外文翻译--基于物理实验SimaticPLC运行的实时显示测量 英文版.pdf

IEEETRANSACTIONSONNUCLEARSCIENCE,VOL.51,NO.3,JUNE2004489MeasurementofRealTimeAspectsofSimatic®PLCOperationintheContextofPhysicsExperimentsHaraldKleines,JanosSarkadi,FrankSuxdorf,andKlausZwollAbstractToday,mostslowcontrolsystemsforphysicsexperimentsatForschungszentrumJülichareimplementedwithProgrammableLogicControllerPLCtechnologyandfieldbussystems.Inmanycases,evendeterministicresponseisrequiredfromthePLCs.ThisraisesthequestionabouttherealtimeperformancethatcanbeexpectedfromaPLC.ResponsetimemeasurementsofSimatic®PLCsmanufacturedbytheworldmarketleaderSiemensarepresented.InfluenceofprogramstructureandhardwareconfigurationonperformanceanddeterministicbehaviorofaPLCisdiscussed.I.PROGRAMMABLELOGICCONTROLLERSPLCSINEXPERIMENTCONTROLSYSTEMSTODAY,industrialautomationtechnologyiswellestablishedininfrastructuresystemsforphysicsexperiments,e.g.,inwaterorgassupplysystems.ThisleadstotheheavyuseofProgrammableLogicControllersPLCs,whichtypicallyaretheintelligentautomationstationsformingthecoreofindustrialsystems1.Mainreasonsincludelowpricesinducedbymassmarketrobustnesslongtermavailabilityandsupportfrommanufacturerprofessionalityconnectors,conformancetostandards,Beyondthescopeofpureinfrastructuresystems,PLCsareincreasinglybecomingcentralcomponentsofexperimentcontrolsystems,replacingVMEorPCbasedrealtimesystems2,3.ThisiscausedbythefollowingfeaturesofmodernPLCfamilies.HighdegreeofscalabilityModernPLCfamilieshaveawidespectrumofCPUtypes,thatisscalablenotonlywithregardtoperformance,butalsowithregardtofunctionalityandformfactor.Foroutdoororfaulttolerantapplicationsspecialversionsareavailable.ExtensibilityThemodulardesignofPLCsenablestheextensionwithawiderangeofdigitalandanalogI/Omodules.Additionally,integratedtechnologymodulesareavailablefordifferentapplicationareas,e.g.,steppermotorcontrollers,servomotorcontrollers,orPIDcontrollers.ExtensivecommunicationcapabilitiesModernPLCshaveatleastoneintegratedcommunicationportandcanbeextendedbyavarietyofcommunicationcontrollersManuscriptreceivedMay16,2003revisedOctober1,2003.TheauthorsarewithZentrallaborfürElektronik,ForschungszentrumJülich,D52425Jülich,Germanyemailh.kleinesfzjuelich.de.DigitalObjectIdentifier10.1109/TNS.2004.828504fordifferentfieldandprocessbussystems,thusenablingconnectionofotherindustrialdevices.AkeyissueistheextensionofacentralPLCsystemwithdecentralperipheryviaspecialfieldbussese.g.,PROFIBUSDP,thatallowsthetransparentconnectionofunintelligentI/Omodules.ThusaPLCprogramcanaccessthisdecentralperipheryinthesamewayascentralPLCperiphery.PowerfuldevelopmentenvironmentModernPLCfamiliescomewithahomogeneouscrossdevelopmentenvironment,thatsupportsallthemajorIEC1131programminglanguages4.Typically,representationsininstructionlistIL,functionblockdiagramFBDorladderdiagramLDcanbeswitcheddynamically.Thedevelopmenttoolsallowsemigraphicalhardwareconfiguration,offerstrongdebuggingmechanismsandallowincrementaldevelopmentbytheexchangeofblocksduringruntime.Today,inFZJuelich,allnewandadvancedexperimentcontrolsystemsareheavilyPLCbased3,asillustratedbythearchitectureofaneutronspectrometercontrolsystemshowninFig.1.BecausetheworldmarketleaderSiemensdominatestheEuropeanmarket,Simatic®S7PLCsareusedinFZJuelich,almostexclusively.ThemidrangeseriesS7300®ismostpopular.ThehighendseriesS7400®istargetedatapplicationswithextremeperformancerequirementsandsupportsalsomultiprocessorconfigurations.TheminiPLCseriesS7200®israrelyused,becauseitgotthenameS7bypuremarketingreasonsanditsprogrammingenvironmentisincompatibletotheotherS7devices.InsteadoftheS7200®,theIM151/CPUservesasaminiPLC.TheIM151/CPUisanintelligentcontrollerforthedecentralperipheryfamilyET200S®.AlsothedecentralperipherysystemsET200L®andET200M®areusedcommonlyinJülich.TheSoftPLCWinAC®hasonlybeentestedintheLab,