u simple Control law is strongly nonlinear If the corresponding time constants are large enough good control results at small errors can even be reached with discontinuous controllers and simple control elements Types of controllers Two position mod ID: 25882
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Lecture52013 Figure1:Responseonthecontrolaction[?]FeaturesoftheON-OFFControlGoodpointsMaxresponsetodeviations;reactsthesamewayondierentin-putsr=1;10;:::Simple,low-cost;outputcontactf0;1gDoesnotrequiretuning,suitableforallobjects.BadpointsPrecisionproblem;Frequentcyclingoftheactuatorleadstoprematurefailureduetome-chanicalwear;WasteofenergyheatedtoagraterTthannecessaryOn-ocontroliscommonforsimple,non-criticalapplications.athome:cooker,iron,refrigerator,etc.industry:compressors,fans(engine),heaters,valves,etc.Theidealon-ocontrollerFig.2isnotpractical:processesdisturbancesandelectricalinterfer-ence. ISS0065ControlInstrumentation2K.Vassiljeva Lecture52013 c u ON OFF H r c u ON H -directcharacteristicsparikarakteristikïðÿìîéðåãóëÿòîðKo0object:freezer-reversecharacteristicspoordkarakteristikîáðàòíûéðåãóëÿòîðKo&#x]TJ/;ø 9;&#x.962; Tf;&#x 10.;Ԗ ;� Td;&#x [00;0object:ironConsiderthreecontrolcaseswith1.integrating,2.inertial,3.andobjectwithadelay.Integratingobject(liquidlevelinthetank)W0=K01 s=1 T0sQ1�Q2=dV dt;V=R(Q1�Q2)dt=Sh h=1 sR(Q1�Q2)dtW0(s)=H(s) Q1(s)=K1 sQ2-output ow(0:::Q2max)-disturbance ISS0065ControlInstrumentation4K.Vassiljeva Lecture52013 Figure5:PumpscharacteristicsAperiodicorinertialobjectsW=K 1+Tos exponentialObjectswithdelayControlerrorT�H(ToisminifH=0).Errordependsondelayandtimeconstantratio =To =To 0.1 0.5 T=T 5% 20% )80C16C=64C:::96CStepcontrollerisnotsuitableforobjectswithdelay! ISS0065ControlInstrumentation6K.Vassiljeva 2013Lecture5 thermalobjectW=K 1+Tse�s RealizationofOn-OController1)byacontrollerPIDcontrollershaveON/OFFmode2)byawiringdiagramusingtwosensorsH1;H2H1=ONifh�h1H2=OFFifh�h2in ow electricaldiagram:relayKlaunchingthepump3)byaPLCalgorithm:pump=H1_ H2&pump1.2Threepositionmode/FloatingcontrolFloatingcontrolisavariationofOn/Ocontrolthatrequiresafastrespondingsensorandaslow-movingactuatorconnectedtothe nalcontrolleddevice(valveordamper).Floatingcontrolisnotacommoncontrolmode,butitisavailableinthemostmicroprocessor-basedcontrolsystems.Three-positioncontrollersprovidegoodqualityofcontrolforinertialobjectswithasmalldelay:controlofthemotors(rotationofdirection),heating/cooling/0.Floatingcontrolkeepsthecontrol K.Vassiljeva7ISS0065ControlInstrumentation 2013Lecture5 c du dt NB! 0 +Kf �Kf du=dt=f�Kf;0;Kfgu=Kft+u(0)Thecontrolprocesswith oatingcontrollerispresentedinFig.8. Figure8:Controlprocessusing3-pointcontroller1.3Multi-positioncontrollersMulti-positioncontrollerscanmanagemultipleloads,suchasgroupofheaters,fans,dampers,etc.Inthatcasecontrollerworksastheselector. c 0 1 4P 1 2P 3 4P P �3000rpm �1500rpm 0rpm 1500rpm 3000rpm rotationspeed heatingor Figure9:Staticcharacteristicofmulti-positioncontrolsystemcontrolleroutputu=fu1;u2;:::;u5g. K.Vassiljeva9ISS0065ControlInstrumentation