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Interesting and UsefulFeatures of the DeltaV PIDControllerJames Beall – Emerson Process Management
Introduction Provide additional information on useful features ofthe DeltaV PID and related function blocks. Discuss some common PID function blockparameters where the default values can cause poorcontrol. Provide examples of the use of these features. Note – “BOL” is DeltaV Books on Line (theembedded, electronic DeltaV documentation)
Topics PID FormPID StructureIntegral Dead BandSP Filter/Rate ofChangeSP LimitsCascade Features Gain SchedulerNon-linear GainOutputCharacterization (toValve)Anti-Reset WindupLimitsQuestions
PID “Form” Three Common PID Forms– Parallel Form– Standard, aka ISA Form,– Series, aka Classical Form. DeltaV has Choices– Standard (default)– Series
PID “Form” - PID Function Block DeltaV default is “Standard”Note that if you choose “Nonlinear Gain” inFRSPID OPTS then the FORM becomes“Standard” – More on this laterFORMNoneSelects equation form (series orstandard). If Use Nonlinear GainModification is selected inFRSIPID OPTS, the formautomatically becomes standard,regardless of the configuredselection of FORM.
Standard Form of the PID EquationError SP - PV1TR sIOUTPUT P I DPSP PVKC -TDSDPROCESS
Classical Form of the PID EquationDTDSErrorOUTPUTPSP -KC 1TR sIPVPROCESS
PID “Form” Choice Prior system experiencePersonal Preference for Standard or SeriesSeries is identical to Standard form ifDerivative action is NOT usedCan impact conversion of tuning constantsfrom previous control system
Convert Series (Classical) to Standard Series is identical to Standard form if Derivativeaction is NOT usedTR should be time/rep & same time units as TDBe sure to convert units after form conversionKC Standard KC Series *TR Standard TR SeriesTR SeriesTDTSeriesClassical D Classical*TR SeriesClassical0 TTDDClassicalSeries0TD Standard TR Series* DTSeriesClassical* TD Classical0( TR Series) )Classical TDTSeriesD Classical
PID Function Block “Structure” ParameterUsed most.Default
PID Function Block “Structure” Parameter SP Change on Reactor feed tank level: PI onerror, D on PVController Output – Flow to reactorSP
PID Function Block “Structure” Parameter SP Change on Reactor feed tank level: I onerror, PD on PVController Output – Flow to reactorSP
PID Structure – 2 Degrees of Freedom BETA - determines the degree of proportional actionthat will be applied to SP changes.– Range 0-1– BETA 0 means no proportional action is applied to SP change.– BETA 1 means full proportional action is applied to SP change. GAMMA - determines the degree of derivativeaction that will be applied to SP changes.– Range 0-1– GAMMA 0 means no derivative action applied to SP change.– GAMMA 1 means full derivative action is applied to SP change.
PID Structure – 2 Degrees of Freedom
Integral Dead Band IDEADBAND - When the error gets withinIDEADBAND, the integral action stops. Theproportional and derivative action continue.Same Engineering Units as PV ScaleMay be used to reduce the movement of thecontroller output when the error is less thanthe “IDEADBAND”. For example on a levelcontroller that feeds the downstream unit.
Set Points Filter/Rate of Change SP FTIME - Time constant (seconds) of the first order SPfilter. The Set Point Filter applies in AUTO, CAS andRCAS (not specified in BOL).SP RATE DN - Ramp rate at which downward setpointchanges are acted on in Auto mode, in PV units persecond. If the ramp rate is set to 0.0, then the setpoint isused immediately. For control blocks, rate limiting appliesonly in Auto (not CAS or RCAS).SP RATE UP - Ramp rate at which upward setpointchanges are acted on in Auto mode, in PV units persecond. If the ramp rate is set to 0.0, then the setpoint isused immediately. For control blocks, rate limiting appliesonly in Auto (not CAS or RCAS).
Set Point Limits SP HI LIM- The highest SP value (EU’s)allowed.SP LO LIM - The lowest SP value (EU’s)allowed.Control Options – allow you to specify if SPLimits to be obeyed in “CAS and RCAS”Can use “Output Limits” of Master loop incascade pair to limit SP to Slave loop ONLYin CAS and RCAS
Cascade FeaturesColumnTray 6Master Loop aka Primary LoopLC3-2LT3-2RSPSlave Loop aka Secondary LoopFC3-5FT3-5Bottoms
Cascade Features Mode tracking and bumpless transfers areautomatically provided through the BKCALfeatureLimited conditions in the Slave loop are takencare of through the BKCAL featurePrevent reset windup with external reset byselecting “Dynamic Reset Limit” inFRSIPID OPTS on the Master loop“Use PV for BKCAL OUT” in CONTROL OPTSshould be selected on Slave loop for use withDynamic Reset Limit in Master
Enabling PID External Reset Utilized most oftenin the primary loopof a cascadeAutomaticallycompensates forpoor secondary loopresponse
Gain Scheduler Proves up to 3 regions of different PID tuningparameters based on a selected state variable(output, PV, error, production rate, etc.)Provides a smooth transition between regionsCreate PID module using Module Templates:Analog Control/PID GAINSCHEDOR, add function to existing PID module– Expose Gain, Reset and Rate parameters on PIDfunction block– Copy all function blocks from template except thePID FB and link as needed.
