Slide 1 Interactive Opportunity Interactive Opportunity Assessment Assessment Demo and Seminar (Deminar) Series for Web Labs – PID Control of True Integrating PID Control of True Integrating Processes Processes Aug 11, 2010 Sponsored by Emerson, Experitec, and Mynah Created by Greg McMillan and Jack Ahlers www.processcontrollab.com Website - Charlie Schliesser (csdesignco.com
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PID Control of True Integrating Processes - Greg McMillan Deminar
Presented August 11, 2010 by Greg McMillan as on-line demo/seminar. Video recording available at: http://www.screencast.com/users/JimCahill/folders/Public
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PID Control of True Integrating PID Control of True Integrating Processes Processes
Aug 11, 2010Sponsored by Emerson, Experitec, and Mynah
Created byGreg McMillan and Jack Ahlers
www.processcontrollab.com Website - Charlie Schliesser (csdesignco.com)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 2 Slide 2
WelcomeWelcome WelcomeWelcome Gregory K. McMillan
– Greg is a retired Senior Fellow from Solutia/Monsanto and an ISA Fellow. Presently, Greg contracts as a consultant in DeltaV R&D via CDI Process & Industrial. Greg received the ISA “Kermit Fischer Environmental” Award for pH control in 1991, the Control Magazine “Engineer of the Year” Award for the Process Industry in 1994, was inducted into the Control “Process Automation Hall of Fame” in 2001, was honored by InTech Magazine in 2003 as one of the most influential innovators in automation, and received the ISA “Life Achievement Award” in 2010. Greg is the author of numerous books on process control, his most recent being Essentials of Modern Measurements and Final Elements for the Process Industry. Greg has been the monthly “Control Talk” columnist for Control magazine since 2002. Greg’s expertise is available on the web site: http://www.modelingandcontrol.com/
[File Name or Event]Emerson Confidential27-Jun-01, Slide 3 Slide 3
Top Ten Reasons to Elect a Control Top Ten Reasons to Elect a Control Engineer as a PresidentEngineer as a President
Top Ten Reasons to Elect a Control Top Ten Reasons to Elect a Control Engineer as a PresidentEngineer as a President
(10) Completely automated and remotely controlled combat (9) Dynamic programs (8) Models of the economy (7) No overshoot of the budget (6) Real time optimization of manufacturing (5) Regulatory control of financial markets (4) Feedforward control of Congress (3) Model predictive control of energy (2) A nuclear reactor in every home
And the Number 1 Reason:
[File Name or Event]Emerson Confidential27-Jun-01, Slide 4 Slide 4
Top Ten Reasons to Elect a Control Top Ten Reasons to Elect a Control Engineer as a PresidentEngineer as a President
Top Ten Reasons to Elect a Control Top Ten Reasons to Elect a Control Engineer as a PresidentEngineer as a President
(1) A computer in every pocket
[File Name or Event]Emerson Confidential27-Jun-01, Slide 5 Slide 5
Demos of Control Loop OpportunitiesDemos of Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup TimeDemos of Control Loop OpportunitiesDemos of Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup Time
PID on Error Structure– Maximizes the kick and bump of the controller output for a setpoint change. – Overdrive (driving of output past resting point) is essential for getting slow loops,
such as vessel temperature and pH, to the optimum setpoint as fast as possible.– The setpoint change must be made with the PID in Auto mode.– “SP track PV” will generally maximize the setpoint change and hence the kick
and bump (retaining SP from last batch or startup minimizes kick and bump) SP Feedforward
– For low controller gains (controller gain less than inverse of process gain), a setpoint feedforward is particularly useful. For this case, the setpoint feedforward gain is the inverse of the dimensionless process gain minus the controller gain.
– For slow self-regulating (e.g. continuous) processes and slow integrating (e.g. batch) processes, even if the controller gain is high, the additional overdrive can be beneficial for small setpoint changes that normally would not cause the PID output to hit a limit.
