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1、山东科技大学学士学位论文附录ProgrammablelogiccontrollerCynthiaCooperFromWikipedia,thefreeencyclopediaAprogrammablelogiccontrollerorsimplyprogrammablecontrollerisadigitalcomputerusedforautomationofindustrialprocesses,suchascontrolofmachineryonfactoryassemblylines.Unlikegeneral-purposecomputers,thePL
2、Cisdesignedformultipleinputsandoutputarrangements,extendedtemperatureranges,immunitytoelectricalnoise,andresistancetovibrationandimpact.Programstocontrolmachineoperationaretypicallystoredinbattery-backedornon-volatilememory.APLCisanexampleofarealtimesystemsinceoutputresultsmustbeprodu
3、cedinresponsetoinputconditionswithinaboundedtime,otherwiseunintendedoperationwillresult.FeaturesControlpanelwithPLC(greyelementsinthecenter).Theunitconsistsofseparateelements,fromlefttoright;powersupply,controller,relayunitsforinputandoutput.ThemaindifferencefromothercomputersisthatPL
4、Csarearmoredforseverecondition(dust,moisture,heat,cold,etc)andhavethefacilityforextensiveinput/output(I/O)arrangements.TheseconnectthePLCtosensorsandactuators.PLCsreadlimitswitches,analogprocessvariables(suchastemperatureandpressure),andthepositionsofcomplexpositioningsystems.Someeven
5、usemachinevision.Ontheactuatorside,PLCsoperateelectricmotors,pneumaticorhydrauliccylinders,magneticrelaysorsolenoids,oranalogoutputs.Theinput/outputarrangementsmaybebuiltintoasimplePLC,山东科技大学学士学位论文附录orthePLCmayhaveexternalI/OmodulesattachedtoacomputernetworkthatplugsintothePLC.PLCswer
6、einventedasreplacementsforautomatedsystemsthatwouldusehundredsorthousandsofrelays,camtimers,anddrumsequencers.Often,asinglePLCcanbeprogrammedtoreplacethousandsofrelays.Programmablecontrollerswereinitiallyadoptedbytheautomotivemanufacturingindustry,wheresoftwarerevisionreplacedthere-wi
7、ringofhard-wiredcontrolpanelswhenproductionmodelschanged.ManyoftheearliestPLCsexpressedalldecisionmakinglogicinsimpleladderlogicwhichappearedsimilartoelectricalschematicdiagrams.Theelectricianswerequiteabletotraceoutcircuitproblemswithschematicdiagramsusingladderlogic.Thisprogramnotat
8、ionwa
