAL TARGET as_manual_target

POC as_POC

PURGE as_PURGE

RT as_RT

RT COUNT as_RT_count

SO as_SO

STATE as_state

STOP as_STOP

SURGE COUNT as_surge_count

SURGE COUNT RESET as_surge_count_reset

TRACK as_TRACK

UP as_UP

VS as_VS

POC POC FILTERED POC VALID as_filtered_POC_valid

POC CV as_POC_CV

POC CV LTOP as_POC_CV_LTOP

POC DCV as_POC_dcv

POC ENABLE as_POC_enable

POC FILTERED DELTA as_POC_Pd_delta

POC FILTERED DELTA MAX as_POC_Pd_delta_max

POC FILTERED GAIN as_POC_Pd_filter_gain

POC FILTERED THRESHOLD as_POC_Pd_filter_db

POC PV TF as_POC_Pd_filter_Tf

RECYCLE RB RB COMPANIONS as_rec_balance_companion[10]

BALANCE RB CV LTOP as_RB_CV_LTOP[10]

RB RATE as_rec_balance_rate

RB VALID LTOP as_RB_valid_LTOP[10]

SIDE STREAM SS FLOW SIDESTREAM COEFFICIENT 1 as_dPo_side_coef_1





SIDE STREAM SS FLOW SIDESTREAM COEFFICIENT 3 as_dPo_side_coef_3

SIDE STREAM COMP MODE as_sidestream_comp_mode

SIDE STREAM COMPANION as_sidestream_companion

SO & RT EAS DPO RATE as_dPo_rate

DPO SAMPLES as_dPo_samples

EAS MODE as_EAS_mode

FLOW->PRESSURE TIME LAG as_dPo_Pd_time_lag

MAX +DPD as_Pd_max_deriv_pos

MAX +DPO as_dPo_max_deriv_pos

MAX -DPD as_Pd_max_deriv_neg

MAX -DPO as_dPo_max_deriv_neg

PD RATE as_Pd_rate

PD SAMPLES as_Pd_samples

PRESSURE->FLOW TIME LAG as_Pd_dPo_time_lag

RT RT DEADTIME as_RT_deadtime

RT DERIVATIVE RESPONSE ENABLE as_RT_deriv_enable

RT DISTANCE as_RT_distance

RT dSs DELAY as_RT_dSs_delay

RT dSs LEVEL as_RT_dSs_level

RT dSs RESPONSE as_RT_dSs_response

RT KD as_RT_Kd

RT KP as_RT_Kp

RT MAX AMPLITUDE as_RT_max

SO MASTER B ENABLE as_master_b_enable

MASTER B LTOP as_master_b_LTOP

SO B4 as_SO_b4

SO B4 RATE as_SO_b4_rate

SO BIAS as_SO_bias

SO DEADTIME as_SO_deadtime

SO DISTANCE as_SO_distance

SO INITIAL as_SO_initial

SO TIME BASED ENABLE as_SO_time_based_enable

SURGE COUNT SHUTDOWN RESET as_shutdown_srgcnt_reset

SURGE RELAY THRESHOLD as_surge_relay_threshold

SPAN AND OFFSET ALPHA OFFSET as_alpha_offset

OFFSET DPC OFFSET as_dPc_offset

DPO SIDE OFFSET as_dPo_side_offset



DTC OFFSET as_dTc_offset

FLOW OFFSET as_flow_offset

KW OFFSET as_kW_offset

N OFFSET as_N_offset

PD OFFSET as_Pd_offset

PIS OFFSET as_Pis_offset

PS OFFSET as_Ps_offset

PVI OFFSET as_Pvi_offset

TAC OFFSET as_Tac_offset

TD OFFSET as_Td_offset


April 20, 1998


SPAN AND OFFSET TIS OFFSET as_Tis_offset

OFFSET TS OFFSET as_Ts_offset

USER OFFSET as_user_offset

SPAN ALPHA SPAN as_alpha_span

DPC SPAN as_dPc_span

DPO SIDE SPAN as_dPo_side_span



DTC SPAN as_dTc_span

FLOW SPAN as_flow_span

KW SPAN as_kW_span

N SPAN as_N_span

PD SPAN as_Pd_span

PIS SPAN as_Pis_span

PS SPAN as_Ps_span

PVI SPAN as_Pvi_span

RC SPAN as_Rc_span

TAC SPAN as_Tac_span

TD SPAN as_Td_span

TIS SPAN as_Tis_span

TS SPAN as_Ts_span

USER SPAN as_user_span

STATUS STATUS ANTISURGE STATUS as_antisurge_status[10]

