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IEEETRANSACTIONSONNUCLEARSCIENCE,VOL51,NO3,JUNE2004489MEASUREMENTOFREALTIMEASPECTSOFSIMATICPLCOPERATIONINTHECONTEXTOFPHYSICSEXPERIMENTSHARALDKLEINES,JANOSSARKADI,FRANKSUXDORF,ANDKLAUSZWOLLABSTRACTTODAY,MOSTSLOWCONTROLSYSTEMSFORPHYSICSEXPERIMENTSATFORSCHUNGSZENTRUMJLICHAREIMPLEMENTEDWITHPROGRAMMABLELOGICCONTROLLERPLCTECHNOLOGYANDFIELDBUSSYSTEMSINMANYCASES,EVENDETERMINISTICRESPONSEISREQUIREDFROMTHEPLCSTHISRAISESTHEQUESTIONABOUTTHEREALTIMEPERFORMANCETHATCANBEEXPECTEDFROMAPLCRESPONSETIMEMEASUREMENTSOFSIMATICPLCSMANUFACTUREDBYTHEWORLDMARKETLEADERSIEMENSAREPRESENTEDINFLUENCEOFPROGRAMSTRUCTUREANDHARDWARECONFIGURATIONONPERFORMANCEANDDETERMINISTICBEHAVIOROFAPLCISDISCUSSEDIPROGRAMMABLELOGICCONTROLLERSPLCSINEXPERIMENTCONTROLSYSTEMSTODAY,INDUSTRIALAUTOMATIONTECHNOLOGYISWELLESTABLISHEDININFRASTRUCTURESYSTEMSFORPHYSICSEXPERIMENTS,EG,INWATERORGASSUPPLYSYSTEMSTHISLEADSTOTHEHEAVYUSEOFPROGRAMMABLELOGICCONTROLLERSPLCS,WHICHTYPICALLYARETHEINTELLIGENTAUTOMATIONSTATIONSFORMINGTHECOREOFINDUSTRIALSYSTEMS1MAINREASONSINCLUDELOWPRICESINDUCEDBYMASSMARKET；ROBUSTNESS；LONGTERMAVAILABILITYANDSUPPORTFROMMANUFACTURER；PROFESSIONALITYCONNECTORS,CONFORMANCETOSTANDARDS,BEYONDTHESCOPEOFPUREINFRASTRUCTURESYSTEMS,PLCSAREINCREASINGLYBECOMINGCENTRALCOMPONENTSOFEXPERIMENTCONTROLSYSTEMS,REPLACINGVMEORPCBASEDREALTIMESYSTEMS2,3THISISCAUSEDBYTHEFOLLOWINGFEATURESOFMODERNPLCFAMILIESHIGHDEGREEOFSCALABILITYMODERNPLCFAMILIESHAVEAWIDESPECTRUMOFCPUTYPES,THATISSCALABLENOTONLYWITHREGARDTOPERFORMANCE,BUTALSOWITHREGARDTOFUNCTIONALITYANDFORMFACTORFOROUTDOORORFAULTTOLERANTAPPLICATIONSSPECIALVERSIONSAREAVAILABLEEXTENSIBILITYTHEMODULARDESIGNOFPLCSENABLESTHEEXTENSIONWITHAWIDERANGEOFDIGITALANDANALOGI/OMODULESADDITIONALLY,INTEGRATEDTECHNOLOGYMODULESAREAVAILABLEFORDIFFERENTAPPLICATIONAREAS,EG,STEPPERMOTORCONTROLLERS,SERVOMOTORCONTROLLERS,ORPIDCONTROLLERSEXTENSIVECOMMUNICATIONCAPABILITIESMODERNPLCSHAVEATLEASTONEINTEGRATEDCOMMUNICATIONPORTANDCANBEEXTENDEDBYAVARIETYOFCOMMUNICATIONCONTROLLERSMANUSCRIPTRECEIVEDMAY16,2003；REVISEDOCTOBER1,2003THEAUTHORSAREWITHZENTRALLABORFRELEKTRONIK,FORSCHUNGSZENTRUMJLICH,D52425JLICH,GERMANYEMAILHKLEINESFZJUELICHDEDIGITALOBJECTIDENTIFIER101109/TNS2004828504FORDIFFERENTFIELDANDPROCESSBUSSYSTEMS,THUSENABLINGCONNECTIONOFOTHERINDUSTRIALDEVICESAKEYISSUEISTHEEXTENSIONOFACENTRALPLCSYSTEMWITHDECENTRALPERIPHERYVIASPECIALFIELDBUSSESEG,PROFIBUSDP,THATALLOWSTHETRANSPARENTCONNECTIONOF“UNINTELLIGENT”I/OMODULESTHUSAPLCPROGRAMCANACCESSTHISDECENTRALPERIPHERYINTHESAMEWAYASCENTRALPLCPERIPHERYPOWERFULDEVELOPMENTENVIRONMENTMODERNPLCFAMILIESCOMEWITHAHOMOGENEOUSCROSSDEVELOPMENTENVIRONMENT,THATSUPPORTSALLTHEMAJORIEC1131PROGRAMMINGLANGUAGES4TYPICALLY,REPRESENTATIONSININSTRUCTIONLISTIL,FUNCTIONBLOCKDIAGRAMFBDORLADDERDIAGRAMLDCANBESWITCHEDDYNAMICALLYTHEDEVELOPMENTTOOLSALLOWSEMIGRAPHICALHARDWARECONFIGURATION,OFFERSTRONGDEBUGGINGMECHANISMSANDALLOWINCREMENTALDEVELOPMENTBYTHEEXCHANGEOFBLOCKSDURINGRUNTIMETODAY,INFZJUELICH,ALLNEWANDADVANCEDEXPERIMENTCONTROLSYSTEMSAREHEAVILYPLCBASED3,ASILLUSTRATEDBYTHEARCHITECTUREOFANEUTRONSPECTROMETERCONTROLSYSTEMSHOWNINFIG1BECAUSETHEWORLDMARKETLEADERSIEMENSDOMINATESTHEEUROPEANMARKET,SIMATICS7PLCSAREUSEDINFZJUELICH,ALMOSTEXCLUSIVELYTHEMIDRANGESERIESS7300ISMOSTPOPULARTHEHIGHENDSERIESS7400ISTARGETEDATAPPLICATIONSWITHEXTREMEPERFORMANCEREQUIREMENTSANDSUPPORTSALSOMULTIPROCESSORCONFIGURATIONSTHEMINIPLCSERIESS7200ISRARELYUSED,BECAUSEITGOTTHENAMES7BYPUREMARKETINGREASONSANDITSPROGRAMMINGENVIRONMENTISINCOMPATIBLETOTHEOTHERS7DEVICESINSTEADOFTHES7200,THEIM151/CPUSERVESASAMINIPLCTHEIM151/CPUISANINTELLIGENTCONTROLLERFORTHEDECENTRALPERIPHERYFAMILYET200SALSOTHEDECENTRALPERIPHERYSYSTEMSET200LANDET200MAREUSEDCOMMONLYINJLICHTHESOFTPLCWINACHASONLYBEENTESTEDINTHELAB,SOFARTHERESPONSIBLEPLANNINGOFPLCBASEDCONTROLSYSTEMSREQUIRESKNOWLEDGEONTHEIRREALTIMEFEATURESWHATISTHEMAGNITUDEOFPLCRESPONSETIME,DEPENDINGONPLCTYPECANDEADLINESBEGUARANTEEDWHATPROGRAMMINGRULESHAVETOBEFOLLOWEDTHEPAPERADDRESSESTHESEISSUESBYMEASUREMENTSATDIFFERENTPLCTYPESOFTHESIMATICS7FAMILYTHESTANDARDIEC1131DEFINESACOMMONFRAMEWORKFORPLCFUNCTIONALITYANDPROGRAMMINGLANGUAGES4,WHICHALLTHEMAJORPLCMANUFACTURERSCONFORMTOTHUSGENERALRESULTSCANBEGENERALIZEDALSOTOTHEIRPLCFAMILIES00189499/0420002004IEEE490IEEETRANSACTIONSONNUCLEARSCIENCE,VOL51,NO3,JUNE2004FIG1CONTROLSYSTEMARCHITECTUREOFTHENEUTRONSPECTROMETERKWS3FIG2BLOCKCALLINGHIERARCHYIISIMATICS7PROGRAMMINGMODELCLASSICALREALTIMEAPPLICATIONSINRESEARCHAREIMPLEMENTEDWITHREALTIMEKERNELSLIKEOS9ORVXWORKS,THATFOLLOWANASYNCHRONOUSPARALLELPROGRAMMINGAPPROACH,ASDEFINEDINPOSIX5,FOREXAMPLETHESOFTWAREDEVELOPERSTRUCTURESHISPROGRAMINTASKSACCORDINGTOTHELOGICALSTRUCTUREOFTHEPROBLEMTOSOLVETHESETASKSAREEXECUTEDQUASIPARALLELBYTHEOPERATINGSYSTEM,ANDTHEEXECUTIONISBASICALLYEVENTTRIGGEREDBYASSIGNINGPRIORITIESTOTHETASKSTHEPROGRAMMERGIVESHINTSTOTHEOPERATINGSYSTEMABOUTTHEDESIREDEXECUTIONORDERTHUSTHEPROGRAMMERDOESNOTHAVETOPLANTHESCHEDULINGDETAILSONTHEOTHERHANDITISDIFFICULTTOUNDERSTANDTHEEXECUTIONORDERANDTODECIDE,IFASPECIFICTASKCANMEETITSDEADLINESTHEPROGRAMMINGMECHANISMSINPLCSYSTEMSARETOTALLYDIFFERENT,BECAUSETHEYFOLLOWTHEOLDERAPPROACHOFSYNCHRONOUSPROGRAMMING6HERE,THEEXECUTIONOFTASKSISCOMPLETELYTIMETRIGGERED,ANDTHEPROGRAMMERHASTOORGANIZEHISPROGRAMINTOTASKSACCORDINGTOTHETIME,WHENATASKHASTORUNSOHEMUSTPLANTHEEXECUTIONORDERHIMSELF,WHICHISMORECOMPLICATEDBUTALSOGIVESMORECONTROLINSTEP7,THEDEVELOPMENTENVIRONMENTOFTHES7,ALLCODEEXISTSINBLOCKS,ASDEFINEDINIEC1131TASKSAREREPRESENTEDBYORGANIZATIONBLOCKSOBSOBSARETHESCHEDULABLEITEMS,THATARECALLEDBYTHEOPERATINGSYSTEMOFTHEPLCATCERTAINEVENTS,EG,WHENATIMEREXPIRESORANERROROCCURSTHUS,THEOBSARETHEINTERFACEOFTHEOPERATINGSYSTEMTOTHEUSERPROGRAMASINDICATEDINFIG2,OBSCANCALLFUNCTIONSFCS,WHICHAREBLOCKSTHATCORRESPONDTOFUNCTIONSINAPROCEDURALLANGUAGEFCSCANCALLOTHERFCSORSYSTEMFUNCTIONSSFCS,WHICHCORRESPONDTOOPERATINGSYSTEMCALLSINAPOSIXENVIRONMENTFUNCTIONBLOCKSFBS/SYSTEMFUNCTIONBLOCKSSFCSAREFCS/SFCSWITHANASSIGNEDDATABLOCKFORSTATICFUNCTIONDATAA“NORMAL”PLCPROGRAMISCONTAINEDINOB1,WHICHISCALLEDCYCLICALLYBYTHEOPERATINGSYSTEM,ASINDICATEDINFIG3BEFOREOB1ISCALLEDTHEOPERATINGSYSTEMTRANSFERSDATAFROMTHEINPUTMODULESTOAMEMORYAREACALLEDPROCESSIMAGETABLEAFTEROB1HASBEENCALLED,DATAFROMTHEPROCESSIMAGETABLEISCOPIEDTOTHEOUTPUTMODULESTHEINDIRECTACCESSTOI/OMODULESVIATHEPROCESSIMAGETABLEREDUCESACCESSTIMEANDINCREASESCONSISTENCYKLEINESETALSIMATICPLCOPERATION491FIG3EXECUTIONOFMAINPROGRAMSCANCYCLEOB1THEEXECUTIONTIMEOFOB1ISMONITORED,ANDIFAPRECONFIGUREDMAXIMUMISEXCEEDED,THETIMEERROROB80ISCALLEDONS7400ANDWINACALSOAMINIMUMFORTHECYCLETIMEOFOB1CANBECONFIGUREDIFTHEEXECUTIONTIMEFOROB1ISLESSTHEN,THEBACKGROUNDOB90ISCALLED,WHICHHASTHELOWESTPRIORITYTHEPRIORITYOFALLOTHEROBSINCREASESWITHITSNUMBERONLYONS7400ANDWINACTHISDEFAULTPRIORITYCANBECHANGEDEACHOBCANBEINTERRUPTEDBYOBSWITHAHIGHERPRIORITYTABLEILISTSTHEPOSSIBLEOBSAVAILABILITYOFOBSDEPENDSONTHECPUTYPEIFMOREOBSOFACERTAINTYPEAREREQUIRED,AMOREEXPENSIVECPUHASTOBEBOUGHTTIMEOFDAYINTERRUPTOBSARESTARTEDATAPRECONFIGUREDTIME,EG,ENDOFASHIFT,WHEREASTIMEDELAYSINTERRUPTOBSARESTARTEDATTHEEXPIRATIONOFAONESHOTTIMERCYCLICINTERRUPTOBSARESTARTEDWITHAFIXEDFREQUENCYTHETIMEINTERVALANDTHEPHASEOFFSETCANBECONFIGUREDWITHAGRANULARITYOF1MSHARDWAREINTERRUPTSOBSARESTARTEDBYAANEVENTATANINPUTORFUNCTIONMODULE,EG,DETECTIONOFTHERISINGEDGEOFADIGITALSIGNALTHISFUNCTIONALITYISONLYAVAILABLEWITHSOCALLED“HIGHFEATURE”INPUTMODULESSYNCHRONOUSERROROBSARESTARTEDBYERRORSINTHEUSERPROGRAM,WHEREASASYNCHRONOUSERRORINTERRUPTOBSARESTARTEDBYPLCFAULTS,LIKEPOWERFAILURE,MODULEFAILUREORTIMEERRORSATIMEERROROCCURS,WHENANOBCANNOTMEETITSSCHEDULEDSTARTTIME,ANDISANUNIQUEFEATUREOFPLCSIIIREALTIMEPERFORMANCEMEASUREMENTSAPERFORMANCEEVALUATIONGOALSAKEYISSUEOFREALTIMEPERFORMANCEISTHEREACTIONTIMETOEXTERNALEVENTSBECAUSEPLCSYSTEMSBASICALLYCONFORMTOASYNCHRONOUSPROGRAMMINGMODEL,THISISDIRECTLYDETERMINEDBYTHECYCLETIME,WHICHHASTOBEANALYZEDFORTHEFREERUNNINGCYCLEOB1ANDCYCLICINTERRUPTS；EG,OB35TODETERMINETHEAPPLICATIONAREAOFPLCCLASSES,THEMINIMUMOFHASTOBEMEASUREDFORDIFFERENTPLCTYPESTHEACTUALVALUEOFINASPECIFICAPPLICATIONDEPENDSONTHEAMOUNTOFCODEINTHECYCLICOB,OFCOURSETABLEIOBTYPESOFASIMATICS7TABLEIIPLCSUNDERTESTDETERMINISTICBEHAVIOROFAPLCISDETERMINEDBYTHEJITTEROF,WHICHISOFPRIMARYINTERESTFORCYCLICINTERRUPTSWITH“HIGHFEATURE”INPUTMODULES,ALSOHARDWAREINTERRUPTSAREPOSSIBLEHERETHEMINIMUMRESPONSETIME,WHICHISDEFINEDASTHETIMETOACTIVATEOB40,ANDITSJITTERHASTOBEMEASUREDINORDERTOGETACOMPLETEPICTURE,THEMEASUREMENTSHAVETOBECONDUCTEDFORAMINIPLC,AMIDRANGEPLCANDAHIGHENDPLCTABLEIISHOWSTHECPUS,THATHAVEBEENSELECTEDFORTHEMEASUREMENTSINTHISPAPERTHETIMEFORAFLOATINGPOINTADDITIONHASBEENMEASUREDBYREPEATINGITTIMES,INORDERTOCONVEYANIMPRESSIONOFTHEIRRELATIVEPERFORMANCE,WHICHDIFFERSCONSIDERABLYBECAUSEOFTHEDISTRIBUTEDNATUREOFPLCBASEDSYSTEMS,THEIMPACTOFPROFIBUSCOMMUNICATIONTORESPONSETIMEISANIM492IEEETRANSACTIONSONNUCLEARSCIENCE,VOL51,NO3,JUNE2004FIG4EXPERIMENTSETUPFIG5HISTOGRAMOFOB1CYCLETIMEATIM151/CPUPORTANTISSUETHUSTHEADDITIONALDELAYSINTRODUCEDBYCOMMUNICATIONASWELLASTHEADDITIONALJITTERHAVETOBEANALYZEDBUTPRESENTATIONOFCOMMUNICATIONRELATEDMEASUREMENTSWOULDGOBEYONDTHESCOPEOFTHISPAPERANDWILLBECOVEREDBYAFUTUREPUBLICATIONTHEANALYSISOFTHERESPONSETIMEASAFUNCTIONOFTHESYSTEMLOAD,EG,INDUCEDBYHARDDISKACTIVITY,COMMUNICATIONORBACKGROUNDCOMPUTING,ISAKEYISSUEONCONVENTIONALPOSIXLIKEREALTIMESYSTEMSTHISISNOTANISSUEONPLCSYSTEMSBECAUSEOFTHEIRSYNCHRONOUSCYCLICOPERATIONEVENTHECOMMUNICATIONONFIELDBUSSESLIKEPROFIBUSDPV0ORASINTERFACEISCYCLICALLY,THUSINDUCINGACONSTANTLOADFORASYNCHRONOUSTYPEOFCOMMUNICATION,EG,TCP/IP,INTELLIGENTCOMMUNICATIONCONTROLLERSAREUSED,THUSOFFLOADINGTHECPUANEXCEPTIONFROMTHISRULEISTHEMPIMULTIPOINTINTERFACE,APROPRIETARYFIELDBUS,THATISINTEGRATEDINEACHCPUBUTINJLICHMPIISONLYUSEDFORPROGRAMMINGBMEASUREMENTSCENARIOACCORDINGTOFIG4THEINPUTSOFTHEPLCSUNDERTESTLISTEDINTABLEIIARECONNECTEDTOAPULSEGENERATOROB40ISACTIVATEDBYARISINGEDGEOFTHEINPUTSIGNALANDTOGGLESAOUTPUTSIGNALTHEOUTPUTOFTHEPULSEGENERATORANDOUTPUTSOFTHEPLCUNDERTESTARECONNECTEDTOTHENATIONALINSTRUMENTSANALOGINPUTMODULENI6062ETHESIGNALSARESAMPLEDWITHAFREFIG6HISTOGRAMOFOB1CYCLETIMEATCPU314C2DPQUENCYOF100KHZMATLABCODEHASBEENDEVELOPEDTHATDETECTSRISINGEDGESINT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