– If the setpoint and controller output are in engineering units the feedforward gain must be adjusted accordingly.
– The feedforward action is the process action, which is the opposite of the control action, taking into account valve action. In other words for a reverse control action, the feedforward action is direct provided the valve action is inc-open or the analog output block, I/P, or positioner reverses the signal for a inc-close.
[File Name or Event]Emerson Confidential27-Jun-01, Slide 6 Slide 6
Demos of Control Loop OpportunitiesDemos of Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup TimeDemos of Control Loop OpportunitiesDemos of Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup Time
Full Throttle (Bang-Bang Control) - The controller output is stepped to it output limit to maximize the rate of approach to setpoint and when the projected PV equals the setpoint less a bias, the controller output is repositioned to the final resting value. The output is held at the resting value for one deadtime. For more details, check out the Control magazine article “Full Throttle Batch and Startup Response.” http://www.controlglobal.com/articles/2006/096.html
– A deadtime (DT) block must be used to compute the rate of change so that new values of the PV are seen immediately as a change in the rate of approach.
– If the total loop deadtime (o) is used in the DT block, the projected PV is simply the current PV minus the output of the DT block (PV) plus the current PV.
• If the PV rate of change (PV/t) is useful for other reasons (e.g. near integrator or true integrating process tuning), then PV/t = PV/o can be computed.
– If the process changes during the setpoint response (e.g. reaction or evaporation), the resting value can be captured from the last batch or startup
– If the process changes are negligible during the setpoint response, the resting value can be estimated as:
• the PID output just before the setpoint change for an integrating (e.g. batch) process• the PID output just before the setpoint change plus the setpoint change divided by the
process gain for a self-regulating (e.g. continuous) process
– For self-regulating processes such as flow with the loop deadtime (o) approaching or less than the largest process time constant (p ), the logic is revised to step the PID output immediately to the resting value. The PID output is held at the resting value for the T98 process response time (T98 o p ).
[File Name or Event]Emerson Confidential27-Jun-01, Slide 7 Slide 7
[File Name or Event]Emerson Confidential27-Jun-01, Slide 9 Slide 9
CV change in controlled variable (%) CO change in controller output (%) Kc controller gain (dimensionless)
Ki integrating gain (%/sec/% or 1/sec)
Kp process gain (dimensionless) also known as open loop gain MV manipulated variable (engineering units) PV process variable (engineering units) t change in time (sec)
ototal loop dead time (sec)
mmeasurement time constant (sec)
pprocess time constant (sec) also known as open loop time constant
Ti integral (reset) time setting (sec/repeat)
Td derivative (rate) time setting (sec)
To oscillation period (sec)
Lambda (closed loop time constant or arrest time) (sec)
fLambda factor (ratio of closed to open loop time constant or arrest time)
NomenclatureNomenclature NomenclatureNomenclature
[File Name or Event]Emerson Confidential27-Jun-01, Slide 10 Slide 10
2. PI action on error, D action on PV (= 1 and = 0)
3. I action on error, PD action on PV (= 0 and = 0)
4. PD action on error (= 1 and = 1) (no I action)
5. P action on error, D action on PV (= 1 and = 0) (no I action)
6. ID action on error ( = 1) (no P action)
7. I action on error, D action on PV ( = 0) (no P action)
8. Two degrees of freedom controller (and adjustable 0 to 1)
The and factors do not affect the load response of a control loop
[File Name or Event]Emerson Confidential27-Jun-01, Slide 12 Slide 12
Contribution of Each PID Mode Contribution of Each PID Mode (Step Change in the Set Point)(Step Change in the Set Point)
Contribution of Each PID Mode Contribution of Each PID Mode (Step Change in the Set Point)(Step Change in the Set Point)