CONTROL OVERRIDE SP as_control_override_SP

CONTROLLER TYPE as_controller_type

CV as_CV

CV TOTAL as_CV_total

ESD STATUS as_esd_status

EXC SURGE as_excessive_surge

HIGH CLAMP as_out_at_high_clamp

LD STATUS as_LD_status[10]

LD VALID as_LD_valid

LOW CLAMP as_out_at_low_clamp

LS STATUS as_LS_status

MASTER STATUS as_master_status

NOT RUNNING as_not_running

OUTPUT as_out

PD LIMIT STATUS as_Pd_limit_status

POC STATUS as_POC_status

PS LIMIT STATUS as_Ps_limit_status

RB VALID as_RB_valid

RC LIMIT STATUS as_Rc_limit_status

REMOTE LOW CLAMPING as_remote_low_clamping

RT STATUS as_RT_status

RUNNING as_running

S CALC UPDATED as_S_calc_updated

S FAILURE as_S_failure

STATUS as_status

STOP STATUS as_stop_status




STATUS STATUS VS RT as_VS_RT

VS STATUS as_VS_status

TEST DCV DCV as_dCV

PID DENOMINATOR as_denominator

K PRIME as_K_prime

TEST NUMERATOR as_numerator

RECYCLE TRIP TEST as_RT_test

SELECTED I as_selected_I

SELECTED P as_selected_P

VAR LIST VARIABLE LIST as_var_list[63]

VS & CR CR I OFFSET as_I_offset

P OFFSET as_P_offset

S CONTROLLER COMPANIONS as_S_control_companion[10]

VS ANTISURGE STATUS LTOP as_antisurge_status_LTOP[10]

SERIES as_series

VALVE SHARING COMPANIONS as_valve_share_companion[10]

VALVE SHARING MODE as_valve_share_mode

VS CV LTOP as_valve_share_CV_LTOP[10]

VS I LTOP as_valve_share_I_LTOP[10]

VS P LTOP as_valve_share_P_LTOP[10]

VS S LTOP as_valve_share_S_LTOP[10]


April 20, 1998

Index–1

AAccess Levels, Parameters 4-3Adjacent Flow Fallback 3-27Aftercooler Temperature Failure 3-31Air Miser 3-78

Maximum Flow 3-79Recycle Flow 3-79User Flow 3-79

Alarm Buffer 6-2OIM Display 5-11

Alarm LED, OIM 5-6, 6-2Alarm Status Codes 6-3Antichoke Control 3-81

Control Lines 3-82Redundant Signal Selection 3-83Safety Margin 3-82Ss Variable 3-83

Antisurge Control Overview 2-1Antisurge PI Response 3-40Application Selection, OIM 5-12Auto LED, OIM 5-7Automatic Sequencing 3-91

CCalculated Process Variables 3-20

Compression Ratio 3-20Mass Flow Rate 3-22Multi-Section Compressor Flow Rates 3-24Polytropic Head Exponent 3-21Reduced Polytropic Head 3-21Reported Flow 3-22Suction Flow 3-21Temperature Ratio 3-20

CharacterizersControl Line 3-9Surge Limit 3-4

Cold Recycle (S) Control 3-69Run Freeze Fallback 3-71S Variable 3-70Safety Margin 3-70

Companion ControllersLoop Decoupling 3-63Recycle Balancing 3-68S Control 3-69Side Stream 3-22, 3-25Valve Sharing 3-57

Compression Ratio 3-20Compression Ratio Fallback 3-28Compression Ratio Limiting Control 3-55

Compressor MapControl Lines 3-8Multi-Dimensional Coordinate Systems 3-2Operating Point 2-4, 3-1, 3-2Performance Curve 2-4Resistance Curve 2-4Two-Dimensional Coordinate Systems 3-2

Compressor Run Status 3-92Configuration, OIM 5-13Control Element Compensation 3-72Control Keys, OIM 5-5Control Lines 3-8

Antichoke Control 3-82Characterizers 3-9Recycle Trip Line (RTL) 3-8, 3-9, 3-11Safety On Line (SOL) 3-8, 3-9, 3-11Surge Control Line (SCL) 2-6, 3-8, 3-9, 3-10Surge Limit Line (SLL) 2-5, 3-1, 3-8, 3-9,

3-10Tight Shut-Off Line (TSL) 3-8, 3-9, 3-11

Control Override 3-77Control Responses

Antichoke Control 3-82Antisurge PI 3-40Derivative 3-41Filtered POC 3-62Limiting 3-52

Compression Ratio 3-55Discharge Pressure 3-54Suction Pressure 3-53

Load Balancing 3-67Loop Decoupling 3-63POC 3-60Recycle Balancing 3-67Recycle Trip 3-42Recycle Trip Test 3-47Recycle Trip, Derivative 3-44Recycle Trip, dSs 3-45Safety On 3-47Safety On, Accumulated 3-49