sofar.TheresponsibleplanningofPLCbasedcontrolsystemsrequiresknowledgeontheirrealtimefeatures.WhatisthemagnitudeofPLCresponsetime,dependingonPLCtypeCandeadlinesbeguaranteedWhatprogrammingruleshavetobefollowedThepaperaddressestheseissuesbymeasurementsatdifferentPLCtypesoftheSimatic®S7family.ThestandardIEC1131definesacommonframeworkforPLCfunctionalityandprogramminglanguages4,whichallthemajorPLCmanufacturersconformto.ThusgeneralresultscanbegeneralizedalsototheirPLCfamilies.00189499/0420.00©2004IEEE490IEEETRANSACTIONSONNUCLEARSCIENCE,VOL.51,NO.3,JUNE2004Fig.1.ControlsystemarchitectureoftheneutronspectrometerKWS3.Fig.2.Blockcallinghierarchy.II.SIMATIC®S7PROGRAMMINGMODELClassicalrealtimeapplicationsinresearchareimplementedwithrealtimekernelslikeOS9orVxWorks,thatfollowanasynchronousparallelprogrammingapproach,asdefinedinPOSIX5,forexample.Thesoftwaredeveloperstructureshisprogramintasksaccordingtothelogicalstructureoftheproblemtosolve.Thesetasksareexecutedquasiparallelbytheoperatingsystem,andtheexecutionisbasicallyeventtriggered.Byassigningprioritiestothetaskstheprogrammergiveshintstotheoperatingsystemaboutthedesiredexecutionorder.Thustheprogrammerdoesnothavetoplantheschedulingdetails.Ontheotherhanditisdifficulttounderstandtheexecutionorderandtodecide,ifaspecifictaskcanmeetitsdeadlines.TheprogrammingmechanismsinPLCsystemsaretotallydifferent,becausetheyfollowtheolderapproachofsynchronousprogramming6.Here,theexecutionoftasksiscompletelytimetriggered,andtheprogrammerhastoorganizehisprogramintotasksaccordingtothetime,whenataskhastorun.Sohemustplantheexecutionorderhimself,whichismorecomplicatedbutalsogivesmorecontrol.InStep7,thedevelopmentenvironmentoftheS7,allcodeexistsinblocks,asdefinedinIEC1131.TasksarerepresentedbyOrganizationBlocksOBs.OBsaretheschedulableitems,thatarecalledbytheoperatingsystemofthePLCatcertainevents,e.g.,whenatimerexpiresoranerroroccurs.Thus,theOBsaretheinterfaceoftheoperatingsystemtotheuserprogram.AsindicatedinFig.2,OBscancallFunctionsFCs,whichareblocksthatcorrespondtofunctionsinaprocedurallanguage.FCscancallotherFCsorsystemfunctionsSFCs,whichcorrespondtooperatingsystemcallsinaPOSIXenvironment.FunctionBlocksFBs/SystemFunctionBlocksSFCsareFCs/SFCswithanassigneddatablockforstaticfunctiondata.AnormalPLCprogramiscontainedinOB1,whichiscalledcyclicallybytheoperatingsystem,asindicatedinFig.3.BeforeOB1iscalledtheoperatingsystemtransfersdatafromtheinputmodulestoamemoryareacalledprocessimagetable.AfterOB1hasbeencalled,datafromtheprocessimagetableiscopiedtotheoutputmodules.TheindirectaccesstoI/Omodulesviatheprocessimagetablereducesaccesstimeandincreasesconsistency.KLEINESetal.SIMATIC®PLCOPERATION491Fig.3.ExecutionofmainprogramscancycleOB1.TheexecutiontimeofOB1ismonitored,andifapreconfiguredmaximumisexceeded,thetimeerrorOB80iscalled.OnS7400®andWinAC®alsoaminimumforthecycletimeofOB1canbeconfigured.IftheexecutiontimeforOB1islessthen,thebackgroundOB90iscalled,whichhasthelowestpriority.ThepriorityofallotherOBsincreaseswithitsnumber.OnlyonS7400®andWinAC®thisdefaultprioritycanbechanged.EachOBcanbeinterruptedbyOBswithahigherpriority.TableIliststhepossibleOBs.AvailabilityofOBsdependsontheCPUtype.IfmoreOBsofacertaintypearerequired,amoreexpensiveCPUhastobebought.TimeofdayinterruptOBsarestartedatapreconfiguredtime,e.g.,endofashift,whereastimedelaysinterruptOBsarestartedattheexpirationofaoneshottimer.CyclicinterruptOBsarestartedwithafixedfrequency.Thetimeintervalandthephaseoffsetcanbeconfiguredwithagranularityof1ms.HardwareinterruptsOBsarestartedbyaaneventataninputorfunctionmodule,e.g.,detectionoftherisingedgeofadigitalsignal.ThisfunctionalityisonlyavailablewithsocalledHighFeatureinputmodules.SynchronouserrorOBsarestartedbyerrorsintheuserprogram,whereasasynchronouserrorinterruptOBsarestartedbyPLCfaults,likepowerfailure,modulefailureortimeerrors.Atimeerroroccurs,whenanOBcannotmeetitsscheduledstarttime,andisanuniquefeatureofPLCs.III.REALTIMEPERFORMANCEMEASUREMENTSA.PerformanceEvaluationGoalsAkeyissueofrealtimeperformanceisthereactiontimetoexternalevents.BecausePLCsystemsbasicallyconformtoasynchronousprogrammingmodel,thisisdirectlydeterminedbythecycletime,whichhastobeanalyzedforthefreerunningcycleOB1andcyclicinterruptse.g.,OB35.TodeterminetheapplicationareaofPLCclasses,theminimumofhastobemeasuredfordifferentPLCtypes.TheactualvalueofinaspecificapplicationdependsontheamountofcodeinthecyclicOB,ofcourse.TABLEIOBTYPESOFASIMATIC®S7TABLEIIPLCSUNDERTESTDeterministicbehaviorofaPLCisdeterminedbythejitterof,whichisofprimaryinterestforcyclicinterrupts.WithHighFeatureinputmodules,alsohardwareinterruptsarepossible.Heretheminimumresponsetime,whichisdefinedasthetimetoactivateOB40,anditsjitterhastobemeasured.Inordertogetacompletepicture,themeasurementshavetobeconductedforaminiPLC,amidrangePLCandahighendPLC.TableIIshowstheCPUs,thathavebeenselectedforthemeasurementsinthispaper.Thetimeforafloatingpointadditionhasbeenmeasuredbyrepeatingittimes,inordertoconveyanimpressionoftheirrelativeperformance,whichdiffersconsiderably.BecauseofthedistributednatureofPLCbasedsystems,theimpactofPROFIBUScommunicationtoresponsetimeisanim492IEEETRANSACTIONSONNUCLEARSCIENCE,VOL.51,NO.3,JUNE2004Fig.4.Experimentsetup.Fig.5.HistogramofOB1cycletimeatIM151/CPU.portantissue.Thustheadditionaldelaysintroducedbycommunicationaswellastheadditionaljitterhavetobeanalyzed.Butpresentationofcommunicationrelatedmeasurementswouldgobeyondthescopeofthispaperandwillbecoveredbyafuturepublication.Theanalysisoftheresponsetimeasafunctionofthesystemload,e.g.,inducedbyharddiskactivity,communicationorbackgroundcomputing,isakeyissueonconventionalPOSIXlikerealtimesystems.ThisisnotanissueonPLCsystemsbecauseoftheirsynchronouscyclicoperation.EventhecommunicationonfieldbusseslikePROFIBUSDPV0orASInterfaceiscyclically,thusinducingaconstantload.Forasynchronoustypeofcommunication,e.g.,TCP/IP,intelligentcommunicationcontrollersareused,thusoffloadingtheCPU.AnexceptionfromthisruleistheMPIMultipointInterface,aproprietaryfieldbus,thatisintegratedineachCPU.ButinJülichMPIisonlyusedforprogramming.B.MeasurementScenarioAccordingtoFig.4theinputsofthePLCsundertestlistedinTableIIareconnectedtoapulsegenerator.OB40isactivatedbyarisingedgeoftheinputsignalandtogglesaoutputsignal.TheoutputofthepulsegeneratorandoutputsofthePLCundertestareconnectedtotheNationalInstrumentsanaloginputmoduleNI6062E.ThesignalsaresampledwithafreFig.6.HistogramofOB1cycletimeatCPU314C2DP.quencyof100kHz.Matlabcodehasbeendevelopedthatdetectsrisingedgesinthesampledsignals,computestherequiredtimedifferencesandformsanhistogramofthemeasureddata.ThusthedistributionoftheresponsetimeofthePLCcanbemeasured.Thedistributionofthecycletimeismeasuredinananalogousway.Alternatively,thesignalsareconnectedtotheTDCmoduleSIS3400fromStruckInnovativeSystems.Thusthecorrectnessandthesufficientprecisionofthemeasureddatacouldbeverified.C.MeasurementsoftheMainProgramScanCycleOB1Figs.5–7showthedistributionofforOB1measuredonthefirstthreePLCinTableI.TherewasnootheractivityonthesystemthanOB1,whichonlycontainedcodefortogglingadigitaloutputdirectlywithoutusingtheprocessimagetable.TheminimumforanditsjitterarecausedbyoperatingsystemactivitiesandgetbetterwithincreasingperformanceofthePLCundertest.AlthoughmevalueandvarianceoffortheS7300®aremuchbetterthanforIM151/CPUtheworstcaseiscomparable.CPU4122isalmostdetermistic,basicallytakingtwodiscretevalues.ThisisnotnecessarilycausedbyCPUbehavior,becauseatthesefrequenciesthebehaviorofthedigitaloutputsgetssignificant,too.ThiscausedartifactsontheCPU4141wherewemeasuredaminimumcycletimeof0.2ms.Butinthissituationthetimebetweentwostatechanges