可编程控制器应用中英文对照外文翻译文献.docx

可编程控制器应用中英文对照外文翻译文献.docx

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可编程控制器应用中英文对照外文翻译文献

中英文对照外文翻译

Supportsoftwareforthedevelopmentofprogrammablelogic

1、Introduction

ProgrammableLogicControllers（PLC）classofreal-timecomputersusedextensivelyinindustrialcontrolapplications.ThedevelopmentofaPLCapplicationrequirestheconfigurationoftheinputsandoutputsofthePLCarchitecture,thatistheselectionofthenumber,typeandaddressesoftheinputsandoutputsofthePLC,andthewritinganddebuggingoftheapplicationprogram.Programmingthesecomputersisusuallydoneinspecificgraphicalstructuredtextlanguages[Bekkum93,Hughes89,Jones83]andtheprogramdebuggingiscarriedoutinadevelopmentenvironment.Mostoftheavailableenvironments[SquareD90,Taylor90]allowprogramwritinginmorethanonelanguage,runningitbysteporinsegmentsontheactualPLCandcheckingwhethertheassumedlogicalrelationshipsbetweentheinputsandtheoutputsateachprogramsteporsegmentaresatisfied.Iaddition,theseenvironmentsofferengineeringsupport,suchasthepreparationofinput/outputwiringdiagramsandthegenerationoftheexecutablecodeoftheprogram.RecentversionsofcommerciallyavailableenvironmentsaresuppliedwithasoftwareemulatorofoneormorePLCunits.Thisallowstoperformprogramdebuggingwithouthavingaccesstotheprogrammablecontrolleritself.Also,theuseofemulatorsmakeseasierandeconomicallyaffordablethesimulationofalargenumberofprogramoperatingconditions.Bymakingsurethattheprogramoperatescorrectyunderallthecriticaloperatingconditions,theriskofimplementingaPLC-basedsystemthatdoesnotmeetthedesiredrequirementsisreduced.However,theultimategoalofadevelopmentenvironmentshouldbetoverifythefunctionalpropertiesandbehavioroftheprogramsinallthepossiblestatesthatthesprogramsandtheplantstheymayenter.

Intheliterature,variouslanguagesandgraphicalormathematicalformalismsareproposedforwritingorspecifyingreal-timeprograms.Thetimingand/orfunctionalperformanceoftheseprogramscanbeverifiedatcompiletimeormathematically.ADA[Ada83],RT-ASLAN[Auemheimer86],EUCLID[Kligerman86],PEARL[Halang91],FLEX[Lin88]aresomeoftheproposedandmostwidelyknownlanguages.Theirgraphicalormathematicalformalismsarebasedontheuseoffinitestateautomata[Alford77],Petri-Nets[Fedler93],dataflowdiagrams[Zave82]andmetrictemporallogic[Koymans90].Althoughalltheseformalmethodsandlanguagesrepresentsignificantadvancestotheproblemofreal-timeprogramverification,stilltheyhavenotreachedthematurityrequiredtodealwiththecomplexitiesoflargesoftwaresystems.Untilthesemethodsreachacertainlevelofmaturitywemustrelyonlessformalmethods,tunedtotheneedsofspecificclassesofreal-timesystems.

InthecaseofPLC,wemaycontinuetousesimulationasamethodtoreveallogicalerrorsinourprogramsandassesstheirbehaviorunderanincompletesetofpossibleprogramstates.Inaddition,wemayincludenewfacilitiesintheprogramdevelopmentenvironments,theuseofwhichwillreducetheprogrammingandengineeringeffortofanapplication.TheymaybeeditingandcompilationfacilitieswhichsupportapplicationprogramminginallthelanguagesdefinedintheIEC1131-3standard.Byusingtheselanguagesourprogrammingefficiencywillbeimprovedsignificantly,becauseeachoneofthemcanbeusedtoprogramthepartoftheapplicationforwhichitisappropriate,andyetthewholeapplicationcanbelinkedintoasingleexecutableprogram.Otherfacilitieswhichcanreduceengineeringeffortarethosewhichcanmakeeasierandmoremeaningfulthedeclarationoftheprograminputconditions.Thesefacilitieswillallowustostudyinagiventimingperiod,alargernumberofsimulationcasesthantheoneswemighthavestudiedwithoutthesefacilities.Furthermore,wemayexpandthescopeofthesimulationbyincludingasimulatoroftheplantwhichinteractswiththecomputer.Also,facilitiescanbeaddedtoassistinthebetterinterpretationofthegeneratedsimulationresults.Suchfacilitiesmayallowustoconfigurethedisplaysofthegenerateddatathewaywethinkappropriate,andanimatethesimulatedoperationoftheapplicationprogram.