Controller Status 5-2Controllers

Cold Recycle (S) 3-69Load Sharing 3-64, 3-67Master 3-60, 3-64, 3-65, 3-67

Coordinate SystemsMulti-Dimensional 3-2Two-Dimensional 3-2


Index–2

DdCV Signal Selection 3-34Dead Zone, PID Algorithm 3-39Denominator Mode (Ss) 3-3, 3-5Denominator Modes, Valid 3-5Derivative Response 3-41Derivative Response, Recycle Trip 3-44Deviation, Operating Point 3-12, 3-76, 5-1

Recycle Trip 3-42Discharge Pressure Failure 3-31Discharge Pressure Limiting Control 3-54Discharge Temperature Failure 3-32Display Units 3-18Down Input, Manual Operation 3-89dPo Failure 3-32dPos Modes 3-7dSs Response, Recycle Trip 3-45

EEAS Modes 3-51EAS Surge Detection 3-50Emergency Antisurge (EAS) Algorithm 3-50Engineering Units 3-18Event Status Codes 6-2

FFallback LED, OIM 3-27, 5-7Fallback Strategies 3-27

Adjacent Flow Fallback 3-27Aftercooler Temperature Failure 3-31Compression Ratio Fallback 3-28Discharge Pressure Failure 3-31Discharge Temperature Failure 3-32dPo Failure 3-32Guide Vane Angle Failure 3-33Inlet Valve Fallback 3-28Limiting Control Fallback 3-28Minimum Flow Fallback 3-28Polytropic Head Fallback 3-29Run Freeze Fallback 3-30Sigma (Hp Exponent) Fallback 3-30Speed Failure 3-32Suction Pressure Failure 3-32Suction Temperature Failure 3-32Valve Sharing Fallback 3-30

Fault Detection, Inputs and Outputs 3-14Fault LED, OIM 5-7Filtered POC Response 3-62Functional Diagram 3-35

GGuide Vane Angle Failure 3-33

HHistory Buffer 6-1

OIM Display 5-12

IIdle State 3-87Inlet Valve Fallback 3-28Input Failures

Aftercooler Temperature 3-31Discharge Pressure 3-31Discharge Temperature 3-32dPo 3-32Guide Vane Angle 3-33Speed 3-32Suction Pressure 3-32Suction Temperature 3-32

Inputs and OutputsConfiguration 3-13Fault Detection 3-14LTOP Arrays 3-14Packet Data 3-15

Integral Response, SlowingAfter Limiting Control 3-53After POC 3-61After Recycle Trip 3-46After Valve Sharing 3-59

Integrated Control Features 3-56

LLEDs, OIM 5-6

Alarm 5-6, 5-12, 6-2Auto 5-7Fallback 3-27, 5-7Fault 5-7Limit 3-52, 3-60, 5-7Manual 5-8Recycle Trip 3-43, 3-46, 5-7Run 5-8Safety On 5-7Stop 5-8Track 5-7

Limit LED, OIM 3-52, 3-60, 5-7

April 20, 1998

Index–3

Limiting Control 3-52Compression Ratio 3-55Discharge Pressure 3-54Fallback 3-28LED, OIM 3-52, 3-60, 5-7PI Direction 3-38PI Span 3-38Screens, OIM 5-4Slowing Integral Response 3-53Status 3-52Suction Pressure 3-53

Limiting Control Fallback 3-28Limiting Control Screens, OIM 5-4Load Balancing 3-64

Parallel Compressors 3-67Series Compressors 3-67

Load Balancing Response 3-67Load Balancing Variable, R 3-23Load Sharing 3-64, 3-65Load Sharing Controller 3-64, 3-67Load Sharing Gain 3-66Load Sharing Threshold 3-66Loop Decoupling 3-63

Control Response 3-63Loop Decoupling Companion Controllers 3-63Loop Decoupling CV 3-34, 3-63Loop Decoupling Gain 3-64LTOP Arrays, Inputs and Outputs 3-14

MMain Control Screen, OIM 5-1Manual LED, OIM 5-8Manual Operation 3-89

Up/Down Inputs 3-89Manual Override 3-46, 3-90

Recycle Trip 3-46Manual State 3-89Manual Target 3-89Mass Flow Rate 3-22

Multisection Compressor 3-24Normalized 3-23

Master Controller 3-60, 3-64, 3-65, 3-67Maximum Flow, Air Miser 3-79Measured Process Variables 3-16

Menu System, OIM 5-10Alarm Buffer 5-11Application 5-12Configuration 5-13Control Keys 5-10Control Screen 5-11History Buffer 5-12OIM Service 5-15Variables 5-11

