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1、Chapter3IndustrialAutomationUnit11PLCSystemsUnit12PLCProgrammingUnit13IntroductiontoFieldbusUnit14WhyHMIsAreEverywhereUnit158051MicrocontrollerArchitectureUnit16HowtoStartWorkingwithaMicrocontrollerUnit11PLCSystemsNEMA,theNationalElectricalManufacturersAssociationdefinesaprogrammablelogiccontro
2、ller(PLC)as:Aprogrammablecontrollerisadigitallyoperatingelectronicapparatuswhichusesaprogrammablememoryfortheinternalstorageofinstructionsforimplementingspecificfunctions,suchaslogic,sequencing,timing,countingandarithmetic,tocontrolthroughdigitaloranaloginput/output,varioustypesofmachinesorproc
3、essasshowninFig.3.11.1.Programmablelogiccontrollers,programmablecontrollers,orPLCsarespecializedindustrialcomputers.下一页返回Unit11PLCSystemsThePLCacceptsinputsfromswitchesandsensors,evaluatesthesebasedonaprogram(logic),andchangesthestateofoutputstocontrolamachineorprocess.BriefhistoryofthePLCThead
4、ventofthePLCbeganinthe1960’sand1970’storeplacetraditional“hard-wired”controls,andhassincebecomethepredominantchoiceforindustrialcontrols.BeforePLCs,muchofmachinecontrolreliedoncontactsandrelaysprovidinghard-wired“logic”formachinecontrols.Changestothelogicwerelaborintensiveandcostly.上一页下一页返回Unit
5、11PLCSystemsIn1968,GM’shydramaticdivisionspecifiedthedesigncriteriaforwhatwouldbecomethefirstprogrammablelogiccontroller.BasicPLCcomponentsProgrammablecontrollershavegrownthroughoutindustrialcontrolapplicationsbecauseoftheeasetheybringtocreatingacontroller:easeofprogramming,easeofwiring,easeofi
6、nstallation,andeaseofchanging.PLCsspanawiderangeofsizes,butallcontainsixbasiccomponentsasshowninFig.3.11.2上一页下一页返回Unit11PLCSystemsRackassemblyMostmediumtolargePLCsystemsareassembledsuchthattheindividualcomponents—CPU,Input/Output,PowerSupply—aremodulesthatareheldtogetherwithinarack.InsmallerPLC
7、systems—allofthesecomponentsmaybecontainedinasinglehousingor“brick”—thesesmallersystemsaresometimesreferredtoas“bricks”or“shoebox”PLCs.PowersupplyThepowersupplyprovidespowerforthePLCsystem.ThepowersupplyprovidesinternalDCcurrentto
