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EMERSON Process Management Educational Services Copyrighted Material / Duplication ProhibitedAdvanced Tools & Techniques
Advanced Tools & TechniquesAdvanced Tools & Techniques
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IntroductionIntroduction
Over the last 10 years significant improvements made in advanced control tool capabilities and in user interfaces, improvements that make it easier to design and commission advanced control solutions.
Also since then, new advanced control applications have been introduced for batch and continuous processes.
The book Advanced Control Foundation – Tools, Techniques, and Applications provides a fresh look at some of the latest advanced control technologies that are available to the process industry. A web site for the book allows the solutions to the book’s workshops to be viewed using a web browser.
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Areas to be AddressedAreas to be AddressedThis session will provide an overview of the more common technique that may be used to improve process operations. Areas that will be addressed are:
• Evaluating Control System Performance (Demo)
• Tuning - Integrating Process, Units Conversion(Workshop),
• Intelligent PID (demo)
• Adaptive Tuning
• Fuzzy Logic Control
• Property Estimation - Neural Networks(NN) and Other Technique
• Model Predictive Control (MPC) with Optimization
• Integrating Advanced Control Into an Older DCS
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Basis for Presentation Basis for Presentation Material that will be presented is based on Advanced Control Foundation.
This book was published in Sept 2012 by ISA and addresses the advanced control products in the DeltaV control system (or targeted for a future DeltaV release).
The book may be purchased on-line through ISA or Amazon.
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Basis for Presentation (Cont)Basis for Presentation (Cont)The solution to workshop included in the book may be viewed using your web browser- see http://www.advancedcontrolfoundation.com/
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Evaluating Control System PerformanceEvaluating Control System Performance
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Plant Operating performancePlant Operating performanceThe latest UI technology allows the plant operator to do more.
Graphic displays and historic trends allow the operator to view and interact with discrete and continuous control
Operator must depend on the control system to maintain target operating condition to achieve best performance.
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Issues Confronting The Process IndustryIssues Confronting The Process Industry
In many cases the staffing at the plant level has been reduced. Plant support at the corporate level may have been severely downsized or eliminated.
Process engineers and instrumentation technicians may not have sufficient training to fully understand control setup and tune PID loops for best performance.
Resources at the plant level may only be sufficient to address issues that disrupt production.
The impact of control utilization/performance may not be monitored, documented and/or effectively communicated to plant management.
This is a global issue – Not specific to the control system manufacturer, commonly encountered in many major plants located in the US, Europe, Asia Pacific, Middle East.
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Evaluating Control System Performance (Cont)Evaluating Control System Performance (Cont)A plant equipped with the latest control systems and field instrumentation may still be found to have low control utilization.
Often the key to getting control loops back on automatic is for plant management to be aware of the low control utilization and its impact on product quality and production rate.
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Performance MonitoringPerformance Monitoring
Measurement status and control mode as defined by IEC61804 are key to performance monitoring
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Performance Monitoring - ExamplePerformance Monitoring - ExampleDeltaV Insight allows easy navigation of control hierarchy
Overview display summarizes performance for System, Area, Units and Modules
Abnormal Control Conditions indicated for Problem Loops:
• Control Service Status:
− Incorrect mode− Limited control output− Bad/Uncertain input
• Control Performance Status:
− Standard Deviation− Variability Index− Oscillation Index− Tuning Index
• Device and Valve Diagnostics
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Process Area OverviewProcess Area Overview
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Summary View of a ProcessSummary View of a Process
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Module ViewModule View
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Detail View of Block PerformanceDetail View of Block Performance
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Performance Reports - ExamplePerformance Reports - Example
Report generation is an important feature of performance monitoring tools.
Reports can be used to gain the management support that is required to address low control utilization or to determine the source of excessive process variation that impacts production or product quality
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Resolving Problems that Impact Control UtilizationResolving Problems that Impact Control Utilization
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Resolving Problems that Impact Process VariationResolving Problems that Impact Process Variation
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EMERSON Process Management – Educational Services Advanced Tools & Techniques
On-Demand TuningOn-Demand Tuning
Where low control utilization is due to PID tuning, then On-demand tuning may be used to commission the loop. May be quickly applies
Captures process dynamics in the field (controller or device) to allow better process identification, particularly for the fastest loops.
May be used to tuning PID for control of self-regulating and integrating processes
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Advanced Tools – Entech ToolkitAdvanced Tools – Entech Toolkit
Not normally required. Some customers (pulp and paper industry) have adopted this tool.
May be used by specialist trained on this tool to identify and resolve causes of process variation and loop interaction.
Advanced tuning techniques may be applied when addressing complex process dynamics.
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Tuning - Integrating Process, Units Conversion Tuning - Integrating Process, Units Conversion
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DeltaV On-Demand TuningDeltaV On-Demand Tuning
May be used to tune PID used for control of a self-regulating process or an integrating process.
Especially helpful for tuning integrating processes or processes characterized by slow dynamics.
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DeltaV On-demand Tuning (Cont)DeltaV On-demand Tuning (Cont)
When the on-demand tuning application resides in a DCS workstation, communications between the controller and the workstation can introduce variable delay and jitter in the observed process response.
To allow the process to be accurately identified, the on-demand tuning in DeltaV is distributed between the workstation and the controller/ field device.
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Manually Tuning an Integrating ProcessManually Tuning an Integrating Process
Manual tuning is complicated by the fact that it is difficult to establish process characterization from step response because of changing process conditions that prevent establishing a steady state condition.
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Manually Tuning an Integrating ProcessManually Tuning an Integrating Process
Simple two step procedure:
1. Set the integral gain based on the process deadtime and the desired closed loop response i.e. the time required for the PV to reach 63% of change in Setpoint when in Automatic control. (based on Skogestad’s rule)
Where:
2. Adjust the proportional gain to achieve the desired response (making no adjustment in the reset setting made in step 1.
Note: The specified closed loop response time must be physically achievable under normal operating conditions without the manipulated parameter saturating.
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System Migration - Equivalent DeltaV TuningSystem Migration - Equivalent DeltaV Tuning
When an older system is replaced with DeltaV then if the tuning units of the older system are different than those used in deltaV, then it will necessary to convert the tuning from the older system to the equivalent tuning in DeltaV.
An Excel spreadsheet has been created to automatically do this conversion from Provox tuning to equivalent DeltaV tuning.
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WorkshopWorkshop
1. Open the workspace for the Three Element Level Control application. Change the setpoint and observe the response using the chart. Adjust the reset tuning to provide a slower closed loop response. Change the setpoint observe the response using the chart.
2. Install on your laptop the Excel spreadsheet for conversion of Provox tuning to equivalent DeltaV Tuning.
3. Enter the following Provox tuning and examine the equivalent DeltaV tuning.
• Loop Tag: FIC110
• Proportional Gain: 0.4
• Reset: 30 repeats/min
• Rate: 0
4. Examine the equations that are used for the units conversion.
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Three Element Level ControlThree Element Level Control
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Intelligent PIDIntelligent PID
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PIDPlus Feature of DeltaV PIDPIDPlus Feature of DeltaV PID
The PIDPlus feature of the DeltaV PID (DeltaV v11 and higher) is enabled through the FRSIPID_OPTS parameter.
When PIDPlus is enabled then special behavior is provided to address:
• Control using Wireless measurement or sampled inputs provided by an anlayzer
• Recovery from process saturation conditions.
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PIDPlus for Wireless ControlPIDPlus for Wireless Control
The Challenge – Control Using Wireless
Transmitter power consumption is minimized by reducing the number of times the measurement value is communicated.
Conventional PID execution synchronizes the measurement value with control action, by over-sampling the measurement by a factor of 2-10X.
The rule of thumb to minimize control variation is to have feedback control executed 4X to 10X times faster than the process response time (process time constant plus process delay).
The conventional PID design (i.e., difference equation and z-transform) assumes that a new measurement value is available at each execution and that control is executed on a periodic basis.
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Conventional Approach – Over Sampling of MeasurementConventional Approach – Over Sampling of Measurement
Control Execution
63% of Change
Process Output
Process Input
Deadtime (TD )
O
I
New Measurement Available
Time Constant ( )
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Conventional PID - Impact of WirelessConventional PID - Impact of Wireless
The underlying assumption in traditional control design is that the PID is executed on a periodic basis.
