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1、英语原文:ProgrammablelogiccontrollerAprogrammablelogiccontroller(PLC)orsimplyprogrammablecontrollerisadigitalcomputerusedforautomationofindustrialprocesses,suchascontrolofmachineryonfactoryassemblylines.Unlikegeneral-purposecomputers,thePLCisdesignedformultipleinputsandoutputar
2、rangements,extendedtemperatureranges,immunitytoelectricalnoise,andresistancetovibrationandimpact.Programstocontrolmachineoperationaretypicallystoredinbattery-backedornon-volatilememory.APLCisanexampleofarealtimesystemsinceoutputresultsmustbeproducedinresponsetoinputconditio
3、nswithinaboundedtime,otherwiseunintendedoperationwillresult..FeaturesThemaindifferencefromothercomputersisthatPLCarearmoredforseverecondition(dust,moisture,heat,cold,etc)andhavethefacilityforextensiveinput/output(I/O)arrangements.TheseconnectthePLCtosensorsandactuators.PLCr
4、eadlimitswitches,analogprocessvariables(suchastemperatureandpressure),andthepositionsofcomplexpositioningsystems.Someevenusemachinevision.Ontheactuatorside,PLCoperateelectricmotors,pneumaticorhydrauliccylinders,magneticrelaysorsolenoids,oranalogoutputs.Theinput/outputarrang
5、ementsmaybebuiltintoasimplePLC,orthePLCmayhaveexternalI/OmodulesattachedtoacomputernetworkthatplugsintothePLC.PLCwereinventedasreplacementsforautomatedsystemsthatwouldusehundredsorthousandsofrelays,camtimers,anddrumsequencers.Often,asinglePLCcanbeprogrammedtoreplacethousand
6、sofrelays.Programmablecontrollerswereinitiallyadoptedbytheautomotivemanufacturingindustry,wheresoftwarerevisionreplacedthere-wiringofhard-wiredcontrolpanelswhenproductionmodelschanged.12ManyoftheearliestPLCexpressedalldecisionmakinglogicinsimpleladderlogicwhichappearedsimil
7、artoelectricalschematicdiagrams.Theelectricianswerequiteabletotraceoutcircuitproblemswithschematicdiagramsusingladderlogic.Thisprogramnotationwaschosentoreducetrainingdemandsfortheexistingtechnicians.OtherearlyPLCusedaformofinstructionlistprogramming,basedonastack-basedlogi
8、csolver.ThefunctionalityofthePLChasevolvedovertheyearstoincludesequentialrelaycont