运用PID控制英文文献Word文件下载.docx
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运用PID控制英文文献Word文件下载.docx
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Woodward1992
AllRightsReserved
ApplicationNote83402PIDControl
Woodward1
Contents
CHAPTER1.INTRODUCTION.........................................................................2
ProcessControlLoop.............................................................................................2
AutomaticControl...................................................................................................3
ControlLoop...........................................................................................................4
ControlModes........................................................................................................4
ControlModes(CarAnalogy).................................................................................5
ProportionalControl................................................................................................5
Integral(Reset).......................................................................................................5
Derivative(PreactandRateTime).........................................................................5
ControlResponses.................................................................................................6
CHAPTER2.SINGLE-MODECONTROL.........................................................7
On-OffControl........................................................................................................7
ProportionalResponse...........................................................................................9
ProportionalGain(EffectofSettings).....................................................................9
Chapter2Summary.............................................................................................10
Chapter2ReviewQuestions................................................................................10
CHAPTER3.INTEGRALANDDERIVATIVECONTROL....................................11
Proportional+Integral(OpenLoop).....................................................................11
Integral..................................................................................................................12
Proportional+Integral(ClosedLoop)..................................................................13
Integral(EffectsofSettings).................................................................................14
DerivativeResponse............................................................................................15
Derivative(Minutes)..............................................................................................16
Proportional+Derivative(ClosedLoop)..............................................................17
Derivative(EffectsofSettings).............................................................................18
Proportional+Integral+Derivative(ClosedLoop)..............................................19
Chapter3Summary.............................................................................................19
Chapter3Review.................................................................................................20
CHAPTER4.TUNINGGUIDELINES..............................................................22
ControllerTuningMethodSample........................................................................24
ControllerFieldTuningGeneral...........................................................................25
ControllerFieldTuningProcedure.......................................................................27
PIDControlApplicationNote83402
2Woodward
Chapter1.
Introduction
ProcessControlLoop
Withthisblockdiagramofacontrolloop,thefollowingcanbeshown:
Thedashessurroundingthemeasurementtransmitter,thecontrolstation,and
thecontrollerindicatethe"
local"
controlstationsinceallpartsarewithinone
case.
Thedashessurroundingthecontrolstationandcontrolleronlyindicatethe
"
remote"
controlstation.
Thecontrollerinthiscasemaybemountedoneofthreeways:
onthecontrolstation
behindthecontrolpanelonarackwithothercontrollers
inthefieldonornearthecontrolvalve.
Itmayalsobeanintegralpartofthecontrolstationastheoneusedinthetraining
setup.
Bothtypesofcontrolstationswillhavesomewayofindicating(orrecording)the
processvariable,somemeansforadjustingthedesiredsetpoint,andameansfor
readingthecontrolleroutputtothecontrolvalve.The"
controlstationmayor
maynothaveameansfor"
manually"
controllingthecontrolvalve.The"
willalwayshavethisfacility.The"
controlstationrequiresfrequentvisitation
todeterminequalityofcontrol.The"
stationiscentrallylocated,therefore
reducingtraveltimeandallowingside-by-sidecontrolqualityscanning.
Woodward3
Thefunctionofeachblockofthediagramisasfollows:
1.Measurementtransmitter—measurestheprocessvariable(temperature,
pressure,level,flow,oranalysis)andconvertsthemeasurementtounits
usefultothecontroller(psig,kPa,etc)orsomeelectronicvaluesuchas4–20
mA.
2.Thecontrolstationprovidesfacilityforsettingthedesiredcontrolpoint,
readingthevalueofthemeasurement,transferringtheoperationfrommanual
toautomaticorautomatictomanual,andallowsmanualloadingofthecontrol
valve.
3.Thecontrollertakesthesetpointvalueofthecontrolstation,comparesits
valuetothemeasurementandreactstothedifferenceaccordingtothevalues
setoneachresponse,proportional,resetandderivative.
4.Theoutputsignalfromthecontrollerpositionsthecontrolvalve.
5.Theprocesschangesresultingfromthevalvechangesarefeltbythe
measurementandtheprocedurecontinues.
AutomaticControl
Thischartisasimplifiedformofthepreviouschart.Therearethreethingsthattake
place:
measurement
decision
action
Measurement,ofcourse,istheprocessvariabletobecontrolled.
Thedecisionisthecontroller.
Theactionisthecontrolvalve,sometimescalledthefinalelement.
Notethatthearrowsflowcontinuouslyasdoesthefunctionofanyclosedloop
controlsystem.Allsectionsofthecontrolsystemarecontinuouslyconnected,even
thoughactiondoesnottakeplaceunlessachangetakesplacethatresultsinthe
processvariablemeasureddeviatingfromthesetpoint(desiredcontrolpoint).
4Woodward
Tobreaktheconnectionbetweenanysectionoftheloopwouldresultinanopen
loopconfiguration.Ofcourse,theprocesswillthennotrespondtocontrolleraction.
However,aslaterchartswillshow,openloopconfigurationisauniquewayof
observingcontrolleractionsorresponsesonanindividualbasisandwithoutthe
interferingprocessresponse.
ControlLoop
Measurement(Transmitter)
1.Temperature
2.Pressure
3.Level
4.Flow
5.X-Analysis
Decision(Controller)
1.Setpointvs.measurement
2.Controllerresponse
Action(FinalElement)
1.Controlvalve
2.Pump
3.Rheostat
Controlloopcomponentsconsistofthoseshownontheabovechart.Asmentioned
earlier,threethingstakeplaceinaclosedloopcontrolsystem—Measurement,
Decision,Action,wheneverthesystemisinautomatic.Themeasurementsection
isconnecteddirectlytotheprocessandtransmitsthevariabletobecontrolledto
thecontrolstation,usuallysomedistanceaway.Thecontrolstation,which
technicallyincludesthecontroller,allowscomparisonbetweenthedesiredcontrol
point(setpoint)andthemeasuredcontrolpoint.Theamountofthedeviation,the
rateofthedeviationandthedurationofthedeviationallpredictcontrollerresponse
accordingtothecontroller'
sgain,derivativeandresetsettings.
Theactionissimplytheresultofthecontrolleroutput.Itmaybesomethingother
thanacontrolvalve.
ControlModes
On-OffOr(Deadband)
Proportionalor(Prop_Gn)
Integralor(Int_Gn)
Derivativeor(S_D_R)
Asmentionedearlier,modesofcontrolrefertothevarioustypesofcontrol
available.Alsoitmustberememberedthatthetypeofcontrolshouldmatchthe
process.Forexample,on-offcontrolisquiteadequateforhomeheatingsystems,
butwouldbeveryunsatisfactoryinmostpetroleum/chemicalapplicationsbecause
ofitscycliccharacteristic.
Proportionalcontroleliminatesthecycliccharacteristicsoftheon-offmode.
IntegralandDerivativearerefinementsofandworkinconjunctionwithproportional
control.Specialstudiesofeachfollow.
Woodward5
ControlModes(CarAnalogy)
ON-OFF—Onespeedwindshieldwiperinlightrain.
Onewaytodescribetermsnormallyunfamiliaristodrawananalogytosomething
whichisfamiliar.
TheanalogyhereforOn-Offcontrolisturningthewindshieldwiper"
on"
then"
off"
.
Itsspeedisnotchanged.Itissimplyturned"
foronewipe,thenturnedoff.
A
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