When the measurement is not updated on a periodic basis, the calculated reset action may not be appropriate.
If control action is only executed when a new measurement is communicated, this could result in a delayed control response to setpoint changes and feedforward action on measured disturbances.
Conventional PID Design
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*WirelessHART Communication*WirelessHART Communication
Window communication is the preferred method of communications for control applications. A new value will be communicated only if:
• The magnitude of the difference between the new measurement value and the last communicated measurement value is greater that a specified trigger value
• or if the time since the last communication exceeds a maximum update period.
Thus, the measurement is communicated only as often as required to allow control action to correct for unmeasured disturbances or response to setpoint changes.
For Windowed mode you must specify an update period, a maximum update period, and a trigger value.
*HART 7 specification that has been adopted as an international standard, IEC 62591Ed. 1.0.
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PID Modification for Wireless ControlPID Modification for Wireless ControlTo provide the best control for a non-periodic measurement, the PID must be modified to reflect the reset contribution for the expected process response since the last measurement update.
Control execution is set faster than measurement update. This permits immediate action on setpoint change and update in faceplate.
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PIDPlus Using Wireless Transmitter vs. Conventional PID and Wired TransmitterPIDPlus Using Wireless Transmitter vs. Conventional PID and Wired Transmitter
Control
Measurement
Control Output
Unmeasured
Disturbance
Setpoint PIDPlus
PIDPlus
PID
PID
Lambda Tuning ʎ = 1.0
Communication Resolution = 1%
Communication Refresh = 10sec
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Control Performance DifferenceControl Performance Difference
Communications transmissions are reduced by over 96 % when window communication is utilized.
The impact of non-periodic measurement updates on control performance as measured by Integral of Absolute Error (IAE) is minimized through the PID modifications for wireless communication.
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PIDPlus - Modified Derivative ActionPIDPlus - Modified Derivative Action
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PID Performance for Lost CommunicationsPID Performance for Lost Communications
The Conventional PID provides poor dynamic response when wireless communications are lost.
The PID modified for wireless control provides improved dynamic response under these conditions
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Wireless Communication Loss – During Setpoint ChangeWireless Communication Loss – During Setpoint Change
Communication Loss
PID
PIDPlus
PIDPlus
PID
Control
Measurement
Control Output
Setpoint
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Wireless Communication Loss – During Process DisturbanceWireless Communication Loss – During Process Disturbance
Communication Loss
PIDPlus
Setpoint Control
Measurement
Control Output
PID
PIDPlus
PID
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Installation at Broadley JamesInstallation at Broadley JamesPortable Hyclone 100 liter disposable bioreactor
Rosemount WirelessHART gateway and transmitters for measurement and control of pH and temperature. Pressure monitored
BioNet is based on the DeltaV Control system.
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Broadley James Bioreactor SetupBroadley James Bioreactor Setup
Bioreactor
VSD
VSD
TC 41-7
AT 41-4s2
AT 41-4s1
AT 41-2
AT 41-1
TT 41-7
AT 41-6
LT 41-14
Glucose
Glutamine
pH
DO
Product
Heater
VSD
VSD
VSD
AC 41-4s1
AC 41-4s2
Media
Glucose
Glutamine
VSD
Inoculums
VSD
Bicarbonate
AY 41-1
AC 41-1Splitter
AC 41-2
AY 41-2Splitter
CO2
O2
Air
Level
Drain
0.002 g/L
7.0 pH
2.0 g/L
2.0 g/L
37 oC
MFC
MFC
MFC
AT 41-5x2
Viable Cells
AT 41-5x1
Dead Cells
Bioreactor
VSDVSD
VSD
TC 41-7TC
41-7
AT 41-4s2
AT 41-4s1
AT 41-2
AT 41-1
TT 41-7
AT 41-6
LT 41-14
Glucose
Glutamine
pH
DO
Product
Heater
VSD
VSD
VSD
AC 41-4s1
AC 41-4s1
AC 41-4s2
AC 41-4s2
Media
Glucose
Glutamine
VSD
Inoculums
VSD
Bicarbonate
AY 41-1
AC 41-1AC
41-1Splitter
AC 41-2AC
41-2
AY 41-2Splitter
CO2
O2
Air
Level
Drain
0.002 g/L
7.0 pH
2.0 g/L
2.0 g/L
37 oC
MFC
MFC
MFC
AT 41-5x2
Viable Cells
AT 41-5x1
Dead Cells
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Wireless Temperature Loop Test ResultsWireless Temperature Loop Test Results
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Wireless pH Loop Test ResultsWireless pH Loop Test Results
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Separations Research Program, University of Texas at Austin
The Separations Research Program was established at the J.J. Pickle Research Campus in 1984
This cooperative industry/university program performs fundamental research of interest to chemical, biotechnological, petroleum refining, gas processing, pharmaceutical, and food companies.
