Basic Process Control
Basic Control PrinciplesInflowSupplyllllllLevel(Controlled Variable)PumpOverflow
Open vs Closed Loop!Closed loop!!Automatic controlOpen Loop!!Manual controlPerson takes the place of the controller
Feedback ControlDisturbancesControllerSet PointComparatorErrorAmplifier(SP - M)ManipulatedVariableProcess (Tank)Output(ControlledVariable - Level)MeasurementSignalProcessSensor
Feedback vs. Feedforward!Feedback!!Control action after an error existsFeedforward!Reacting to the disturbance before theerror occurs
Typical ON/OFF Control SystemV1SPlllQoutQinlllL2L1P1P1 closes @ L1P1 opens @ L2InflowElectrically OperatedSolenoid valveSolenoidPower Supply
Typical ON/OFF ResponseL2SPtimeL1Periodic Time
Proportional Control
Level Control of Open TankV1SPlllQoutQinlllA/CLT20 - 100 kPa
Simple Proportional SystemInflowValvePivotllFloatlllOutflow
Open Tank ControlA/O20 - 100 kPaQinSPLICLTQout
Controller ActionA/CSPlllQoutQinlllDirect20 - 100 kPaLICLTA/OSPReverselllQoutQinlll20 - 100 kPaLICLT
Proportional ControlSetpoint Error-k e BiasMeasurementm k(SP-M) biasOutput
Proportional Band and GainProportional Band – the input change required tochange the output 100% outputgain input100%gain PB
Narrow, Wide, High & LowInWide PB – Low GainNarrow PB – High GainOut
Proportional Control ResponseCurveNew mass balanceoccurs hereLoss in VolumeOutflowInflowInput/Outputt0timet1tLevel originallyat setpointOffsetLevelt0t1timeNew levelbelow setpoint
Proportional Response withNarrower PBNew mass balanceoccurs hereLoss in VolumeOutflowInput/OutputInflowt0timet1tLevel originallyat setpointLevelOffsett0New levelbelow setpointt1time
Load ChangeResponse Versus PB, ProportionalControl OnlySPStep Disturbancetime"Wide" PBSystem ResponseOffsetSPSP"Moderate" PBOffset"Narrow" PBtime
System Response¼ Decay Response CurveAA/16A/4time
For You To Do!!Read pp. 89-105Answer Questions pp. 121-122, #1-19
Reset or Integral
Response Curve: ProportionalControl OnlySystem ResponseStep DisturbancetimeSPOffset
Additional Control Signal RestoresProcess to SetpointInitial mass balanceFinal mass balanceOutflowReset ActionInflowSetpointOffsetRemovedtime
Integral Action1edt TRSetpoint Error-Measurementk e Bias 1m ke edt bias TROutput
Units!Minutes per repeat!!!MPRThe length of time that it will take theintegrator to add an amount equal to theproportional responseRepeats per minute!!RPMThe number of times the proportionalresponse is repeated in one minute
Proportional Plus Reset, Open LoopResponseerrorControl SignaleFa}stseeRtNokeProportionalResponseR eslarmetSlow Resettime
A problemOutput initially 50%, Gain 2, reset 2 minutes per repeatA direct acting controller control is subjected to a sustainederror of 5%What is the output after 4 minutes?Proportional Response ke 2x5 10%Integral Action- in 4 minutes the control will go through 2 repeats.Integral action 2 x 10 20%Total output change is proportional integral 30%
A Couple More Things!!Reset WindupInstability because of lag
For You to Do!!Read over text pp. 89 –110Answer questions pp. 121-122, 1-24
Rate or Derivative
OutputInputProportional and Derivative – OpenLoop PressureDerivative ceases aserror stops changingProportionalActionDerivativetime
Derivative Control1edt TRSetpoint Errork e- Output BiasMeasurementTDdedt 1 de biasm ke edt kTDdt TR
Simple Flow Control Systeml ll FTA/CFC
ProcessThe open Loop Response of Proportional PlusDerivative (PD) Action to Rapidly ChangingError SignalsControlSignal%BACt0t1 t2timeProportional actionA-BRate action due to cessation of increase in eRateRate actionactionB -CA-BControl signal at end of excursionRate action due to cessation of increase in eProportionalaction B - Ct0t1 t2time
Large System Under Proportional andProportional Plus Derivative ControlControl SignalLoadDisturbanceAppliedProp. DerivativeProp. OnlySetpointLeveltime
Multiple Control Modes!!!!Virtually all controls have a proportionalresponseIntegral and derivative are added toimprove performanceMajority have proportional and integralSome, typically heat exchangers havederivative added
Open Tank Level Control WithValve In InflowA/OLICSPLTlllQiQolll
Typical Flow Control Loopl l FTA/OFICSP
Pressure Control – ConstantBleedSPPICFeedPTPressure VesselA/CPressureBleed
Split Ranged Feed and BleedPressure ControlSPPICPTA/OFeedPressure VesselA/CBleed
Representative Hot Bleed/Cold ServiceWater Heat ExchangerHot BleedColdA/CTTCooled BleedTCSP
For You To Do!!Read pp. 106-120Answer Questions pp. 122-123, #20-38
Control Signal % Process. Large System Under Proportional and Proportional Plus Derivative Control time Control Signal Setpoint Level Load Disturbance Applied Prop. Derivative Prop. Only. Multiple Control Modes! Virtually all controls have a pr
IAEA - CANDU I & C SNERDI, Shanghai Lesson 10: Overall Unit Control Module 1: Boiler Pressure Control page 10 - 1 - 5 Response to Reactor Trip Under these conditions heat input to the boilers has been reduced rapidly towards zero. The turbine output must also be quickly reduced to avoid a gross energy mismatch which could drastically reduce the pressure and temperature of the HTS.
Maintenance and maintenance support (IEC 60300-3-14) Reliability Centred Maintenance (IEC 60300-3-11) * Candu Energy Inc. is neither involved nor a sponsor of the work described in this paper. CANDU is a
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