PLC全英文課件.ppt

ProgrammableLogicControllers PLC byLily LiuQingping UEENEED007B Introduction Threepoints WhatisPLC HistoryanddevelopmentofPLCPLCStructure Learningoutcome UnderstandroughlyaboutPLCtechnologyincludingapplications historyanddevelopment hardwareandsoftware Candesignasimpleladderdiagramtocontrolthemotortostartandstop 1 WhatisPLC APLC ProgrammableLogicController isadevicethatcanreplacethenecessarysequentialrelaycircuitsforcontrolsystem itisadigitalcomputer sometimesitcanbecalledProgrammableController PC ThePLCworksbylookingatitsinputsanddependingupontheirstate turningon offitsoutputs WhereneedtousethePLC ThePLChavebeenwidelyusedinindustry suchasautomaticproductionline robothand machinerymanufacturing transportationsystems chemicalprocessfacilities andmanyothers TheautomotiveindustryisoneofthelargestusersofPLC Intheseapplications thePLCreplacedthehardwiredlogicwithrelayladderlogic aprogramminglanguagevisuallyresemblingthehardwiredlogicreducedthetimefordesigningacontrolsystemfrom6monthsdownto6days intelligentelectricmeterswithPLC ThePLChavebeenwidelyusedInthepowersystem suchasintelligentelectricmeterwithPLC Inourlife thePLChavebeenwidelyused washingmachine trafficlight musicfountain aircondition Althoughcomputercontroltechnologyhasusedwidelyinindustriesorinourlife PLCcontrolhavemoreadvantagesthancomputercontrolbecauseithashigherperformance lowerprice andsuperiorreliabilityinharshenvironments 2 Historyanddevelopment BeforethePLC theautomationcontrolsystemwasmainlycomposedoftimerelays contactors positionswitches currentrelays voltagerelays middlerelays speedingrelays controlbuttons airswitchandsoon Thesecontrolsystemarecomposedbyhardware Thatis Thesecontrolsystemsarehard wiredrelaysystems Whentheproductionrequirementshavechanged wemustchangethecontrolsystem thisbecomesveryexpensiveandtimeconsumingwhenthechangeisfrequent Andit sdifficulttorewiretherelays Sincerelaysaremechanicaldevicestheyalsohavealimitedlifetime Troubleshootingwasalsoquitetediouswhensomanyrelaysareinvolved Forexample primarycircuit controlcircuit Airswitch button motor Thermalrelay fuse contactor NeedanothersimplecontrolmethodwithsoftwareDigitalcomputers beinggeneral purposeprogrammabledevices weresoonappliedtocontrolofindustrialprocesses Earlycomputersrequiredspecialistprogrammers andstringentoperatingenvironmentalcontrolfortemperature cleanliness andpowerquality Usingageneral purposecomputerforprocesscontrolrequiredprotectingthecomputer Sotherearesomelimitationstousethecomputerinindustry Anditneedakindofcontrollerfordigitaloperationwhichisdesignedforindustrialapplicationspecially GeneralMotorsCompany GM isoneoftheworld slargestautomakers itwasfoundin1908 GMmanufacturescarsandtrucksin35countries TheglobalheadquartersisinAmerican andthereisabranchcompanyinShanghai Itproductscarssuchas Chevrolet Cadillac Buickandsoon In1968 GeneralMotorsCorporation GM issuedarequestforproposalsforanelectronicreplacementforhard wiredrelaysystems BecausetheefficiencyformakingcarsislowandthecostishighinGM In1969 theDEC DigitalEquipmentCorporation accordingtotherequirementsofGMhasresearchedanddevelopedtheworld sfirstPLC andthisPLCwasusedsuccessfullyintheproductionlineofGM SincetheyhasusedthePLCintheirproductionline theefficiencyisgreatlyincreasedandthecostisgreatlyreduced TheautomotiveindustryisstilloneofthelargestusersofPLC ProgrammingiseasytolearnForexample ifyouusethePLCtocontrolthemotor howtodesignthePLCprogram primarycircuit controlcircuit 3 PLCstructure1 Softwareprogram Positive reversecontrolcircuitofmotor Hard wiredcontrolsystem TheprogramofPLCissimilartothecontrolcircuitWecanonlyreplacethecomplexcontrolcircuitbyPLCcontrolsystem TheprogramofPLCissimple andit seasytochangetheprogramoncomputer StatementList STL LadderDiagram LAD SequentialFunctionChart SFC LAD STL SFC Thetypeofsoftwareprogram Usually weusetheladderdiagram LAD todesignaprogramforacontrolsystem Note TheProgramlanguagesfordifferentPLCisnotsame 2 Hardwarestructure ThepowersupplysectionTheCPUmoduleThememorysectionTheI Osection Inputmodule CPU Powersupply Memory outputmodule 1 CPUmodule Controller Processor Memorysection Processorsection The CPU iscalledthe controller or processor bydifferentmanufacturers buttheyhavethesamefunctions TheCPUmodulecanbedividedintotwosections theprocessorsectionandthememorysection TheCPUsectionmakesthedecisionsneededbythePLCsothatitcanoperateandcommunicatewithothermodules Steppeddown Rectified Filtered Regulated VoltageandCurrentprotected Statusindicator LowDCvoltage 2 Thepowersupply ItprovidestheoperatingDC DirectCurrent powertothePLCandI Omodules italsoincludesbatterybackup Thepowersupply PS sectiongetsitsinputpowerfromanexternal220VoltAC AlternatingCurrent source thePLChasan24VDCsource TheoutputofthePSprovideslowDCvoltagetothePLC svariousmodulesaswellastoitsbattery whichisusedforthememorybackup Theprograms LAD forthecontrolsystemhavebeenstoredinthismemorysection ThesememorylocationsarescannedbytheCPU Thememorywillreceive write mode digitalinformationorhavedigitalinformationaccessed read mode bytheCPU 3 Thememorysection 4 InputSection Receivestheexternalsignalandstatus Theexternalsignalhavetwoforms digitalsignalandanalogsignal Thissectionwilltransformanalogsignalintodigitalsignal 5 OutputSectionTheoutputmoduletransmitssignalstoactivatevariousdevicesanddisplaysthestatus throughtheuseofLED oftheconnectedoutputpoints Conclusion AProgrammableLogicControllerisadevicethatcanus