CO2 = CO1
SP
seconds/repeatCO1
Time(seconds)
Signal (%)
0
kick fromproportional
mode
bump fromfiltered
derivativemode
repeat from integralmode
For fastest setpoint response we want to maximize kick from proportional mode bump from derivative mode, and setpoint weighting factors (= 1 and = 1)
[File Name or Event]Emerson Confidential27-Jun-01, Slide 13 Slide 13
Lambda Tuning for Lambda Tuning for Integrating ProcessesIntegrating ProcessesLambda Tuning for Lambda Tuning for
Integrating ProcessesIntegrating Processes
Integrating Process Gain:
Controller Gain:
Controller Integral (Reset) Time:
Lambda (closed loop arrest time) is defined in terms of a Lambda factor (f):
if K/ Closed loop arrest timefor load disturbance
CO
tCVtCVKi %
/%/% 1122
2])/[( oifi
ic KK
TK
oifi KT )/(2
Controller Derivative (Rate) Time:
pdT
To prevent slow rolling oscillations:
iic KTK
2*
secondary lag
[File Name or Event]Emerson Confidential27-Jun-01, Slide 14 Slide 14
Primary and secondary Kp secondary p primary p totalo
Ki Kp p
2 pdT
Tuning for Today’s ExampleTuning for Today’s ExampleTuning for Today’s ExampleTuning for Today’s Example
1f
21010)01.0/1(2)/(2 oifi KT
7.1]10)01.0/1[(01.0
210
])/[( 22
oifi
ic KK
TK
01.0
2210*7.1
[File Name or Event]Emerson Confidential27-Jun-01, Slide 15 Slide 15
Demo of Effect of PID Structure 3Demo of Effect of PID Structure 3on Setpoint Responseon Setpoint Response
Demo of Effect of PID Structure 3Demo of Effect of PID Structure 3on Setpoint Responseon Setpoint Response
Objective – Show slow setpoint response from just integral action
Activities:– For Single Integrating Loop:
• Enter tuning settings, Gain = 1.7, Reset = 210 sec, Rate = 2 sec
• Set Primary Process Delay = 9 sec, Lag 2 Inc & Lag 2 Dec = 100 sec
• Set Primary Process Type = Integrating
• Choose controller structure 3 (I action on error, PD action on PV (= 0 and = 0))
• Make setpoint change from 50% to 60%
[File Name or Event]Emerson Confidential27-Jun-01, Slide 16 Slide 16
Other Control Loop OpportunitiesOther Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup Time
Other Control Loop OpportunitiesOther Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup Time
Output Lead-Lag – A lead-lag on the controller output or in the digital positioner can kick the signal
though the valve deadband and sticktion, get past split range points, and make faster transitions from heating to cooling and vice versa.
– A lead-lag can potentially provide a faster setpoint response with less overshoot when analyzers are used for closed loop control of integrating processes When combined with the enhanced PID algorithm (PIDPlus) described in:
• White paper http://www.modelingandcontrol.com/DeltaV-v11-PID-Enhancements-for-Wireless.pdf
Deadtime Compensation– The simple addition of a delay block with the deadtime set equal to the total loop
deadtime to the external reset signal for the positive feedback implementation of integral action described in Deminar #3 for the dynamic reset limit option http://www.screencast.com/users/JimCahill/folders/Public/media/f093eca1-958f-4d9c-96b7-9229e4a6b5ba .
– The controller reset time can be significantly reduced and the controller gain increased if the delay block deadtime is equal or slightly less than the process deadtime as studied in Advanced Application Note 3 http://www.modelingandcontrol.com/repository/AdvancedApplicationNote003.pdf
[File Name or Event]Emerson Confidential27-Jun-01, Slide 17 Slide 17
Other Control Loop OpportunitiesOther Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup Time
Other Control Loop OpportunitiesOther Control Loop Opportunitiesto Reduce Fed-Batch and Startup Timeto Reduce Fed-Batch and Startup Time
Feed Maximization– Model Predictive Control described in Application Note 1
http://www.modelingandcontrol.com/repository/AdvancedApplicationNote001.pdf – Override control (next slide) is used to maximize feeds to limits of operating
constraints via valve position control (e.g. maximum vent, overhead condenser, or jacket valve position with sufficient sensitivity per installed characteristic).