CO2 removal from stack gas is a focus project for which WirelessHART transmitters were installed for pressure and steam flow control
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Steam Flow To Stripper Heater
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Column Pressure Control
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PC215 On-line Column Pressure Control
The same dynamic control response was observed for SP changes
Original plant PID tuning was used for both wired and wireless control
GAIN=2.5
RESET=4
RATE=1
Wired Measurement Used
in Control
Wireless Measurement
Used in Control
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Control Performance – Wired vs WirelessComparable control as measured by IAE was achieved using WirelessHART Measurements and PIDPlus vs. control with wired measurements and PID.
The number of measurement samples with WirelessHART vs Wired transmitter was reduced by a factor of 10X for flow control and 6X for pressure control – accounting for differences in test duration.
Test #1 Test #2
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Recovery From Process SaturationRecovery From Process Saturation
The recovery of the PID from process saturation is critical in many continuous and batch applications.
By utilizing a variable preload when the PID output is limited for an extended period of time (process saturation), it is possible to minimize setpoint overshoot on recovery from saturation.
PI Control with Variable Pre-load
PI Control
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PIDPlus for Recovery From Process Saturation
The PIDPlus option in DeltaV v11 provides improved the control response for recovery from process saturation.
• PIDPlus option added in DeltaV v11.3 to improve control response for recovery from process saturation. Anticipation action can be adjusted using the PID parameter RECOVERY_FILTR. Value of 1 = No anticipation, Value of 0 = full anticipation utilized to avoid SP overshoot when recovering from process saturation
• The benefit of enabling the PIDPlus option will be shown using several process examples. Application of PIDPlus in Surge Control will be examined in detail based on “typical” centrifugal air compressor used in refining industry.
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PIDPlus – Addressing Process Saturation
A process saturation condition exists when the setpoint of a PID can not be maintained and the PID output is limited.
Three examples will be used to illustrate process saturation conditions :
• Steam header pressure control
• Boiler outlet steam temperature control.
• Compressor surge Control
When operating conditions change that allow the process to recover from a process saturation condition, then improved response is provided by enabling the FRSIPID_OPTS option for PIDPlus. Anticipation action can be adjusted using the PID parameter RECOVERY_FILTR. Value of 1 = No anticipation, Value of 0 = full anticipation utilized to avoid SP overshoot when recovering from process saturation
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Example – Steam Temperature Control using PIDPlusExample – Steam Temperature Control using PIDPlus
If steam generation exceeds the attemperator capacity then the boiler outlet steam temperature will exceed the outlet setpoint with the spray valve fully open.
When boiler firing rate is reduced, then the spray value should be cut back as the outlet temperature drops.
When the FRSIPID_OPTS for PIDPlus is enabled then the valve moves before PV reached SP – providing improved response.
Standard PID DeltaV PIDPlus
SP Overshoot
50% Drop in steam
generation
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Example - Header Pressure ControlExample - Header Pressure ControlUnder normal operating conditions the pressure reducing valve, PV196, remains close and the 400# header pressure is maintained by the steam turbine extraction.
If the turbine extraction can not meet 400# steam demand or the turbine trips off-line then the PRV valve must open to maintain header pressure.
A very small improvement in response for a 40% drop in turbine extraction is seen since for this example the PV normally operates close to SP.
Standard PID DeltaV PIDPlus
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Compressor Surge ControlCompressor Surge Control
Single-shaft centrifugal compressors with horizontally split casings are commonly used in the process industry
Are preferred for applications requiring medium pressures and large volume e. g. cracked gas, coker gas, process air or carbon dioxide.
