关于PLC的中英文对照翻译.docx

关于PLC的中英文对照翻译.docx

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关于PLC的中英文对照翻译

原文：

PLCCommunicationusingPROFINET:

ExperimentalResultsandAnalysis

Abstract

PROFINETistheIndustrialEthernetStandarddevisedbyPROFIBUSInternationalfor“Ethernetontheplantfloor”.PROFINETallowstoimplementacomprehensivecommunicationssolutiononEthernetwhichincludespeer-to-peercommunicationbetweencontrollers,distributedI/O,machinesafety,motioncontrolanddataacquisition.Inthispaperananalysisisconductedonthepeer-to-peerinterlockingperformancebasedonPROFINETspecification.Testswereperformedtodeterminetheperformanceofthepeer-to-peercommunicationmechanism,toevaluatetheimpactofswitchesonthesystem,andtomeasuretheimpactofdatasizeonpeer-to-peercommunicationperformance.Thepapersummarizesthetestresults.

1.Introduction

Althoughawidevarietyofnetworksandfieldbuseshavebeenusedinthemanufacturingindustryoverthepastdecade[1],thewidespreadadoptionofEthernetasadefactostandardinotherdomains（e.g.,theinternet）hasmadeitanattractiveoptiontoconsider.Theincreasednetworkspeedandthereducedcostofdeviceshasfurtherheightenedinterest.TheintroductionofswitchedEthernethasallowedformoredeterministicbehaviorandalleviatedmanyoftheconcernsaboutunboundeddelays[2,3,4].Ethernetisalreadybeingwidelyusedasadiagnosticnetworkinmanufacturingsystemsandismakinginroadsintothecontrolnetworkingdomain[5,6].

However,standardEthernet（IEEE802.3）isnotadeterministicprotocol,andnetworkqualityofservicecannotbeguaranteed.Toaddressthisinherentnondeterminism,different“flavors”ofEthernethavebeenproposedforuseinindustrialautomation.SeveraloftheseaddlayersontopofstandardEthernetorontopoftheTCP/IPprotocolsuitetoenablethebehaviorofEthernettobemoredeterministic[7].However,thenetworksolutionsmaynolongerbe“Ethernet”otherthanatthephysicallayer.

Sincetimedelayisanimportantissueincontrolsystems,therehavebeenanumberofprojectsdevotedtoanalyzingandexperimentallytestingnetworkperformanceforuseincontrolsystems.Ithasbeenshownthatthelargestcomponentofthetimedelayinsendingmessagesfromonenodetoanotheristypicallynotonthenetworkitself,butrathertheapplicationlayerthatinterfacestothenetwork[8,9].ExperimentalanalyseshavebeencarriedouttospecificallyaddresstheissueofdelaysinswitchedEthernet[10,4].However,duetotherelativelyrecentintroductionofcommercialdevicesthatimplementthenewindustrialEthernetprotocols,therehavebeenonlyafewpublishedaccountsoftheiractualperformance[11,12].

Overthepastsixmonths,ourgroupattheUniversityofMichiganhasundertakenanindustrialEthernettestingproject[13].Thegoaloftheprojectwastoevaluatethesuitabilityofreal-timeEthernetforpeer-to-peercommunicationbetweenPLCsonafactoryfloor.ThepurposeofthispaperistosummarizetheresultsofourtestsonPROFINET,anddiscussourfindings.

Theoutlineofthepaperisasfollows.InSectionII,wesummarizehowPROFINETenablesreal-timecommunicationoverEthernet.InSectionIII,wedescribetheteststhatwereperformed.SectionIVpresentstheresultsofthosetests,andconclusionsaregiveninSectionV.

2.PROFINETCBAwithReal-TimeChannelCommunication

PROFINETdistinguishestwoviews:

PROFINETIOforintegrationofdistributedI/OandPROFINETCBA（ComponentBasedAutomation）forcreationofpeer-to-peercommunicationandinterlockingbetweencontrollersinmodularplants（Figure1）

AllotherPROFINETapplicationssuchassafety,motioncontrol,andHMI（HumanMachineInterface）arebasedonthesecommunicationmodes.PROFINETcommunicationisscalableinthreelevels:

PROFINETTCP/IPCommunication（NRT）enablescycletimesaslowas100ms,PROFINETReal-TimeCommunication（RT）enablescycletimesupto1-10msandIsochronousReal-TimeCommunication（IRT）enablescycletimesupto1mswithJitterlessthan1µs.

ComponentbasedcommunicationisrealizedthroughPROFINETCBAwhichusesselectivelytheTCP/IPortheReal-Time（RT）channel.CommunicationfordistributedI/OisimplementedthroughPROFINETI/OwhichusesReal-TimeandIsochronousReal-Time（IRT）communication.

PROFINETReal-TimeChannelThePROFINETRealTimeChannelisacycliccommunicationpathusedbyindividualstationstoexchangetimecriticaldataatperiodicintervalsspecifiedbytheprogrammer.ItisbasedontheIEEEandIECdefinitions[14],whichonlypermitalimitedtimeforexecutionofReal-Timeserviceswithinabuscycle.Real-TimedataarehandledwithhigherprioritythanNon-Real-Time（NRT）data.ThetightnessofthewindowdependsontheReal-Timecharacteristics.TheReal-TimemechanismisbasedonLayer2oftheOSImodelandseveralprotocollayersareomitted.Thusthecommunicationoverheadassociatedwithpreparingdata,transferringitandmakingitavailabletotheoverlyingapplicationforusearereduced.UsingEtherealitwasfoundthatthetotaloverheadassociatedwithCyclicRealTimecommunicationis56bytes.

3.TestsPerformed

Thefollowingtestsweredesignedtomeasuretheimpactofsystemparametersonpeer-to-peerinterlockingperformanceusingPROFINETCBAwithRTcommunicationmethod.Thesystemparametersincludedatasizeandnumberofswitches.Thetestsarevendorneutralsothatanyimplementationcanbeconfiguredtoundergoeachtest.Connectionfailuresorerrorsarenotincludedinthistestplan.Toperformteststhefollowingequipmentwasused:

onecomputerwithMatlabandtheprotocolanalyzerEthereal,SIMATICiMapandSTEP7asconfigurationsoftware,fiveswitchesfromHirschmannandtwoSiemensSIMATICPLCs（ProgrammableLogicControllers）.ThePLCswereconfiguredusingthefactorydefaultsforprocessorandcommunicationallocationoptions.TheHirschmannswitches（100Mbps）wereconfiguredforportspeedautonegotiation.DuetothefactthatPROFINETisbasedonUnicastcommunicationtheMulticastfunctionalitywasnotconfiguredintheswitches.

3.1PerformanceMetrics

TheperformancemetricsanalyzedarePLC1PacketTimeIntervalandRoundTripTimeInterval.

PLC1PacketTimeIntervalisthetimebetweentwosuccessivetransmittalsofpacketsfromPLC1.Ideally,thePLC1PacketTimeIntervalisalwaysexactlythesameastheconfiguredupdateintervalinthePLC.However,inpracticethereissomevariabilityassociatedwiththisinterval.Theexperimentalresultsthatfollowsummarizetheaverage（meanvalue）andthejitter（standarddeviation）ofthePLC1packettimeinterval.Thesemetrics（meanandstandarddeviation）areimportant,astheygiveameasureofthedeterminismthatcanbeobtainedforrealtimecontrolusingPROFINET.

RoundTripTimeIntervalisdefinedastheTimeIntervalneededforapacketfromPLC1toreachPLC2,beechoedandcomebacktoPLC1.ConsideratestwherePLC1generatesdataandPLC2echoesthembacktoPLC1throughaswitch.

Figure2showsthetimingchartforthecommunicationbetweenPLC1andPLC2wherePLC1sendsmessagesatT1,T2,T3,...andPLC2echoesatt1,t2,t3,....PLC1PacketTimeIntervalshouldbeequaltotheconfiguredupdateintervalonPLC1,andPLC2PacketTimeIntervalshouldbeequaltoconfiguredupdateintervalonPLC2.IftheechofromPLC2arrivesbeforeT2,thentheroundtripcountergetsincrementedandthenewvalueistransmittedfromPLC1atT2.SincetheincrementoftheroundtripcounteristakenforcalculationoftheRoundTripTimeInterval,inthiscaseitshouldbeequaltothePLC1PacketTimeInterval.Considerthecasewhent1shiftsrelativetoT2.ThentheechofromPLC2isreceivedafterT2,andtheroundtripcounterisnotincrementedinthemessagetransmittedfromPLC1atT2.Hence,theRoundTripTimeIntervalbecomestwicethePLC1PacketTimeInterval.

Figure2.Timingchart

FromtheaboveobservationsitisnoticedthatRoundTripTimeintervalmeanandstandarddeviationarealsoimportantasmeasuresofthedegreeofsynchronizationforreal-timecontrolusingPROFINET.

3.2TestDescriptions

Test1:

BenchmarkTest1isthebenchmarktest.TheothertestsarecomparedtoTest1.InthistestPLC1generateseightbytesofdataandPLC2echoesitbacktoPLC1throughaswitch.PLC1usesthelast4bytes（dint）ofthedataforanewdatareceivedcounter.PLC1incrementsthiscounterasdiscussedinsection3.1.

Toperformmeasurements,aPCrunningEtherealwasconnectedtothemanagedswitchwhichconnectstothePLCs.AllpacketsgoingtoandfromPLC2andtheirrespectivetimestampsweremirroredontothisport.

Test2:

NetworkSwitchesTheobjectiveofTest2istoevaluatetheimpactthatswitchesintroducetothesystem.ThenumberofswitchesbetweentwoPLCsisthetestvariable.ThesamevariablesaremeasuredasinTest1.WewillconsiderthecaseofthreeandfiveswitchesbetweenthePLCs.

Test3:

SizeofDataTheobjectiveofTest3istomeasuretheimpactofdatasizeonpeer-to-peercommunicationperformance.Thetestvariableisthedatasize.MeasurementsareperformedasdescribedinTest1.Wewillconsidertwocases.Inthefirstcase216bytesofunuseddata,inthesecond440bytesofunuseddata.

4.TestResults

Inperformingthetestsandanalyzingtheresultsadatacaptureof5000packetsperPLCisconsideredinordertoassessthetimingperformance.TheaverageandstandarddeviationvaluesofPLC1PacketTimeIntervalandRoundTripTimeIntervalaremeasuredinmillisecondsandroundedofftothreesignificantdigitsafterthedecimalpoint.Alltestsareperformedwithanupdatetimeof8mswhichistypicalfortheseapplicationsinthefactory.Figures3,4and5showthebenchmarktestresults,PLC1PacketTimeInterval,