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1、ProgrammableLogicControllers(PLCS)1AboutProgrammableLogicControllers(PLCs)PLCs(programmablelogiccontrollers)arethecontrolhubsforawidevarietyofautomatedsystemsandprocesses.Theycontainmultipleinputsandoutputsthatusetransistorsandothercircuitrytosimulateswitchesandrelaystocontro
2、lequipment.Theyareprogrammableviasoftwareinterfacedviastandardcomputerinterfacesandproprietarylanguagesandnetworkoptions.ProgrammablelogiccontrollersI/Ochannelspecificationsincludetotalnumberofpoints,numberofinputsandoutputs,abilitytoexpand,andmaximumnumberofchannels. Numbero
3、fpointsisthesumoftheinputsandtheoutputs.PLCsmaybespecifiedbyanypossiblecombinationofthesevalues. Expandableunitsmaybestackedorlinkedtogethertoincreasetotalcontrolcapacity. Maximumnumberofchannelsreferstothemaximumtotalnumberofinputandoutputchannelsinanexpandedsystem. PLCsyste
4、mspecificationstoconsiderincludescantime,numberofinstructions,datamemory,andprogrammemory. ScantimeisthetimerequiredbythePLCtocheckthestatesofitsinputsandoutputs. Instructionsarestandardoperations(suchasmathfunctions)availabletoPLCsoftware. Datamemoryisthecapacityfordatastora
5、ge. Programmemoryisthecapacityforcontrolsoftware.AvailableinputsforprogrammablelogiccontrollersincludeDC,AC,analog,thermocouple,RTD,frequencyorpulse,transistor,andinterruptinputs. OutputsforPLCsincludeDC,AC,relay,analog,frequencyorpulse,transistor,andtriac. Programmingoptions
6、forPLCsincludefrontpanel,handheld,andcomputer.Programmablelogiccontrollersuseavarietyofsoftwareprogramminglanguagesforcontrol. TheseincludeIEC61131-3,sequentialfunctionchart(SFC),functionblockdiagram(FBD),ladderdiagram(LD),structuredtext(ST),instructionlist(IL),relayladderlog
7、ic(RLL),flowchart,C,andBasic. TheIEC61131-3programmingenvironmentprovidessupportforfivelanguagesspecifiedbytheglobalstandard:SequentialFunctionChart,FunctionBlockDiagram,LadderDiagram,StructuredText,andInstructionList.Thisallowsformulti-vendorcompatibilityandmulti-languagepro
8、gramming. SFCisagraphicallanguagethatprovidescoordinationofprogramse