Electric or steam turbine drive design.
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Compressor SurgeCompressor SurgeSurge* is the point at which the compressor peak head capability and minimum flow limit are reached. If the operating point approaches the surge line, the impeller and diffuser begin to operate in stall and flow recirculation occurs.
The flow separation will eventually cause a decrease in the discharge pressure and flow from suction to discharge will resume. This surge cycle will repeat itself unless control system brings the compressor out of the surge cycle.
Any surge event can cause severe damage to the thrust bearings, seals, and the impeller.
*GMRC Guideline –Version 4.3 Application Guideline for Centrifugal
Compressor Surge Control Systems
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Control RequirementsControl RequirementsThe primary objective of a surge control system is to prevent the occurrence of surge so as to reduce possible damage to the compressor The three primary operating environments for the surge control system are:
Start-up Environment - In a typical start-up mode, gas is continually recycled to bring the compressor online. The recycle valve is fully opened upon start-up. As the compressor begins to gain speed and flow is increased, the recycle valve is gradually closed.
Normal Process Control Environment –The surge control system must provide for smooth operation of the compressor over the entire operating range. The shape of the surge control line will determine the response characteristics of the surge control system. Precision in recycle valve position control and minimizing overshoot are required.
Emergency Shutdown Environment - The surge control system must function quickly to open the recycle valve fully
We will address the normal process control environment.
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Typical Air CompressorTypical Air Compressor
The surge control system acts as an integral part of the compressor station controls.
The recommended margin allowed between the actual surge line and the surge control line is 6-10 percent of the actual flow surge limit.
Note: The scaling of the compressor performance curve has been
normalized to protect the real plant data.
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Air Compressor – Normal OperationsAir Compressor – Normal OperationsThe function of the surge control system is to detect the approach to surge and provide more flow to the compressor through opening the recycle valve to avoid surge.
Opening of the vent valve provides more flow and reduces compressor head, to move the compressor away from its surge point.
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Dynamic Compressor Simulation Dynamic Compressor Simulation A dynamic compressor simulation that matches typical BP air compressor data was developed to support testing of the compressor controls.
The simulation was tied to the control strategy used for normal operation.
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Air Compressor Control – Normal OperationsAir Compressor Control – Normal Operations
Parameters were added to support testing
• Normal Load Demand
• Process status
• Motor status
BP Tuning for typical compressor was utilized
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Control Response – PIDPlus DisabledControl Response – PIDPlus Disabled
Surge Margin
60% Reduction in
Air Demand
Surge Line Exceeded
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Control Response – PIDPlus EnabledControl Response – PIDPlus Enabled
Surge Margin
60% Reduction in
Air Demand
Surge Margin Maintained
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Learning More About PIDPlusLearning More About PIDPlus• The module that is used in the Intelliegent PID workshop may be downloaded from the
Advanced Control Foundation web site and imported on any DeltaV system (v11 or higher).
• Allows performance of PIDPlus using wireless measurement to be compared to PID with wired measurement
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Adaptive ControlAdaptive Control
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On-demand Tuning (Cont)On-demand Tuning (Cont)
When using an on-demand tuning application, consider that the process gain may change with the operating conditions.
For robust control, tuning should be based on the operating conditions that provide maximum process gain.
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Adaptive TuningAdaptive Tuning
In some cases, the tuning established at one operating point may not provide the best control for the full operating range.
Adaptive tuning allows the process gain and dynamics to be automatically identified and used in control.
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Adaptive Control - ImplementationAdaptive Control - Implementation
To allow the data used in adaptive control to be collected without communication skew or jitter, adaptive control is implemented directly in the DeltaV PID
Enables adaptive control to be utilized even in high speed control applications.
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Adaptive TuningAdaptive TuningAllows tuning the process model to be automatically established based on:
• Normal setpoint changes made by the operator when the PID is in an automatic
• PID output changes when the PID is in a manual mode.
Model switching with re-centering and interpolation may be used for process model identification.