Minimum Flow Fallback 3-28Modbus Register Scaling 3-18Monitoring Status Codes 6-1Multi-Section Compressor Flow Rates 3-24

NNumerator Mode (Ss) 3-3, 3-4Numerator Modes, Valid 3-5

OOperating Mode Selection, OIM 5-9Operating Point 2-4, 3-1, 3-2, 3-12Operating States 3-84

Idle 3-87Manual 3-89Purge 3-87Remote Run 3-91Run 3-89Shutdown 3-86Starting 3-88Transitions 3-84, 3-85

Operator Interface Module (OIM) 5-1Alarm Buffer 5-11Application Selection 5-12Configuration 5-13Control Keys 5-5History Buffer 5-12LEDs 5-6

Alarm 5-6, 5-12, 6-2Auto 5-7Fallback 3-27, 5-7Fault 5-7Limit 3-52, 3-60, 5-7Manual 5-8Recycle Trip 3-43, 3-46, 5-7Run 5-8Safety On 5-7Stop 5-8Track 5-7


Index–4

Limiting Control Screens 5-4Main Control Screen 5-1Menu System 5-10

Alarm Buffer 5-11Application 5-12Configuration 5-13Control Keys 5-10Control Screen 5-11History Buffer 5-12OIM Service 5-15Variables 5-11

Operating Mode Selection 5-9Service 5-15Variables Display 5-11

Output Clamps 3-72Output Reverse 3-77Output, Controller 3-72

PPacket Data 3-15Parallel Compressors 3-67

Load Balancing 3-67Recycle Balancing 3-67

ParametersAccess Levels 4-3Binary 4-2Cross References A-1

By Group A-9By Parameter Name A-1

Descriptions 4-15Floating-Point 4-2Integer 4-2Table 4-4

Performance Curve 2-4PI Response

Antisurge 3-40Recycle Trip 3-45

PID Algorithm 3-37Dead Zone 3-39Direction 3-38Span 3-38Velocity Clamps 3-40

Polytropic Head 3-21Polytropic Head Exponent 3-21Polytropic Head Fallback 3-29Position Feedback, Recycle Valve 3-78Pressure Override Control (POC) 3-60, 3-65

Filtered POC Response 3-62Slowing Integral Response 3-61Status 3-61

Principals of Surge Prevention 2-3Process Variables 3-16

Calculated 3-20Measured 3-16Redundant Signal Selection 3-17Scaling 3-18

Proximity to Surge 3-1Proximity-to-Surge Variable (Ss) 3-1

Antichoke Control 3-83Denominator 3-3, 3-5Numerator 3-3, 3-4

Purge State 3-87

RR, Load Balancing Variable 3-23Recycle Balancing Companion Controllers 3-68Recycle Balancing Response 3-67Recycle Flow, Air Miser 3-79Recycle Trip 3-42

Derivative Response 3-44Deviation 3-42dSs Response 3-45LED, OIM 3-43, 3-46, 5-7Manual Override 3-46Maximum Step Size 3-43PI Response During 3-45Slowing Integral Response 3-46Status 3-47Step Size 3-44Test Response 3-47, 5-9Valve Sharing Controller 3-59

Recycle Trip Distance 3-9, 3-11Recycle Trip LED, OIM 3-43, 3-46, 5-7Recycle Trip Line (RTL) 3-11Recycle Valve Position Feedback 3-78Reduced Polytropic Head 3-21Redundant Signal Selection 3-17

Antichoke Control 3-83Remote Low Clamping 3-73Remote Run State 3-91Reported Flow 3-22Resistance Curve 2-4Run Freeze Fallback 3-30

Cold Recycle (S) Control 3-71Run LED, OIM 5-8Run State 3-89Run Status 3-92

April 20, 1998

Index–5

SS Control 3-69

Run Freeze Fallback 3-71S Variable 3-70Safety Margin 3-70

S Control Companion Controller 3-69S Controller 3-69S Variable 3-66, 3-70Safety Margin 2-6, 3-9, 3-10

Antichoke Control 3-82Cold Recycle (S) Control 3-70

Safety On Bias 3-48Safety On Distance 3-9, 3-11, 3-47Safety On LED, OIM 5-7Safety On Line (SOL) 3-11Safety On Response 3-47

Accumulated 3-49Scaling

Modbus Registers 3-18Process Variables 3-18

Series Compressors, Load Balancing 3-64, 3-67Service, OIM 5-15Shutdown State 3-86Side Stream Comp Modes 3-22Side Stream Companion Controllers 3-22, 3-25Sigma (Polytropic Head Exponent) 3-21Sigma Fallback 3-30Signal Noise, Reduction 3-3, 3-41Signal Selection, dCV 3-34Speed Failure 3-32Ss (Proximity-to-Surge Variable) 3-1, 3-3

Antichoke Control 3-83Starting State 3-88Status

Compressor Run Status 3-92Controller 5-2Limiting Control 3-52Pressure Override Control (POC) 3-61Recycle Trip 3-47Valve Sharing 3-59

Status CodesAlarms 6-3Events 6-2Monitoring 6-1Types 6-1

Stop LED, OIM 5-8Suction Flow 3-21Suction Pressure Failure 3-32Suction Pressure Limiting Control 3-53

Suction Temperature Failure 3-32Surge 3-1

Prevention 2-3Surge Control Line (SCL) 2-6, 3-10Surge Count 3-48

Resetting 3-49, 5-9Total 3-50

Surge Limit Characterizers 3-4Surge Limit Line (SLL) 2-5, 3-1, 3-8, 3-10

TTemperature Ratio 3-20Tight Shut-Off 3-76Tight Shut-Off Distance 3-9, 3-11Tight Shut-Off Line (TSL) 3-11Track LED, OIM 5-7

UUp Input, Manual Operation 3-89User Flow, Air Miser 3-79

VValve Characterization Modes 3-74Valve Dead Band Compensation 3-75Valve Flow Characterization 3-73Valve Position Feedback 3-78Valve Sharing 3-57

Companion Controllers 3-57Fallback 3-30Recycle Trip 3-59Slowing Integral Response 3-59Status 3-59

Valve Sharing Fallback 3-30Variables Display, OIM 5-11Velocity Clamps, PID Algorithm 3-40


Index–6

April 20, 1998

Parameter Index–1

AAlarm 4-15, 6-2Alarm Buffer 4-15, 6-2Alarm Reset 4-15, 6-2Alpha 3-17, 3-33, 4-15Alpha Offset 4-15Alpha Span 4-16Alternate K 3-30, 4-16Alternate K Enable 3-30, 4-16Analog Inputs 3-14, 3-73, 3-77, 4-16Analog Outputs 3-14, 4-17Antichoke Enable 3-81, 4-17Antisurge Status 4-18Antisurge Status LTOP 3-58, 3-70, 4-18App Name 4-18App Short Name 4-18

Bb 3-10–12, 3-41, 3-49, 3-70, 3-82, 4-18, 5-3 Beta 3 3-66, 4-18Beta 5 3-24, 4-18

CConfig Show Group 4-19Control Override 3-77, 4-19Control Override SP 3-77–78, 4-19Controller Status 3-77, 3-79, 4-20, 5-2Controller Type 3-70, 3-81, 4-20Current dCV 3-34, 4-21CV 3-15, 3-34, 3-58–59, 3-63, 4-21CV Total 3-15, 3-34, 3-36, 3-63, 3-66, 3-68–69,3-72, 3-91, 4-21

DdCV 3-34, 4-22Decouple CV LTOP 3-63, 4-22Default Adjacent Flow Enable 3-27, 4-22Default Adjacent Flow Rate 3-27, 4-22Default Alpha 3-33, 4-22Default Alpha Enable 3-33, 4-23Default Output 3-30, 4-23Default Ps 3-32, 4-23Default Ps Enable 3-32, 4-23Default Rc 3-28, 3-31, 4-23Default Rc Enable 3-28, 3-31, 4-24Default Sigma 3-21, 3-29–32, 4-24Default Sigma Enable 3-29–30, 3-32, 4-24Default Speed 3-32, 4-24Default Speed Enable 3-32, 4-24Denominator 3-4, 4-25Denominator Mode 3-3–4, 3-6, 3-26–27, 3-32,3-69, 4-25

Derivative Response DB 3-41, 4-25Derivative Response Enable 3-41, 4-26Derivative Response Max 3-42, 4-26Derivative Response Rate 3-42, 3-49, 4-26Derivative Response Tc 3-41, 4-26Dev Threshold 3-88, 4-26Deviation 3-11–12, 3-40, 3-53, 3-59, 3-61, 3-69,3-76, 3-88, 4-27, 5-1 Digital Inputs (2) 4-27Digital Inputs (8) 4-28Digital Inputs 3-14, 3-92Digital Outputs 3-14, 4-28Display Output 3-11–12, 3-19, 3-40, 3-46, 3-53,3-59, 3-61, 3-72, 3-76–77, 3-86–87, 3-90, 4-30, 5-2,5-5Down 3-89, 4-30dPc 3-16, 4-30dPc Offset 4-30dPc Span 4-31dPo Calc 3-6, 3-20–22, 3-25–26, 3-31, 4-31dPo Comp 3-15, 3-20, 3-22, 3-24–27, 4-31dPo Dev 3-17, 4-31dPo Differential Threshold 3-17, 4-31dPo Rate 3-50–51, 4-32dPo Samples 4-32dPo Select 3-17, 4-32dPo Side 3-16–17, 3-24–25, 3-27, 3-30, 4-33dPo Side Offset 4-33dPo Side Span 4-33dPo Used 3-6, 3-17, 3-20–21, 3-24–28, 4-33dPo1 3-16–17, 4-33dPo1 Offset 4-33dPo1 Span 4-33dPo2 3-16–17, 4-34dPo2 Offset 4-34dPo2 Span 4-34dPos Mode 3-6, 3-21, 3-25–28, 3-31–33, 3-69, 4-35dPressure EU and dPressure2 EU 3-18, 4-36dPressure Rate EU 3-18, 4-36dSs 4-37dSs Max 3-41, 4-37dTc 3-16–17, 4-37dTc Offset 4-37dTc Span 4-37