– Alternatively, the limiting valve can be set wide open and the feeds throttled for temperature or pressure control. For pressure control of gaseous reactants, this strategy can be quite effective.
– For temperature control of liquid reactants, the user needs to confirm that inverse response from the addition of cold reactants to an exothermic reactor and the lag from the concentration response does not cause temperature control problems.
– All of these methods require tuning and may not be particularly adept at dealing with fast disturbances unless some feedforward is added. Fortunately the prevalent disturbance that is a feed concentration change is often slow enough due to raw material storage volume to be corrected by temperature feedback.
Profile Control– If you have a have batch measurement that should increase to a maximum at the
batch end point (e.g. maximum reaction temperature or product concentration), the slope of the batch profile of this measurement can be maximized to reduce batch cycle time. For application examples checkout “Direct Temperature Rate of Change Control Improves Reactor Yield” in a Funny Thing Happened on the Way to the Control Room http://www.modelingandcontrol.com/FunnyThing/ and the Control magazine article “Unlocking the Secret Profiles of Batch Reactors” http://www.controlglobal.com/articles/2008/230.html .
04/13/23 18
feed A
feed B
coolantmakeup
CAS
ratio
CAS
Example of Advanced Regulatory ControlExample of Advanced Regulatory Control(reduced batch cycle time by 25%)(reduced batch cycle time by 25%)
reactor
vent
product
maximum productionrate
condenser
CTW
PT
PC-1
TT
TT
TC-2
TC-1
FC-1
FT
FT
FC-2
<
TC-3
RC-1
TT
ZC-1
ZC-2CAS
CAS
CAS
ZC-3 ZC-4<
Override Control
override control
ZC-1, ZC-3, and ZC-4 work to keep their respective
control valves at a max throttle position with good
sensitivity and room for loop to maneuver. ZC-2
will raise TC-1 SP if FC-1 feed rate is maxed out
[File Name or Event]Emerson Confidential27-Jun-01, Slide 19 Slide 19
Sequence Opportunities Sequence Opportunities to Reduce Pure-Batch and Startup Timeto Reduce Pure-Batch and Startup Time
Sequence Opportunities Sequence Opportunities to Reduce Pure-Batch and Startup Timeto Reduce Pure-Batch and Startup Time
Reduce wait times, operator attention requests, and manual actions by automation.
Reduce excess hold times (e.g. heat release can confirm reaction start/end). Improve charge times and accuracy by better sensor design (e.g. mass flow
meters and valve location (e.g. minimize dribble time and holdup). Minimize acquire time by improved prioritization of users (e.g. unit operation
with biggest effect on production rate gets access to feeds and utilities). Reduce failure expression activation by better instruments, redundancy and
signal selection, and more realistic expectations of instrument performance. Improve failure expression recovery by configuration and displays. Eliminate steps by simultaneous actions (e.g. heat-up and pressurization). Increase feed and heat transfer rate by an increase in pump impeller size. Minimize non constrained processing time by all out run, cutoff, and coast. Minimize processing time by better end point detection (inferential
measurements by neural networks and online or at-line analyzers). Mid batch correction based on adapted online virtual plant model or batch
analytics projection to latent structures (PLS) and first principle relationships.
