1、PLCProgrammableLogicControllers(PLCs)/alsoreferredtoasprogrammablecontrollers/areinthecomputerfamily/Theyareusedincommercialandindustrialapplications/APLCmonitorsinputs/makedecisionsbasedonitsprogram/andcontrolsoutputstoautomateaprocessormachine/Thiscourseismeanttosupplyyouwithbasicinformationonthef
2、unctionsandconfigurationsofPLCs/Inthe1960s/electromechanicaldevicesweretheorderofthedayasfarascontrolwasconcerned/Thesedevicescommonlyknownasrelays/werebeingusedbythethousandstocontrolmanySequential-typemanufacturingprocessesandStand-alonemachines/Manyoftheserelayswereinuseinthetransportationindustr
3、y/morespecifically/theautomothveindustry/Theserelaysusedhundredsofwiresandtheirinterconnectionstoaffectacontrolsolution/Theperformanceofarelaywasbasicallyreliableatleastasasingledevice/Butthecommonapplicationsforrelaypanelscalledfor300to500ormorerelays/andthereliabilityandmaintenanceissuesassociated
4、withsuppostingthesepenelsbecameaverygreatchallenge/Costbecameantherissue/forinspiteofthelowcostoftherelayitself/theinstalledcostofthepanelcouldbequitehigh/Thetotalcostinduelingpurchasedparts/wiring/andinstallationlabor/couldrangefrom$30-$50perrelay/Tomakemattersworse/theconstantlychangingneedsofapro
5、cesscalledforrecurringmodificationsofaconstantlychangingneedsofaprocesscalledforrecurringmodificationsofacontrolpanel/Withrelays/thiswasacostlyprospect/asitwasaccomplishedbyamajorrewiringeffortonthepanel/Inaddition/thesechangesweresometimespoorlydocumented/causingasecondshiftmaintencancenightmaremon
6、thslater/Inlightofthis/itwasnotuncommontodiscardanentirecontrolpanelinfavorofanewonewiththeappropriatecomponentswiredinamannersuitedforthenewprocess/Addtothistheunpredictable/andpotentiallyhight/costofmaintainingthesesystemsasonhigh-volumemotorvehideproductionlines/anditbecameclearthatsomethingwasne
7、ededtoimpronethecontrolprocesstomakeitmorereliable/easiertotroubleshoot/andmoreadaptabletochangingcontrolneeds/Thatsomething/inthelate1960s/wasthefirstprogrammablecontroller/Thisfirst“revollutionary”systemwasdevelopedasaspecificresponsetotheneedsofthemajorautomotinemanufacturersintheUnitedStates/the
8、seearlycontrollers/orprogrammablelogiccontrollers(PLC)/representedthefirstsystemsthat(1)couldbeusedonthefactoryfloor/(2)couldhavethere“logic”changewithoutextensiverewiringorcomponentchanges/and(3)wereeasytodiagnostandrepairwhenproblemsoccurred/Itisinterestingtoobservetheprogressthathasbeenmadeinthep
9、ast15yearsinthelate1960smusthavebeenconfusingandfrighteningtoagreatnumberofpeople/Forexample/whathappenedtothehardwiredandeletromechanicaldevicesthatmaintenancepersonnelwereusedtorepairingwithhardtools?Theywerereplacedwith“computers”disquisedaselectromicsdesignedtoreplacerelays/Eventheprogrammingtoo
10、lsweredesignedtoappearasrelayequivalentpresentations/Wehavetheopportunitynowtoexaminethepromise/inretrospect/whattheprogrammablecontrollerbroughtmanufacturing?Allprogrammalecontrollersconsistofthebasicfunctionalblocks/Wewillexamineeachblocktounderstandtherelathonshiptothecontrolsystem/Firstwelookeda
11、tthecenter/asitistheheardofthesystem/Itconsistsofamicroprocessor/logicmemoryforthestorageoftheactualcontrollogic/storageorvariablememoryforusewithdatathatwillordimarilychangeasafunctionofthecontrolpropramexecution/andapowersupplytoprovideelectricalpowerfortheprocessorandmemory/NextcomestheI/Oblock/T
12、hisfunctiontakestheconrtollevelsignalsfortheCPUandconvertsthemtovoltageandcurrentlevelssuitable/TheI/Otypecanrangefromdigital/analog/oravarietyofspecialpurpose“smart”I/Owhicharededicatedtoacertainapplicationtask/Theprogrammingisnormallyusedonlytoinitiallyconfigureandprogramasystemandisnotrequiredfor
13、thesystemtooperate/Itisalsousedintroubleshootingasystem/andcanprovetobeavaluabletoolinpinpointingtheexactcauseofaproblem/ThefielddevicesshownhererepresentthevarioussensorsandactuatorsconnectedtotheI/O/Thesearethearms/legs/eyes/andearsofthesystem/includingpushbuttons/limitswitches/proximitysuitches/p
14、hotosensors/thermocouple/positionsensingdevices/andbarcodereaderasinput；andpildtlight/displaydevices/motorstarters/DCandACdrivers/solenlids/andprintersasoutputs/1/BasicPLCOperationPLCsconsistofinputmodules/aCentralProcessingUnit(CPU)/andoutputmodulesorpoints/Aninputacceptsavarietyofdigitaloranalogsi
15、gnalsfromvariousfielddevices(sensors)andconvertsthemintoalogicsignalthatcanbeusedbytheCPU/TheCPUmakesdecisionsandexecutescontrolinstructionsbasedonprograminstructionsinmemory/OutputmodulesconvertcontrolinstructionsfromtheCPUintoadigitaloranalogsignalthatcanbeusedtocontrolvariousfielddevices(actuator
16、s)/Aprogrammingdeviceisusedtoinputthedesiredinstructions/TheseinstructionsdeterminewhatthePLCwilldoforaspecificinput/Anoperatorinterfacedeviceallowsprocessinformationtobedisplayedandnewcontrolparameterstobeentered/Pushbuttons(sensors)/inthissimpleexample/connectedtoPLCinputs/canbeusedtostartandstopa
17、motorconnectedtoaPLCthroughamotorstarter(actuator)/2/Hard-WiredControlPriortoPLCs/manyofthesecontroltasksweresolvedbycontactorsorrelaycontrols/Thisisoftenreferredtoashardwiredcontrol/Circuitdiagramshadtobedesigned/electricalcomponentsspecifiedandinstalled/andwiringlistscreated/Electricalcomponentsne
18、cessarytoperformaspecifictask/Ifanerrorwasmadethewireshadtobereconnectedcorrectly/Achangeinfunctionorsystemexpansionrequiredextensivecomponentchangesandrewiring/3/AdvantagesofPLCsThesame/aswellasmorecomplextasks/canbedonewithaPLC/WiringbetweendevicesandrelaycontactsisdoneinthePLCprogram/Hard-wiring/
19、thoughstillrequiredtoconnectfielddevices/islessintensive/Modifyingtheapplicationandcorrectingerrorsareeasiertohandle/ItiseasiertocreateandchangeaprograminaPLCthanitistowireandrewireacircuit/FollowingarejustafewoftheadvantagesofPLCs/(1)Smallerphysicalsizethanhard-wiresolutions/(2)Easierandfastertomak
20、echanges/(3)PLCshaveintegrateddiagnosticsandoverridefunctions/(4)Applicationscanbeimmediatelydocumented/(5)Applicationscanbeduplicatedfasterandlessexpensively/4/SiemensPLCsSiemensmakesseveralPLCproductlinesintheSIMATICS7family/Theyare/S7-200/S7-300/andS7-400/(1)S7-200TheS7-200isreferredtoasamicro-PL
21、Cbecauseofitssmallsize/TheS7-200hasabrickdesignwhichmeansthatthepowersupplyandI/Oterminalareon-board/TheS7-200canbeusedonsmaller/stand-aloneapplicationssuchaselevators/carwashes/ormixingmachines/Itcanalsobeusedonmorecomplexindustrialapplicationssuchasbottlingandpackagingmachines/(2)S7-300andS7-400Th
22、eS7-300andS7-400PLCsareusedinmorecomplexapplicationsthatsupportagreaterofI/Opoints/BothPLCsaremodularandexpandable/ThepowersupplyandI/OconsistofseparatemodulesconnectedtotheCPU/ChoosingeithertheS7-300orS7-400dependsonthecomplexityofthetaskandpossiblefutureexpansion/YourSiemenssalesrepresentativecanp
23、rovideyouwithadditionalinformationonanyoftheSiemensPLCs/5/CPUCPUisamicroprocessorsystemthatcontainsthesystemmemoryandisthePLCdecision-makingunit/TheCPUmonitorstheinputsandmakesdecisionsbasedoninstructionsheldintheprogrammemory/TheCPUperformsrelay/countingtiming/datacomparison/andsequentialoperations
24、/6/ProgrammingDevicesTheprogramiscreatedinaprogrammingdevice(PG)andthentransferredtothePLC/TheprogramfortheS7-200canbecreatedusingadedicatedSiemensSIMATICS7programmingdevice/suchasaPG720orPG740/ifSTEP7Micro/WINsoftwareisinstalled/Apersonalcomputer(PC)/withSTEP7Micro/WINinstalled/canalsobeusedasaprog
25、rammingdevicewiththeS7-200/7/SoftwareAsoftwareprogramisrequiredinordertotellthePLCwhatinstructionsitmustfollow/ProgrammingsoftwareistypicallyPLCspecific/AsoftwarepackageforonePLC/oronefamilyofPLCs/suchastheS7family/wouldnotbeusefulonotherPLCs/TheS7-200usesaWindows-basedsoftwareprogramcalledSTEP7-Micro/WIN32/ThePG720andPG740haveSTEP7-Micro/WIN32softwarepre-installed/Micro/WIN32isinstalledonapersonalcomputerinasimilarmannertoanyothercomputersoftware/8/ConnectorCablesPPI(Point-to-PointInterface)Connectorcablesarerequiredtotransferdatafromtheprogrammingdeviceto
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