外文翻译关于PLC的外文及翻译.docx

外文翻译关于PLC的外文及翻译.docx

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外文翻译关于PLC的外文及翻译

外文翻译-关于PLC的外文及翻译

PLCs--Past,PresentandFuture

Everyoneknowsthere'sonlyoneconstantinthetechnologyworld,andthat'schange.ThisisespeciallyevidentintheevolutionofProgrammableLogicControllers（PLC）andtheirvariedapplications.Fromtheirintroductionmorethan30yearsago,PLCshavebecomethecornerstoneofhundredsofthousandsofcontrolsystemsinawiderangeofindustries.

Atheart,thePLCisanindustrializedcomputerprogrammedwithhighlyspecializedlanguages,anditcontinuestobenefitfromtechnologicaladvancesinthecomputerandinformationtechnologyworlds.Themostprominentofwhichisminiaturizationandcommunications.

TheShrinkingPLC

WhenthePLCwasfirstintroduced,itssizewasamajorimprovement-relativetothehundredsofhard-wiredrelaysandtimersitreplaced.AtypicalunithousingaCPUandI/Owasroughlythesizeofa19televisionset.Throughthe1980sandearly1990s,modularPLCscontinuedtoshrinkinfootprintwhileincreasingincapabilitiesandperformance（seeDiagram1fortypicalmodularPLCconfiguration）.

Inrecentyears,smallerPLCshavebeenintroducedinthenanoandmicroclassesthatofferfeaturespreviouslyfoundonlyinlargerPLCs.ThishasmadespecifyingalargerPLCjustforadditionalfeaturesorperformance,andnotincreasedI/Ocount,unnecessary,aseventhoseinthenanoclassarecapableofEthernetcommunication,motioncontrol,on-boardPIDwithautotune,remoteconnectivityandmore.

PLCsarealsonowwell-equippedtoreplacestand-aloneprocesscontrollersinmanyapplications,duetotheirabilitytoperformfunctionsofmotioncontrol,dataacquisition,RTU（remotetelemetryunit）andevensomeintegratedHMI（humanmachineinterface）functions.Previously,thesefunctionsoftenrequiredtheirownpurpose-builtcontrollersandsoftware,plusaseparatePLCforthediscretecontrolandinterlocking.

TheGreatCommunicator

Possiblythemostsignificantchangeinrecentyearsliesinthecommunicationsarena.Inthe1970sModiconintroductionofModbuscommunicationsprotocolallowedPLCstocommunicateoverstandardcabling.ThistranslatestoanabilitytoplacePLCsincloserproximitytorealworlddevicesandcommunicatebacktoothersystemcontrolsinamainpanel.situation,fullyunderstandtheintentionoftheleadership,toensuretheoutput,quality,andconstantlyimprovethequalityofmanuscript.Amanuscriptqualityappraisalsystem,theimplementationofquantitativeassessment,eachquarterthecomparisonofofficedraftmanuscriptquality.Establisharewardsystemtorewardtheoutstandingmanuscriptselectionout,thewronginvestigatedpersons

Inthepast30yearswehaveseenliterallyhundredsofproprietaryandstandardprotocolsdeveloped,eachwiththeirownuniqueadvantages.Today'sPLCshavetobedatacompilersandinformationgateways.Theyhavetointerfacewithbarcodescannersandprinters,aswellastemperatureandanalogsensors.Theyneedmultipleprotocolsupporttobeabletoconnectwithotherdevicesintheprocess.Andfurthermore,theyneedallthesecapabilitieswhileremainingcost-effectiveandsimpletoprogram.

AnotherprimarydevelopmentthathasliterallyrevolutionizedthewayPLCsareprogrammed,communicatewitheachotherandinterfacewithPCsforHMI,SCADAorDCSapplications,camefromthecomputingworld.

UseofEthernetcommunicationsontheplantfloorhasdoubledinthepastfiveyears.Whileserialcommunicationsremainpopularandreliable,Ethernetisfastbecomingthecommunicationsmediaofchoicewithadvantagesthatsimplycan'tbeignored,suchas:

*Networkspeed.*Easeofusewhenitcomestothesetupandwiring.*Availabilityofoff-the-shelfnetworkingcomponents.*Built-incommunicationssetups.

IntegratedMotionControl

AnotherresponsibilitythePLChasbeentaskedwithismotioncontrol.Fromsimpleopen-looptomulti-axisapplications,thetrendhasbeentointegratethisfeatureintoPLChardwareandsoftware.

Therearemanyapplicationsthatrequireaccuratecontrolatafastpace,butnotexactprecisionatblazingspeeds.Theseareapplicationswherethestand-alonePLCworkswell.ManynanoandmicroPLCsareavailablewithhigh-speedcountingcapabilitiesandhigh-frequencypulseoutputsbuiltintothecontroller,makingthemaviablesolutionforopen-loopcontrol.

Theonecaveatisthatthecontrollerdoesnotknowthepositionoftheoutputdeviceduringthecontrolsequence.Ontheotherhand,itsmainadvantageiscost.Evensimplemotioncontrolhadpreviouslyrequiredanexpensiveoptionmodule,andattimeswasrestrictedtomoresophisticatedcontrolplatformsinordertomeetsystemrequirements.