EEAS 3-50, 4-37EAS Mode 3-50, 4-38ESD 3-46, 3-71, 3-86–91, 4-38ESD Status 3-86, 4-38Exc Surge 3-50, 4-39


Parameter Index–2

Ff1 Characterizer 3-3, 4-39f1 Characterizer Mode 3-3, 4-40f2 Characterizer 3-3, 4-40f2 Characterizer Mode 3-3, 4-41f3 Characterizer 3-4, 4-41f3 Characterizer Mode 3-4, 4-42f4 Characterizer 3-9, 3-12, 3-42, 4-42f4 Characterizer Mode 3-9, 3-12, 3-42, 3-71, 4-43f5 Characterizer 4-43f6 Characterizer 3-4, 4-44Fallback 3-27, 4-44Filtered POC Valid 3-62, 4-44Flow 3-15, 3-22, 3-80, 4-44Flow Channel 3-22–24, 3-80, 4-45Flow Coefficient 3-22–23, 4-45Flow EU 4-46Flow Offset 3-23, 4-46Flow Sidestream Coefficient 1 3-24, 4-46Flow Sidestream Coefficient 2 3-24, 4-47Flow Sidestream Coefficient 3 3-24, 4-47Flow Span 3-23, 4-47Flow->Pressure Time Lag 3-51, 4-47FT Alarm Level 3-14, 4-48, 6-2FT Alarm Reset 4-49, 6-2

GGear Ratio 3-19, 4-49

HHigh Clamp 3-72, 3-88, 4-49History Buffer 4-50, 6-1History Reset 4-50, 6-2Hp 3-17, 3-20–21, 3-29, 3-31–33, 4-50

II Offset 3-71, 4-50Idle Speed SP 3-87, 4-51

KK 3-3, 3-30, 4-51K Prime 3-4, 4-51Ki Adjust 3-46–47, 3-53, 3-59, 3-61, 4-51kW 3-17, 4-51kW Offset 4-52kW Span 4-52

LLD Companions 3-63, 4-52LD Companions Coefficient 3-63, 4-53LD Status 4-53LD Status LTOP 3-63, 4-53LD Valid 3-15, 3-63–64, 4-53Limit 3-52, 3-88, 4-53Load Share Gain 3-66, 4-54Low Clamp 3-72, 3-88, 4-54LS Status 4-54LS Status LTOP 3-79, 4-54

MManual Auto 3-89, 4-54Manual Fallback Enable 3-30, 4-55Manual Override 3-46, 3-89–90, 4-55Manual Rate Close 3-89–90, 4-55Manual Rate Open 3-89–90, 4-56Manual Target 3-73, 3-89–90, 4-56Master 3-60, 3-65, 4-56Master b Enable 4-57Master b LTOP 4-57Master CV LTOP 3-65, 4-57Master Status 4-57Master Status LTOP 3-60, 4-57Max +dPd 3-51, 4-57Max +dPo 3-51, 4-58Max -dPd 3-51, 4-58Max -dPo 3-51, 4-58Minimum Flow 3-92, 4-58Minimum Flow Control Enable 3-28–29, 4-59Minimum Flow Set Point 3-28, 4-59Minimum Pressure 3-92, 4-59Minimum Speed 3-92, 4-59

NN 3-17–19, 3-32, 3-71, 3-87, 3-92, 4-60N Offset 3-18–19, 4-60N Span 3-18–19, 4-60Net Flow Available 3-80, 4-60Not Running 3-92, 4-60Numerator 3-4, 4-60Numerator Mode 3-3–4, 3-6, 3-26–27, 3-31–32,3-69, 4-61