[File Name or Event]Emerson Confidential27-Jun-01, Slide 20 Slide 20
Demo of Effect of PID Structure 1Demo of Effect of PID Structure 1on Setpoint Responseon Setpoint Response
Demo of Effect of PID Structure 1Demo of Effect of PID Structure 1on Setpoint Responseon Setpoint Response
Objective – Show faster setpoint response from addition of kick from proportional mode and bump derivative mode
Activities:– For Single Integrating Loop:
• Look at setpoint response for structure 3
• Choose controller structure 1 (PID action on error (= 1 and = 1))
• Make setpoint change from 60% to 50%
[File Name or Event]Emerson Confidential27-Jun-01, Slide 21 Slide 21
Identified Responses for Identified Responses for Batch Profile ControlBatch Profile Control
[File Name or Event]Emerson Confidential27-Jun-01, Slide 22 Slide 22
Product Formation Rate
Biomass Growth rate
Substrate
Dissolved Oxygen
Model Predictive Control (MPC) of Model Predictive Control (MPC) of Growth Rate and Product Formation RateGrowth Rate and Product Formation Rate
[File Name or Event]Emerson Confidential27-Jun-01, Slide 23 Slide 23
Demo of Effect of SP FeedforwardDemo of Effect of SP Feedforwardon Setpoint Responseon Setpoint Response
Demo of Effect of SP FeedforwardDemo of Effect of SP Feedforwardon Setpoint Responseon Setpoint Response
Objective – Show how reduce batch cycle time by use of setpoint feedforward
Activities:– For Single Integrating Loop:
• Look at setpoint response for structure 1
• Set SP FF Gain = 2
• Make setpoint change from 50% to 60%
[File Name or Event]Emerson Confidential27-Jun-01, Slide 24 Slide 24
Batch Basic Fed-Batch APC Fed-BatchBatch
Inoculation Inoculation
Dissolved Oxygen (AT6-2)
pH (AT6-1)
Estimated Substrate Concentration (AT6-4)
Estimated Biomass Concentration (AT6-5)
Estimated Product Concentration (AT6-6)
Estimated Net Production Rate (AY6-12)
Estimated Biomass Growth Rate (AY6-11)
MPC in Auto
Model Predictive Control (MPC) Model Predictive Control (MPC) Reduces Batch Cycle TimeReduces Batch Cycle Time
[File Name or Event]Emerson Confidential27-Jun-01, Slide 25 Slide 25
Model Predictive Control (MPC) Model Predictive Control (MPC) Improves Batch PredictionsImproves Batch Predictions
[File Name or Event]Emerson Confidential27-Jun-01, Slide 26 Slide 26
Demo of Effect of Bang-Bang ControlDemo of Effect of Bang-Bang Controlon Setpoint Responseon Setpoint Response
Demo of Effect of Bang-Bang ControlDemo of Effect of Bang-Bang Controlon Setpoint Responseon Setpoint Response
Objective – Show how to reduce batch and startup time by a full throttle setpoint response (bang-bang control)
Activities:– For Single Integrating Loop:
• Look at setpoint response for setpoint feedforward
• Set SP FF Gain = 0
• Set Bang-Bang Bias = 4%
• Make setpoint change from 60% to 50%
[File Name or Event]Emerson Confidential27-Jun-01, Slide 27 Slide 27
Structure 3Rise Time = 8.5 min
Settling Time = 8.5 minOvershoot = 0%
Structure 1Rise Time = 1.6 min
Settling Time = 7.5 minOvershoot = 1.7%
Structure 1 + SP FFRise Time = 1.2 min
Settling Time = 6.5 minOvershoot = 1.3%
Structure 1 + Bang-BangRise Time = 0.5 min
Settling Time = 0.5 minOvershoot = 0.2%
Summary of Demo ResultsSummary of Demo ResultsSummary of Demo ResultsSummary of Demo Results
[File Name or Event]Emerson Confidential27-Jun-01, Slide 28 Slide 28
Help Us Improve These Deminars!Help Us Improve These Deminars!Help Us Improve These Deminars!Help Us Improve These Deminars!
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[File Name or Event]Emerson Confidential27-Jun-01, Slide 29 Slide 29
Join Us Aug 25, Wednesday Join Us Aug 25, Wednesday 10:00 am 10:00 am CDTCDTJoin Us Aug 25, Wednesday Join Us Aug 25, Wednesday 10:00 am 10:00 am CDTCDT
PID Control of Runaway Processes PID Control of Runaway Processes (How to Improve the Performance of Exothermic Reactor Temperature Loops)
Look for a recording of Today’s Deminar later Look for a recording of Today’s Deminar later this week at:this week at: