基于PLC的锅炉温度控制系统 英文材料

PAGEPAGE1基于PLC的锅炉温度控制系统英文材料泡芙小工坊PLCBASEDBOILERTEMPERATURECONTROLLERControllingappliancesfromourPCisquiteinterestingandconvenient.InthisprojectthesimplecircuitalongwiththesoftwareisusedtointerfacethePCwiththeElectroniccircuit.ThisprojectconsistsofthreemodulescalledPLCcontrolpanel,boilersensorunitanddisplayunit.TheGates(And,Or,Notetc)andtheInputvariablesaresetinthesystem.ThecorrespondingsignalistransmittedthroughparallelportandthePLCkitreceivesthesignal.TheHighorLowInputaresetinthePLCkitbyusingswitches.ThecontroloperationsaredoneintheMicrocontrollerusingPLC(LadderLogic)Programming.TheoutputisderivedinthePLCkit.Byusingtheoutputonecancontrolanymachineormotor.Heatsensorsareconnectedattheboiler.Accordingtotheheatsensed,thesensorssendsignaltothePLCkit.AccordingtothevariablessetinthePLCkit,thekitsendssignaltothedisplaysection.Thustheusercanmonitortheheatleveloftheboileraswellashecancontroltheboiler.ThisprojectusesVisualBasicasdesigninglanguageandAssemblylanguageasMicrocontrollerlanguage.PIC16F73isusedasMicrocontroller.ControlofBoilerOperationusingPLC–SCADAK.GowriShankarAbstract––Thispaperoutlinesthevariousstagesofoperationinvolvedintheconversionofamanuallyoperatedboilertowardsafullyautomatedboiler.Overtheyearsthedemandforhighquality,greaterefficiencyandautomatedmachineshasincreasedinthisglobalisedworld.Theinitialphaseofthepaperfocusesonpassingtheinputstotheboileratarequiredtemperature,soastoconstantlymaintainaparticulartemperatureintheboiler.TheAirpreheaterandEconomizerhelpsinthisprocess.Andthepapermainlyfocusesonlevel,pressureandflowcontrolatthevariousstagesoftheboilerplant.Thusthetemperatureintheboilerisconstantlymonitoredandbroughttoaconstanttemperatureasrequiredbythepowerplant.TheautomationisfurtherenhancedbyconstantmonitoringusingSCADAscreenwhichisconnectedtothePLCbymeansofcommunicationcable.BymeansoftagvaluessettovariousvariableinSCADAtheentireprocessiscontrolledasrequired.Attheautomatedpowerplant,theboileriscontrolledbyVariableFrequencyDrive(VFD)toputinactiontherequiredprocessestobecarriedoutattheboiler.Thustheentirecycleiscarriedoutasapaperandatvariousstageseachphaseisdetailedout.Thispaperhasprovedtobeveryefficientpracticallyastheneedforautomationgrowsdaybyday.IndexTerms––Automation,PLC–SCADA,Boiler.I.INTRODUCTIONOvertheyearsthedemandforhighquality,greaterefficiencyandautomatedmachineshasincreasedintheindustrialsectorofpowerplants.Powerplantsrequirecontinuousmonitoringandinspectionatfrequentintervals.Therearepossibilitiesoferrorsatmeasuringandvariousstagesinvolvedwithhumanworkersandalsothelackoffewfeaturesofmicrocontrollers.Thusthispapertakesasincereattempttoexplaintheadvantagesthecompanieswillfacebyimplementingautomationintothem.Theboilercontrolwhichisthemostimportantpartofanypowerplant,anditsautomationisthepreciseeffortofthispaper.Inordertoautomateapowerplantandminimizehumanintervention,thereisaneedtodevelopaSCADA(SupervisoryControlandDataAcquisition)systemthatmonitorstheplantandhelpsreducetheerrorscausedbyhumans.WhiletheSCADAisusedtomonitorthesystem,PLC(ProgrammableLogicController)isalsousedfortheinternalstorageofinstructionfortheimplementingfunctionsuchaslogic,sequencing,timing,countingandarithmetictocontrolthroughdigitaloranaloginput/outputmodulesvarioustypesofmachinesprocesses.Systemsareusedtomonitorandcontrolaplantorequipmentinindustriessuchastelecommunications,waterandwastecontrol,energy,oilandgasrefiningandtransportation.II.DRAWBACKOFCONVENTIONALSYSTEMConventionalequipmentsystemsarepronetoerrorsduetotheinvolvementofhumansinthedatacollectionandprocessingusingcomplicatedmathematicalexpressions.Thuswhatwerequireisasystemthatcollectsrawdata,processesitandpresentsitinvalueswhichcanbeverifiedandcomparedwiththestandardvalues.Inthecodingprocessofthisimplementationwithmicro-controller,itrequiresafastandefficientprocessingwhichontheotherpartdependsonthelengthandsub-routinesofthecodingprocess.ThusitprovidesarealchallengewithsystemsinvolvingIII.METHODSAllthevaluescanbefilledupbytheintroductionoftheautomationtechniqueintothepowerplants.Theautomationtechniqueinvolvingtheautomaticcontrolofalltheprocesseswhichincludesthemonitoringandinspectionneedsprovidesforaveryefficientsystem.Theautomationprocesshelpsthecompanyhavingthepowerplanttoreducetheamountoferrorsthatoccur,reductioninthehumanresources,increasedefficiency,andmostimportantlyverycosteffective.IV.CRITICALCONTROLPARAMETERSINBOILERA.LevelControlSteamDrumlevel,De-aeratorlevelandhotwelllevelB.PressureControlForcedraftpressure,Induceddraftpressure,Steamdrumpressure,Deaeratorpressure,Turbineinletsteampressure,balanceddraftpressureProceedingsoftheInternationalMultiConferenceofEngineersandComputerScientists2008VolIIIMECS2008,19-21March,2008,HongKongISBN:978-988-17012-1-3IMECS2008C.FlowControlAirflow,Steamflow,WaterflowD.TemperatureControlDeaeratortemperature,Steamdrumtemperature,Underbedboilertemperature,Turbineinletsteamtemperature,Fluegastemperature.V.AUTOMATIONDelegationofHumanControltotechnicalEquipmentaimedtowardsachieving.AdvantagesHigherproductivity,Superiorqualityofendproduct,Efficientusageofrawmaterialsandenergy,Improvedsafetyinworkingcondition.A.HistoryofControlandAutomationPLCELECTRICALCONTROLWITHLOGICGATESWITHLOGICGATESMANUALCONTROLManualControlInthis,theControlandAutomationaredonebyManualOperations.Drawbacks:HumanErrorssubsequentlyaffectqualityofendproduct.HardWiredLogicControlInthis,Contractorandrelaystogetherwithtimersandcounterswereusedinachievingdesiredlevelofautomation.Bulkyandcomplexwiring,Involveslotofreworktoimplementchangesincontrollogic,theworkcanbestartedonlywhenthetakesisfullydefinedandthisleadstolongerprojecttime.ElectronicsControlwithLogicGatesInthis,ContactorandRelaystogetherwithtimersandcounterswerereplacedwithlogicgatesandelectronictimersinthecontrolcircuits.AdvantagesReducedspacerequirements,energysaving,lessmaintenanceandhencegreaterreliability.TheMajorDrawbacksImplementationofchangesinthecontrollogicaswellasreducingtheprojectlead-timewasnotpossible.ProgrammableLogicControllerInthis,insteadofachievingdesiredcontrolandautomationthroughphysicalwiringofcontroldevices,itisachievingthroughprogramsaysoftware.AdvantagesReducedSpace,Energysaving,ModularReplacement,Easytroubleshooting,Errordiagnosticsprogrammer,Economical,Greaterlifeandreliability,TheCompatibilitiesofPLC’S,LogicControl,PIDcontrol,Operatorcontrol,Signalingandlisting,Coordinationandcommunication.B.HowPLCworksBasicsofaPLCfunctionarecontinualscanningofaprogram.Thescanningprocessinvolvesthreebasicsteps.Step1:TestinginputstatusFirstthePLCcheckseachofitsinputwithintentiontoseewhichonehasstatusonoroff.Inotherwordsitcheckswhetheraswitchorasensoretc.,isactivatedornot.Theinformationthattheprocessorthusobtainsthroughthisstepisstoredinmemoryinordertobeusedinthefollowingsteps.Step2:ProgrammingexecutionHereaPLCexecutesaprograminstructionbyinstructionbasedontheprogramandbasedonthestatusoftheinputhasobtainedintheprecedingstep,andappropriateactionistaken.Theactionmightbeactivationofcertainoutputsandtheresultscanbeputoffandstoredinmemorytoberetrievedlaterinthefollowingsteps.Step3:CheckingandCorrectionofoutputstatusFinally,aPLCchecksupoutputsignalsandadjustithasneeded.Changesareperformedbasedontheinputstatusthathadbeenreadduringthefirststepandbasedontheresultoftheprogramexecutioninsteptwo–followingexecutionofstepthreePLCreturnsabeginningofthecycleandcontinuallyrepeatsthesesteps.Scanningtime=Timeforperformingstep1+Timeforperformingstep2+Timeforperformingstep3.VI.ALLENBRADLEYPLCProgrammableLogicControllerorPLCisanintelligentsystemofmodules,whichwasintroducedinthecontrol,&instrumentationindustryforreplacingrelaybasedlogic[4].Overaperiodoftime,terI/Ohandlingcapabilitiesandmoreprogrammingelementshavebeenaddedalongwithimprovementincommunication.ProceedingsoftheInternationalMultiConferenceofEngineersandComputerScientists2008VolIIIMECS2008,19-21March,2008,HongKongISBN:978-988-17012-1-3IMECS2008PLCWorkingAtthebeginningofeachcycletheCPUbringsinallthefieldinputsignalsfromtheinputsignalsfromthemoduleandstoreintointernalmemoryasprocessofinputsignal.ThisinternalmemoryofCPUiscalledasprocessinputimage(PII).Userprogram(Application)willbeavailableinCPUprogrammemory.OncePIIisread,CPUpointermovesinladderprogramfromlefttorightandfromtoptobottom.CPUtakesstatusofinputfromPIIandprocessesalltherungsintheuserprogram.TheresultofuserprogramscanisstoredintheinternalmemoryofCPU.ThisinternalmemoryiscalledprocessoutputimageorPIQ.Attheendoftheprogramruni.e.,attheendofscanningcycle,theCPUtransfersthesignalstatesintheprocessimageoutputtotheoutputmoduleandfurthertothefieldcontrol.I/Odriver(SCADA)picksupPIIandPIQandtransferstheimagetodatabaseandthisimageiscalleddriverimage.ThisdriverimageavailableinSCADAdatabaseisusedforgraphicalviewofprocessmonitoringfromoperatorstation(OS)inthecentralcontrolroom.A.FeaturesofAllenBradleyPLCUsingAllenBradley1000PLCMicrologix1000PLChas20digitaloutputs.Therelationshipwithbitaddresstoinputandoutputdevicesisshowninthefigurebelow.C.ConnectingtothePLCOpenaSCADAapplicationCreateatagoftypeI/Odiscrete,selectthetypeasdiscreteSelectreadonlyifyoudon’twanttoforcevaluestoPLC.SelectingreadandwriteallowstotheSCADAtoreadandforcevaluestothePLC.Typeanaccessname.Theaccessnamecanvisualizedasagatewayforagroupofresources.MostofPLCdriverscommunicatewithSCADApackageusingDDE,DDErequiresthreeparametersnamelynameoftheDDEserver,topicnameanditemname.IncaseofreadinganumberofitemsfromaparticularPLCdriverapplicationnametopicnamearecommon,sothisapplicationnamethatisnameoftheDDEserverandTopicnamecombinetoformanaccessname.AccessnameisrequiredtobedefinedonlyoncethenotheritemsofdrivercanbeaccessedbyusingtheAccessnameanditemname.Thesedetailswillbeprovidedbythedrivervendorordeveloper.Clickok,theaccessnamewillbelistedfinallyclickdone,thentypetheitemname,clicksavetosavetheI/Otags.GotoruntimetocommunicatewithPLC.A.FlowchartTheoperationissummarizedasflowchartasbelowCONCLUSIONThemostimportantaspectofanypowerplantistheboilercontrol.Severaltechniquescanbeimplementedtocontroltheboilerinpowerplant.Themethodthathastobeusedreliesonvariedobjectiveslikesuperiorquality,increasedefficiency,highprofitandothersuchpointsdependinguponthepurposeofthecompanythatimpliesit.Withtheprimeobjectiveofcateringtothesenecessitiesandtheneedsoftheindustrialsector,significancehasbeengivenheretoautomation.Thispaperpresentedherehaskeptinmind,theceaselesschangesthatarerelentlesslytakingplaceinthecontemporaryscenariooftheindustrialsegment.Emphasishasbeengiventotheautomationprocessthatisnowrapidlytakingitsplaceinallthepowerplantsacrosstheglobe.ThePaperhasfurnisheditselftostudytheintegralpartsoftheentireprocessinvolved,theirimplementationandtheproblemsthatmayshowuphavealsobeengiventheirdueimportance.Thefutureworkdealswiththepurificationofwatertotheboilerandtheaircirculationfortheboilertoburnthefuelusingsameautomationtechnique.IntroductiontoTemperatureControllersHowdoTemperatureControllerswork?Toaccuratelycontrolprocesstemperaturewithoutextensiveoperatorinvolvement,atemperaturecontrolsystemreliesuponacontroller,whichacceptsatemperaturesensorsuchasathermocoupleorRTDasinput.Itcomparestheactualtemperaturetothedesiredcontroltemperature,orsetpoint,andprovidesanoutputtoacontrolelement.Thecontrollerisonepartoftheentirecontrolsystem,andthewholesystemshouldbeanalyzedinselectingthepropercontroller.Thefollowingitemsshouldbeconsideredwhenselectingacontroller:Typeofinputsensor(thermocouple,RTD)andtemperaturerangeTypeofoutputrequired(electromechanicalrelay,SSR,analogoutput)Controlalgorithmneeded(on/off,proportional,PID)Numberandtypeofoutputs(heat,cool,alarm,limit)WhatAretheDifferentTypesofControllers,andHowDoTheyWork?Therearethreebasictypesofcontrollers:on-off,proportionalandPID.Dependinguponthesystemtobecontrolled,theoperatorwillbeabletouseonetypeoranothertocontroltheprocess.On/OffControlAnon-offcontrolleristhesimplestformoftemperaturecontroldevice.Theoutputfromthedeviceiseitheronoroff,withnomiddlestate.Anon-offcontrollerwillswitchtheoutputonlywhenthetemperaturecrossesthesetpoint.Forheatingcontrol,theoutputisonwhenthetemperatureisbelowthesetpoint,andoffabovesetpoint.Sincethetemperaturecrossesthesetpointtochangetheoutputstate,theprocesstemperaturewillbecyclingcontinually,goingfrombelowsetpointtoabove,andbackbelow.Incaseswherethiscyclingoccursrapidly,andtopreventdamagetocontactorsandvalves,anon-offdifferential,or“hysteresis,〞isaddedtothecontrolleroperations.Thisdifferentialrequiresthatthetemperatureexceedsetpointbyacertainamountbeforetheoutputwillturnofforonagain.On-offdifferentialpreventstheoutputfrom“chattering〞ormakingfast,continualswitchesifthecyclingaboveandbelowthesetpointoccursveryrapidly.On-offcontrolisusuallyusedwhereaprecisecontrolisnotnecessary,insystemswhichcannothandlehavingtheenergyturnedonandofffrequently,wherethemassofthesystemissogreatthattemperatureschangeextremelyslowly,orforatemperaturealarm.Onespecialtypeofon-offcontrolusedforalarmisalimitcontroller.Thiscontrollerusesalatchingrelay,whichmustbemanuallyreset,andisusedtoshutdownaprocesswhenacertaintemperatureisreached.ProportionalControlProportionalcontrolsaredesignedtoeliminatethecyclingassociatedwithon-offcontrol.Aproportionalcontrollerdecreasestheaveragepowersuppliedtotheheaterasthetemperatureapproachessetpoint.Thishastheeffectofslowingdowntheheatersothatitwillnotovershootthesetpoint,butwillapproachthesetpointandmaintainastabletemperature.Thisproportioningactioncanbeaccomplishedbyturningtheoutputonandoffforshorttimeintervals.This"timeproportioning"variestheratioof“on〞timeto"off"timetocontrolthetemperature.Theproportioningactionoccurswithina“proportionalband〞aroundthesetpointtemperature.Outsidethisband,thecontrollerfunctionsasanon-offunit,withtheoutputeitherfullyon(belowtheband)orfullyoff(abovetheband).However,withintheband,theoutputisturnedonandoffintheratioofthemeasurementdifferencefromthesetpoint.Atthesetpoint(them