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Viewing Identified ModelsViewing Identified Models
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View Adaptive Tuning Solution
Advanced Control Foundation web site
http://www.advancedcontrolfoundation.com/adaptive-tuning-solution.aspx
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Fuzzy Logic ControlFuzzy Logic Control
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Predefined Fuzzy Logic Control Function BlockPredefined Fuzzy Logic Control Function Block
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Fuzzy Logic ControlFuzzy Logic ControlFor some specific process applications, fuzzy logic control enables faster setpoint recovery with less overshoot than PID control for both setpoint and load changes
Fuzzy logic is best suited for controlling processes characterized by large time constants and little or no deadtime
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Fuzzy Logic Control WorkshopFuzzy Logic Control Workshop
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Property EstimationProperty Estimation
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Neural Networks for Property EstimationNeural Networks for Property Estimation
When a product quality measurement is available only from the lab, it is often possible to use upstream measurements to calculate an estimated value.
To address the non-linear response of product quality parameters to changes in process inputs, the estimator can be based on a neural network model.
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Continuous Digester ExampleContinuous Digester Example
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Batch and Continuous Data AnalyticsBatch and Continuous Data Analytics
Through the use of on-line data analytics, it is possible to provide:
• Product quality predictions which allow quality problems to be identified while there is time to take corrections action.
• Detection of abnormal process operation and/or equipment problems and support of root cause analysis
Batch Analytics in DeltaV v12, Continuous Analytics currently under development.
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Continuous Example – Static MixerContinuous Example – Static Mixer
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Batch ExampleBatch Example
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Model Predictive ControlModel Predictive Control
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Model Predictive Control(MPC) in DeltaVModel Predictive Control(MPC) in DeltaV
Three versions of Model Predictive Control (MPC) are provided in DeltaV.
• DeltaV Predict (DeltaV v7 or later) – Addresses processes as large as 8x8. Pusher capability is provided to allow process throughput to be maximized by maintaining the process at its operating constraint. No cost if only one(1) manipulated parameter. Module runs in Controller or Application station.
• DeltaV PredictPro DeltaV v9 or later) - For larger, more complex process as large as 40x80 . Linear Program (LP) embedded to support process optimization based on user defined control objective. Module runs in Controller or Application station.
• DeltaV PedictPlus (DeltaV v12 or later)– Adds greater capability to address changing operating constraint and integrating processes. Module runs only in Application station.
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Replacing PID with MPCReplacing PID with MPCDeltaV Predict may be used to replace PID when the process is characterized by large deadtime, multiple measured distrubances or constaints.
• No cost if only one manipulated parameter.
• Designed to be layered on top PID in existing control strategy.
One Measured Disturbance Input
MPC Constraint Control
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Simple MPCSimple MPC
MPC has proven advantages over multi-loop PID control techniques in a variety of small applications that are characterized by:
• Long process delay and interaction,
• Measured disturbances or constraints
• Production is limited by process input(s)
Embedded MPC capability in the control system.is an advantage
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MPC Integrated with OptimizationMPC Integrated with OptimizationFor larger, more complex applications that are used in batch or continuous processing, the plant operation objective(s) may be best met using MPC integrated with optimization i.e. DeltaV PredictPro.
Such applications are often characterized by numerous operating constraints and the need to address broader operating objectives, such as maximizing throughput while minimizing production costs
MEE Process
CTMP Process
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CTMP Refiner Process Step ResponseCTMP Refiner Process Step Response
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Example: Lime Kiln Control – DeltaV PredictExample: Lime Kiln Control – DeltaV Predict
View the following videos showing the DeltaV Predict installation at Canfor Pulp and Paper. These videos are good examples of the types of videos contained on the DeltaV web site under Video Central.
http://www.youtube.com/watch?v=IwPFqLgh21M
http://www.youtube.com/watch?v=sNlosWA8crE
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Integrating Advanced Control Into an Older DCSIntegrating Advanced Control Into an Older DCS
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Integrating Advanced Control Into a DCSIntegrating Advanced Control Into a DCS
When advanced control is embedded in the distributed control system (DCS), the plant operator has a single window interface with consistent system interaction and single log-in and span of control.
If the DCS does not support advanced control, then the advanced control applications must be layered onto the DCS. Several approaches may be taken depending on the DCS support for layered applications.