Inthispaperanarchitectureandlanguageconstructsareproposedforasoftwareaidwhich~anbeusedtodeclareinputconditionstoaPLCprogram,emulatethePLCoperationandconfigurethedisplayoftheemulationresults.Thecoreofthearchitectureisthevirtualmachine,whichisasoftwaremodulewhichemulatestheoperationofaprogramwrittenforaspecificPLCinanyapplicationprogramminglanguage.Thevirtualmachineislinkedwithexecutablecodegeneratedfromtwoothersoftwaremoduleswhichinterpretinstructionsdefiningtheinputconditionstotheapplicationprogramandtheconfigurationoftheoutputdisplay.Ofcourse,theproposedfacilitiesdonotsolvetheproblemofthecompleteverificationofthetimingbehaviorofanapplicationprogram.However,whentheyarecomparedwiththefacilitiesofferedbyvariouscommerciallyavailableaids,toouropiniontheydosignificantlyreducethetimetakentotesttheexecutionofaPLCprogramunderalargenumberofpossibleinputconditions,ondifferentarchitecturesandinterprettheresults.AscaleddownexperimentalimplementationoffacilitiesforaspecificPLCmodelisusedtodemonstratethefeasibilityoftheproposedconcepts.Theoperationoftheexperimentalset-uphasbeenvalidatedwithdatatakenfromtheexecutionofsampleprogramonaspecificPLC.

1、PrinciplesofPLCOperation.

TheProgrammableLogicControllerisaspecialpurposedigitalcomputerdesignedtocontrolmachineorprocessoperationsbymeansofastoredprogramandfeedbackfrominput/outputfielddevices.Itiscomposedprimarilyoftwobasicsections:

theCentralProcessingUnit（PLC）andanInput/Output（I/O）interface.TheCPUencompassesallthenecessaryelementsthatformtheintelligenceofthesystem.ItisfurthersubdividedtotheProcessor,MemoryandPowersupply.TheCPUacceptsinputdatafromvariousinputfielddevices,executesthestoredprogramfromthememory,andsendsappropriatecommandstooutputfielddevices.TheInput/Outputsystemformstheinterfacebywhichthefielddevicesareconnectedtothecontroller.Itspurposeistoconditionthevarioussignalsreceivedfromorsenttofielddevices.ThroughthissystemtheCPUcansenseandmeasurephysicalquantitiesregardingamachineorprocess,suchasproximity,position,motion,leveltemperature,pressure,currentandvoltage.Basedonthestatussensedorvaluesmeasured,theCPU,throughthisinterfacesystem,issuescommandsthatcontrolvariousdevicessuchasvalves,motors,pumpsandalarms.ThemostcommontypeofI/Ointerfaceisthediscreteone.Thisinterfaceconnectsfieldinputoroutputdevices,whichprovideinputsignalsorreceivecommandsignalsoftheBooleantype.

Pushbuttons,limitswitchesandselectorswitchesaresomeofthedevicesthatprovideincomingsignalsofthistype,,whereastypicalfielddevicesthatcanbeandpositionvalves.ThenumericalI/Ointerfaceisanothertypeofinterface,providedinaPLCsystem.Itcanallowreadingorwritingamulti-bitdigitaloranalogdevice.Multi-bitdeviceseithergenerateorreceiveagroupofbitswhichisthedigitalrepresentationofadecimalnumberorananaloguequantity.ThisgroupofbitsishandledasaunitbytheCPUandcanbeinparallelform（BCDinputsoroutputs）orinserialform（pulseinputsoroutputs）.Typicalfielddevicesprovidingmulti-bitinputtoaPLCarethumbwheelswitches,barcodereadersandencoders,whereastypicaloutputdevicesareseven-segmentandintelligentdisplays.Theanaloguefielddevicesarethevarioussensors,motordrives,andprocessinstrumentsusedtomonitoraridcontrolphysicalvariablessuchastemperature,pressure,humidity,flow,etc.ThedeviceswhichmonitorphysicalvariablessendtotheI/OinterfaceanaloguevoltagesandcurrentswhichareconvertedbytheA/Dconverteroftheinterfacetoamulti-bitdigitalcode.Ontheotherhand,ananaloguedeviceusedtocontrolthevalueofaphysicalvariable,receivesfromtheinterfaceananaloguevoltageorcurrentasaresultofthedigitaltoanalogueconversionofdataproducedbytheCPU.

TheprocessoroftheCPUperformsallthemathematicaloperations,datahandlinganddiagnosticroutinesbyexecutingacollection,storedinthememory.Thiscollectionconsistsofsupervisoryprograms,thatarepermanentlystoredinthememory,andapplicationprograms.Thesupervisoryprograms,knownastheexecutive,allowcommunicationwiththeprocessorviaaprogrammingdeviceorotherperipheralmemorymanagement,monitoringoffielddevices,hardwarefaultdiagnosisandexecutionoftheapplicationprogramwrittenbytheuser.ThememoryorganizationandthewaytheapplicationprogramisexecutedunderthecontroloftheexecutivearetwofeatureswhichdistinguishaPLCfromanyothergeneralpurposecomputer.Ingeneral,allPLChavememoryallocatedforexecutiveprograms,processorworkarea,datatableandapplicationprogram.TheprogrammedinstructionsandanydatathatwillbeutilizedbytheprocessortoperformitscontrolfunctionsarestoredintheApplicationProgramMemoryAreaandDataTableMemoryArearespectively.Thesetwoareascanbegroupedintowhatiscalledapplicationmemory.Eachcontrollerhasamaximumamountofapplicationmemorywhichispartofthetotalmemoryspecifiedforthecontroller.TheDataTableisfunctionallydividedIntotheInputTable,InternalStorageAreaandStorageRegistersArea.TheInputTableisanarrayofbitsthatstoresthesta