OOutput 3-30, 3-71–73, 3-77–78, 3-88, 4-61Output High Limit 3-71–72, 3-83, 3-87, 3-91, 4-61Output Low Limit 3-71–72, 3-76, 3-83, 4-62Output Reverse 3-73, 3-77, 4-62Output Tracking Rate 3-77, 4-62

April 20, 1998

Parameter Index–3

PP Offset 3-71, 4-62Pd 3-16–17, 3-20–21, 3-23, 3-28, 3-31, 3-50, 3-52,3-54, 3-62, 3-80, 3-92, 4-62Pd DGO Switch Level 4-63Pd Limit Enable 3-52, 3-54, 4-63, 5-4Pd Limit SP 3-52, 3-54–55, 4-63, 5-5Pd Limit SP Default 3-55, 4-63Pd Limit Status 3-52, 3-55, 4-64Pd Offset 4-64Pd PID DZ 3-39, 3-55, 4-64Pd PID Kd 3-55, 4-64Pd PID Ki 3-55, 4-64Pd PID Kp 3-55, 4-65Pd PID Tf 3-55, 4-65Pd Rate 3-50–51, 4-65Pd Samples 4-66Pd Span 3-38, 3-54, 3-62, 4-66PID Velocity High Limit 3-40–41, 3-54–56, 4-66PID Velocity Low Limit 3-40–41, 3-54–56, 4-66Pis 3-16, 3-23, 3-30, 4-66Pis Offset 4-67Pis Span 4-67POC 3-60–61, 3-88, 4-67POC CV 3-60, 3-62, 4-67POC CV LTOP 3-60, 4-67POC dCV 3-60, 4-67POC Enable 3-60–61, 4-68POC Filtered Delta 3-62, 4-68POC Filtered Delta Max 3-62, 4-68POC Filtered Gain 3-62, 4-68POC Filtered Threshold 3-62, 4-68POC PV Tf 3-62, 4-68POC Status 3-61, 4-69Pos 3-78, 4-69Pos Delta Delay 3-78, 4-69Pos Delta Max 3-78, 4-69Pos Feedback Reverse 3-78, 4-70Power EU 3-18, 4-70Pressure Channel 3-22–24, 3-80, 4-70Pressure EU and Pressure2 EU 3-18, 4-71Pressure Rate EU 3-18, 4-71Pressure->Flow Time Lag 3-51, 4-72Ps 3-16–17, 3-20–21, 3-23, 3-28, 3-32–33, 3-52,4-72Ps DGO Switch Level 4-72Ps Limit Enable 3-52–53, 4-72, 5-4Ps Limit PV 3-18, 3-52–53, 4-72Ps Limit SP 3-52–54, 4-73, 5-5 Ps Limit SP Default 3-54, 4-73Ps Limit Status 3-52, 3-54, 4-73Ps Offset 3-18–19, 4-73Ps PID DZ 3-39, 3-54, 4-74

Ps PID Kd 3-54, 4-74Ps PID Ki 3-54, 4-74Ps PID Kp 3-54, 4-74Ps PID Tf 3-54, 4-74Ps Span 3-18–19, 3-38, 3-53, 4-74Purge 3-86, 3-88, 4-75Purge Enable 3-86, 3-88, 4-75Purge Rate 3-87, 4-75Pvi 3-16, 3-23, 3-28, 4-75Pvi Offset 4-75Pvi Span 4-76

QQ Max 3-15, 3-78–79, 4-76Q Max Characterizer 3-79, 4-76Q Max Coefficient 3-79, 4-76Q Rec Out Characterizer 3-80, 4-77Q Rec Rc Characterizer 3-80, 4-77Q Recycle 3-15, 3-78–80, 4-77Q User 3-15, 3-78–80, 4-78Q User Coefficient 3-80–81, 4-78

RR 3-15, 3-20, 3-23–24, 3-67, 4-78RB Companions 3-67, 4-78RB CV LTOP 3-68, 4-79RB Rate 3-69, 4-79RB Valid 3-15, 3-68, 4-79RB Valid LTOP 3-68, 4-80Rc 3-17, 3-20–21, 3-25–26, 3-28, 3-31, 3-33, 3-52,3-55, 4-80Rc Limit Enable 3-52, 3-55, 4-80Rc Limit SP 3-52, 3-55–56, 4-80Rc Limit SP Default 3-56, 4-81Rc Limit Status 3-52, 3-56, 4-81Rc PID DZ 3-39, 3-56, 4-81Rc PID Kd 3-56, 4-81Rc PID Ki 3-56, 4-81Rc PID Kp 3-56, 4-82Rc PID Tf 3-56, 4-82Rc Span 3-38, 3-55, 4-82Recycle Trip Test 3-47, 4-82Remote Low Clamping 3-73, 4-82RT 3-43, 3-46, 3-59, 4-82RT Count 3-43, 4-83RT Deadtime 3-43–44, 4-83RT Derivative Response Enable 3-43–44, 4-83RT Distance 3-11, 3-42, 4-83RT dSs Delay 3-45, 4-83RT dSs Level 3-45, 4-84RT dSs Response 3-45, 4-84RT Kd 3-44–45, 4-84RT Kp 3-44–45, 4-84


Parameter Index–4

RT Max Amplitude 3-43–45, 4-85RT Status 3-47, 4-85Running 3-15, 3-87, 3-92, 4-85

SS 3-12, 3-15, 3-20, 3-32–33, 3-58, 3-66–67, 3-70,4-85S Calc Updated 3-12, 4-86S Control Start Level 3-71, 4-86S Control Start Speed 3-71, 4-86S Control Stop Speed 3-71, 4-86S Controller Companions 3-69, 4-86S Failure 3-30, 4-87S Tf 3-3, 3-41, 4-87Selected I 3-15, 3-58, 3-70, 4-87Selected P 3-15, 3-58, 3-70, 4-88Series 3-57, 3-86–88, 3-91, 4-88Shutdown Manual Enable 3-86, 3-89, 4-88Side Stream Comp Mode 3-22, 3-25–26, 4-89Side Stream Companion 3-25, 3-27, 4-89Sigma 3-17, 3-20–21, 3-30–33, 4-90Sigma Tf 3-21, 4-90SO 3-15, 3-48–49, 4-90SO b4 3-10, 3-48–49, 4-90SO b4 Rate 3-49, 4-91SO Bias 3-10, 3-48, 3-71, 4-91SO Dead Time 3-49, 4-91SO Distance 3-11, 3-47–48, 4-91SO Initial 3-10, 3-42, 3-48, 3-71, 4-92SO Time Based Enable 3-49, 4-92Ss 3-3, 3-12, 3-20, 3-28, 3-41–42, 3-44, 4-92Ss Samples 4-93Start Rate 3-71, 3-88, 3-91, 4-93Startup Time 3-92, 4-93State 3-84, 4-93Status 3-15, 3-58, 3-60, 3-63, 3-70, 3-79, 4-94Stop 3-46, 3-86–91, 4-94Stop Enable 3-86–88, 4-94Stop Rate 3-87, 3-91, 4-94Stop Status 3-86, 4-94Stop Time 3-92, 4-95Suction Pressure EU and Suction Pressure2 EU3-18, 4-95Surge Count 3-10, 3-42, 3-48–51, 4-95, 5-3Surge Count Reset 3-49–50, 4-96, 5-7Surge Count Shutdown Reset 3-50, 4-96Surge DZ 3-39, 3-41, 4-96Surge Ki 3-41, 3-46, 4-96Surge Kp 3-41, 4-96Surge Relay Threshold 3-50, 4-96Surges 3-50, 4-97

TT Air 3-17, 4-97T Air Gain 4-97T Air Normal 4-97T CW 3-17T CW 4-97T CW Gain 4-97T CW Normal 4-97T Ratio 3-20, 3-25, 3-29, 3-31–32, 4-97Tac 3-17, 3-23, 3-31, 4-98Tac Offset 4-98Tac Span 4-98Td 3-16–17, 3-20–21, 3-23, 3-31–32, 3-80, 4-98Td DGO Switch Level 4-98Td Offset 4-98Td Span 4-98Temperature Based Hp Enable 3-29, 4-99Temperature Channel 3-22–24, 3-80, 4-99Temperature EU and Temperature2 EU 3-18, 4-99Tight Shut Off Distance 3-11–12, 3-76, 4-100Tis 3-17, 3-23, 3-30, 4-100Tis Offset 4-100Tis Span 4-100Track 4-100Ts 3-16–17, 3-20–21, 3-23, 3-32, 4-100Ts Offset 4-100Ts Span 4-101

UUp 3-89, 4-101User 4-101User Offset 4-101User Span 4-101

VValve Characterizer 3-75, 4-101Valve Dead Band Bias 3-75, 4-102Valve Dead Band Bias Threshold 3-76, 4-102Valve Mode 3-73, 4-102Valve Sharing Companions 3-57, 4-103Valve Sharing Mode 3-57, 4-103Variable List 4-104VS 3-58–59, 4-104VS CV LTOP 3-58, 4-104VS I LTOP 3-58, 3-70, 4-104VS P LTOP 3-58, 3-70, 4-104VS RT 3-59, 4-104VS S LTOP 3-58, 3-70, 4-105VS Status 3-59, 4-105

April 20, 1998

July 30, 1997 UM4102 (3.0)

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Document Evaluation FormPublication Title: Using the Series 4 Antisurge Controller

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