Gain SchedulerModule Templates: Analog Control/PID GAINSCHED
Gain Scheduler
Gain Scheduler – Detail Display
FRSIPID OPTS: Non-linear Gain Modifies the proportionalGain as a function of theerror (PV-SP)Can be used to makethe tuning moreaggressive as the PV isfarther from the set pointCan create the “errorsquared” PID function
FRSIPID OPTS: Non-linear GainThe PID “Gain” is multiplied by “KNL” which has a value between 0and 1 as a function of the error (SP-PV).KnlKnl 1Knl NL MINMODe NL TBANDNL GAPNL HYSTPV-SP
FRSIPID OPTS: Non-linear Gain The PID “Gain” is multiplied by “KNL” which has avalue between 0 and 1 as a function of the errorI typically set NL HYST 0Be aware that using this feature on an integratingprocess, like levels, can cause oscillations at thereduced gain. For these applications, the reset timeshould be based on “Gain*MINMOD” which will resultin a larger reset time to prevent oscillations.For this affect on integrating processes, considerusing the Gain Scheduler
FRSIPID OPTS: Non-linear Gain “Error2” “Error squared” PID function – error*abs(error)Proportional error*abs(error)*gain error* (abs(error)*gain)Proportional error*(Modified Gain)Non-linear GainModified Gain abs(error)*GainSettings for E2ModifiedGainErrorActivate NL GainNL MINMOD 0NL GAP 0NL TBAND 100NL HYST 0
Output Characterization to Valve Use a “Signal Characterizer” function block tochange valve characteristics– Note the best solution is to change valve trim toproper characteristicSGCR Characterizes IN 1 to OUT 1 Reverse Char. IN 2 to OUT 2
Output Characterization to Valve See Books On Line for rules forthe X and Y curvesSet “SWAP 2” TRUE toprovide a “reverse”characterization for the BKCALsignal (The answer in V9.3 andlater is “Change X by Y axis onIN-2”.)BOL: The SWAP 2 parameter swaps the X and Y axes used forOUT 2. When the SWAP 2 parameter is True, IN 2 references theCURVE Y values and OUT 2 references the CURVE X values. Inaddition, the IN 2 units change to Y UNITS and the OUT 2 unitschange to X UNITS.
Anti-Reset Windup Limits Improves process recovery from saturatedconditionsOn recovery from a saturated condition, whenthe ARW HI LIM and ARW LO LIM are setinside the OUT limits, the reset time willautomatically be decreased (faster) by 16Xuntil the OUT parameter comes back withinthe the ARW limits or the control parameterreaches setpoint.
Setting ARW limitsPVSPOUTARW LO LIMOUT LO LIM
Setting ARW Limits – Important!!!!! ARW limits are in Engineering Unitsof the OUT SCALE. The default is0-100. If the OUT SCALE is otherthan 0-100, be sure to initially setARW limits to the OUT SCALElimits. For example, for the master loop ofcascaded loops, the OUT SCALE is0-25,000 lbs/hr. Set ARW HI LIM 25,000 and ARW LO LIM 0.
Business Results Achieved These features can be used to significantly improvedthe performance of PID controlThe default ARW limits of 0-100 is a commonproblems for the master loop in a cascadearrangement. Correcting the ARW limits improvescontrol.These features can be used to customize theresponse of the PID controller to meet processrequirements“Difficult” process dynamics can be handledBottom line – Better control performance
Summary DeltaV has many useful control features Watch out for default parameters (ARW limits) thatdon’t match your application Better control performance Questions
Where To Get More Information Emerson Process Management Education Services– DeltaV Advanced ControlCourse: # 7201 - CEUs: 3.2– DeltaV Operate Implementation ICourse: # 7009 - CEUs: 3.2– EnTech - Process Dynamics, Control and TuningCourse: # 9030 CEUs: 2.8 Emerson Process Management, AdvancedAutomation nsulting/advancedautomation/index.asp [email protected] , 903-235-7935
About the Presenter James Beall is a Principal Process Control Consultant withEmerson Process Management. He has over 26 yearsexperience in process control, including 7 years with Emersonand 19 years with Eastman Chemical Company. He graduatedfrom Texas A&M University with Bachelor of Science degree inElectrical Engineering. His areas of expertise include processinstrumentation, control strategy analysis and design, controloptimization, DCS configuration and maintenance, control valveperformance testing and Advanced Process Control. James is acontributing author to Process/Industrial Instruments andControl Handbook (5th Edition, G.K. McMillan, McGraw-Hill,New York, 1999. He is a member of AIChE and is currently thechairman of ISA Subcommittee 75.25, Control ValvePerformance Testing.
Introduction Provide additional information on useful features of the DeltaV PID and related function blocks. Discuss some common PID function block parameters where the default values can cause poor control. Provide examples of the use of these features. Note –“BOL” is DeltaV Books on Line (the embedded, electronic DeltaV documentation)File Size: 956KB