Moresophisticatedmotionapplicationsrequirehigher-precisionpositioninghardwareandsoftware,andmanyPLCsofferhigh-speedoptionmodulesthatinterfacewithservodrives.Mostdrivestodaycanaccepttraditionalcommandsfromhost（PLCorPC）controls,orprovidetheirowninternalmotioncontrol.Thetrendhereistointegratethemotioncontrolconfigurationintothelogiccontrollerprogrammingsoftwarepackage.

ProgrammingLanguages

ardtheoutstandingmanuscriptselectionout,thewronginvestigatedpersonstorewtationofquantitativeassessment,eachquarterthecomparisonofofficedraftmanuscriptquality.Establisharewardsystemretheoutput,quality,andconstantlyimprovethequalityofmanuscript.Amanuscriptqualityappraisalsystem,theimplemensituation,fullyunderstandtheintentionoftheleadership,toensu2

AfacetofthePLCthatreflectsboththepastandthefutureisprogramminglanguage.TheIEC61131-3standarddealswithprogramminglanguagesanddefinestwographicalandtwotextualPLCprogramminglanguagestandards:

*Ladderlogic（graphical）.*Functionblockdiagram（graphical）.*Structuredtext（textual）.Instructionlist（textual）.

Thisstandardalsodefinesgraphicalandtextualsequentialfunctionchartelementstoorganizeprogramsforsequentialandparallelcontrolprocessing.Basedonthestandard,manymanufacturersofferatleasttwooftheselanguagesasoptionsforprogrammingtheirPLCs.Ironically,approximately96percentofPLCusersrecentlystilluseladderdiagramstoconstructtheirPLCcode.Itseemsthatladderlogiccontinuestobeatopchoicegivenit'sperformedsowellforsolong.

HardwarePlatforms

ThemodernPLChasincorporatedmanytypesofCommercialofftheShelf（COTS）technologyinitsCPU.ThislatesttechnologygivesthePLCafaster,morepowerfulprocessorwithmorememoryatlesscost.TheseadvanceshavealsoallowedthePLCtoexpanditsportfolioandtakeonnewtaskslikecommunications,datamanipulationandhigh-speedmotionwithoutgivinguptheruggedandreliableperformanceexpectedfromindustrialcontrolequipment.

NewtechnologyhasalsocreatedacategoryofcontrollerscalledProgrammableAutomationControllers,orPACs.PACsdifferfromtraditionalPLCsinthattheytypicallyutilizeopen,modulararchitecturesforbothhardwareandsoftware,usingdefactostandardsfornetworkinterfaces,languagesandprotocols.TheycouldbeviewedasaPCinanindustrialPLC-likepackage.

TheFuture

A2005PLCProductFocusStudyfromReedResearchGrouppointedoutfactorsincreasinglyimportanttousers,machinebuildersandthosemakingthepurchasingdecisions.Thetoppicksforfeaturesofimportancewere.

*Theabilitytonetwork,anddosoeasily.Ethernetcommunicationsisleadingthechargeinthisrealm.Notonlyarenewprotocolssurfacing,butmanyoftheindustrydefactostandardserialprotocolsthathavebeenusedformanyyearsarebeingportedtoEthernetplatforms.TheseincludeModbus（ModbusTCP）,DeviceNet（Ethernet/IP）andProfibus（Profinet）.EthernetcommunicationmodulesforPLCsarereadilyavailablewithhigh-speedperformanceandflexibleprotocols.Also,manyPLCCPUsarenowavailablewithEthernetportsonboard,savingI/Oslotspace.PLCswillcontinuetodevelopmoresophisticatedconnectivitytoreportinformationtootherPLCs,system

stablisharewardsystemtorewardtheoutstandingmanuscriptselectionout,thewronginvestigatedpersonsisalsystem,theimplementationofquantitativeassessment,eachquarterthecomparisonofofficedraftmanuscriptquality.Eyofmanuscript.Amanuscriptqualityapprasituation,fullyunderstandtheintentionoftheleadership,toensuretheoutput,quality,andconstantlyimprovethequalit3

controlsystems,dataacquisition（SCADA）systemsandenterpriseresourceplanning（ERP）systems.Additionally,wirelesscommunicationswillcontinuetogainpopularity.

*TheabilitytonetworkPLCI/OconnectionswithaPC.ThesametrendsthathavebenefitedPLCnetworkinghavemigratedtotheI/Olevel.ManyPLCmanufacturersaresupportingthemostacceptedfieldbusnetworks,allowingPLCI/Otobedistributedoverlargephysicaldistances,orlocatedwhereitwaspreviouslyconsiderednearlyimpossible.ThishasopenedthedoorforpersonalcomputerstointerfacewithstandardPLCI/Osubsystemsbyusinginterfacecards,typicallysuppliedbythePLCmanufacturerorathirdpartydeveloper.NowthesechallenginglocationscanbemonitoredwithtodayaPC.Whereindustrial-gradecontrolenginesarenotrequired,theusercantakeadvantageofmoreadvancedsoftwarepackagesandhardwareflexibilityatalowercost.

*Theabilitytouseuniversalprogrammingsoftwareformultipletargets/platforms.Inthepastitwasexpectedthatanintelligentcontrollerwouldbecomplextoprogram.Thatisnolongerthecase.Usersarenolongerjusttrainedprogrammers,suchasdesignengineersorsystemsintegrators,butend-userswhoexpecteasier-to-usesoftwareinmorefamiliarformats.TheWindows-b