PLCdevelopment1、PLCoverviewProgrammablecontrolleristhefirstinthelate1960sintheUnitedStthencalledPlcprogrammablelogiccontroller(ProgrammableLogicControllerisusedtoreplacerelays.Fortheimplementationofthelogicaljudgment,timing,sequencenumber,andothercontrolfunctions.TheconceptispresentPlcGeneralMotorsCorporation.Plcandthebasicdesignisthecomputerfunctionalimprovements,flexible,genericandotheradvantagesandrelaycontrolsystemsimpleandeasytooperate,suchastheadvantagesofcheappricescombinedcontrollerhardwareisstandardandoverall.Accordingtotpracticalapplicationoftargetsoftwareinordertocontrolthecontentoftheuserproceduresmemorycontroller,thecontrollerandconnectingtheaccuseconvenienttarget.Inthemid-1970s,thePlchasbeenwidelyusedasacentralprocessingunitmicroprocessor,importexportmoduleandtheexternalcircuitsareuslarge-scaleintegratedcircuitsevenwhenthePlcisnolongertheonlylo(IC)judgmentfunctionsalsohavedataprocessing,PIDconditioninganddatcommunicationsfunctions.InternationaElectrotechnicalCommission(IEC)standardspromulgatedprogrammablecontrollerforprogrammablecontrollerdraftmadethefollowingdefinition:programmablecontrollerisadigitalelectronicomputersoperatingsystem,specificallyforapplicationsintheindustrialdesignenvironment.Itusedprogrammablememory,usedtoimplementlogicintheirinternalstorageoperations,sequencecontrol,timcountingandarithmeticoperations,suchasoperatinginstructions,andthrodigitalandanaloginputandoutput,thecontrolofvarioustypesofmachiorproductionprocesses.Programmablecontrollerandrelatedperipherals,aindustrialcontrolsystemseasilylinkedtoformawhole,toexpanditsfunctionaldesign.Programmablecontrollerfortheuser,isnon-contactequipment,theprocedurescanbechangedtochangeproductionprocesses.Theprogrammablecontrollerhasbecomeapowerfultoolforfactoryautomation,widelypopularreplication.Programmablecontrollerisuser-orientedindustrdedicatedcontrolcomputer,withmanydistinctivefeatures.First,highreliability,anti-interferencecapability;Second，programmingvisual,simple;Third,adaptabilitygood;Fourth,functionalimprovements,strongfunctionalinterface.2、HistoryofPLCProgrammableLogicControllers(PLC),acomputingdeviceinventedbyRichardE.Morleyin1968,havebeenwidelyusedinindustryincludingmanufacturingsystems,transportationsystems,chemicalprocessfacilities,manyothers.Atthattime,thePLCreplacedthehardwiredlogicwithsoft-wiredlogicorso-calledrelayladderlogic(RLL),aprogramminglanguavisuallyresemblingthehardwiredlogic,andreducedtherebytheconfiguratitimefrom6monthsdownto6days[MoodyandMorley,1999].AlthoughPCbasedcontrolhasstartedtocomeintoplace,PLCbasedcontrolwillremainthetechniquetowhichthemajorityofindustrialapplicationswilladhereduetoitshigherperformance,lowerprice,andsuperiorreliabilityinharshenvironments.Moreover,accordingtoastudythePLCmarketofFrostandSullivan[1995],anincreaseoftheannualsalvolumeto15millionPLCsperyearwiththehardwarevalueofmorethan8billionUSdollarshasbeenpredicted,thoughthepricesofcomputinghardwaissteadilydropping.TheinventorofthePLC,RichardEMorley,fairlyconsidersthePLCmarketasa5-billionindustryatthepresenttime.ThoughPLCsarewidelyusedinindustrialpractice,theprogrammingofPLCbasedcontrolsystemsisstillverymuchrelyingontrial-and-error.Asoftwareengineering,PLCsoftwaredesignisfacingthesoftwaredilemmaorcrisisinasimilarway.Morleyhimselfemphasizedthisaspectmostforcefubyindicating.Ifhouseswerebuiltlikesoftwareprojects,asinglewoodpeckercoulddestroycivilization.”Particularly,practicalproblemsinPLCprogrammingaretoeliminatesoftwarebugsandtoreducethemaintenancecostsofoldladderlogicprograThoughthehardwarecostsofPLCsaredroppingcontinuously,reducingthescantimeoftheladderlogicisstillanissueinindustrysothatlow-coscanbeused.Ingeneral,theproductivityingeneratingPLCisfarbehindcomparedotherdomains,forinstance,VLSIdesign,whereefficientcomputeraideddesigntoolsareinpractice.ExistentsoftwareengineeringmethodologiesarenotnecessarilyapplicabletothePLCbasedsoftwaredesignbecausePLC-programmingrequiresasimultaneousconsiderationofhardwareandsoftware.Thesoftwaredesignbecomes,thereby,moreandmorethemajorcostdriver.Inmanyindustrialdesignprojects,morethanofthemanpowerallocaforthecontrolsystemdesignandinstallationisscheduledfortestinganddebuggingPLCprograms.Inaddition,currentPLCbasedcontrolsystemsarenotproperlydesignedtosupportthegrowingdemandforflexibilityandreconfigurabilityofmanufacturingsystems.Afurtherproblem,impellingtheneedforasystematdesignmethodology,istheincreasingsoftwarecomplexityinlarge-scaleprojects.TheobjectiveofthisthesisistodevelopasystematicsoftwaredesignmethodologyforPLCoperatedautomationsystems.Thedesignmethodologyinvolveshigh-leveldescriptionbasedonstatetransitionmodelsthattreatautomationcontrolsystemsasdiscreteeventsystems,astepwisedesignprocess,andsetofdesignrulesprovidingguidanceandmeasurementstoachieveasuccessfuldesign.Thetangibleoutcomeofthisresearchistofiwaytoreducetheuncertaintyinmanagingthecontrolsoftwaredevelopmentprocess,thatis,reducingprogramminganddebuggingtimeandtheirvariatioincreasingflexibilityoftheautomationsystems,andenablingsoftwarereusabilitythroughmodularity.Thegoalistoovercomeshortcomingsofcurrentprogrammingstrategiesthatarebasedontheexperienceoftheindividualsoftwaredeveloper.3、nowofPLCFromthestructureisdividedintofixedPLCandModulePLC,thetwokindsofPLCincludingCPUboard,I/Oboard,displaypanel,memoryblock,power,theseelementsintoadonotremoveoverall.ModuletypePLCincludingCPUmodule,I/Omodules,memory,thepowermodules,bottomoraframe,thesemodulescanbeaccordingtocertainrulescombinationconfiguration.Intheuserview,adetailedanalysisoftheCPU'sinternalunnecessary,workingmechanismofeverypartofthecircuit.TheCPUcontrolworks,byireadsCPUinstruction,interpretstheinstructionandexecutesinstructionsthepaceofworkbyshocksignalcontrol.Unitworkunderthecontrollercommandusedinadigitalorlogicoperations.Incomputingandstorageregisterofcomputationresult,itisamongthecontrollercommandandwork.CPUspeedandmemorycapacityistheimportantparametersofPLC.ItsdeterminesthePLCspeedofwork,IOPLCnumberandsoftwarecapacity,solimitstocontrolsize.CentralProcessingUnit(CPU)isthebrainofaPLCcontroller.CPUitseisusuallyoneofthemicrocontrollers.Aforetimethesewere8-bitmicrocontrollersuchas8051,andnowtheseare16-and32-bitmicrocontrollers.Unspokenruleisthatyou’llfindmostlyHitachiandFujicumicrocontrollersinPLCcontrollersbyJapanesemakers,SiemensinEuropeancontrollers,andMotorolamicrocontrollersinAmericanones.CPUalsotakecareofcommunication,interconnectednessamongotherpartsofPLCcontrollers,programexecution,memoryoperation,overseeinginputandsettingupofanoutput.Systemmemory(todaymostlyimplementedinFLASHtechnology)isusedbyaPLCforaprocesscontrolsystem.Asideform.thisoperatingsystitalsocontainsauserprogramtranslatedformaladderdiagramtoabinaryform.FLASHmemorycontentscanbechangedonlyincasewhereuserprogramisbeingchanged.PLCcontrollerswereusedearlierinsteadofPLASHmemoryandhavehadEPROMmemoryinsteadofFLASHmemorywhichhadtobeerasedwithUVlampandprogrammedonprogrammers.WiththeuseofFLASHtechnologythisprocesswasgreatlyshortened.Reprogrammingaprogrammemoryisdonethroughaserialcableinaprogramforapplicationdevelopment.Usermemoryisdividedintoblockshavingspecialfunctions.Somepartsofamemoryareusedforstoringinputandoutputstatus.Therealstatusoinputisstoredeitheras“1”oras“0”inaspecificmemorybit/eachinputoroutputhasonecorrespondingbitinmemory.Otherpartsofmemoryareusedtstorevariablecontentsforvariablesusedinusedprogram.Forexample,tvalue,orcountervaluewouldbestoredinthispartofthememory.PLCcontrollercanbereprogrammedthroughacomputer(usualway),butalsothroughmanualprogrammers(consoles).ThispracticallymeansthateacPLCcontrollercanprogrammedthroughacomputerifyouhavethesoftwareneededforprogramming.Today’stransmissioncomputersareidealforreprogrammingaPLCcontrollerinfactoryitself.Thisisofgreatimportancindustry.Oncethesystemiscorrected,itisalsoimportanttoreadtherightprogramintoaPLCagain.ItisalsogoodtocheckfromtimetotimewhethprograminaPLChasnotchanged.Thishelpstoavoidhazardoussituationsfactoryrooms(someautomakershaveestablishedcommunicationnetworkswhichregularlycheckprogramsinPLCcontrollerstoensureexecutiononlyogoodprograms).AlmosteveryprogramforprogrammingaPLCcontrollerpossessesvarioususefuloptionssuchas:forcedswitchingonandoffofthesysteminput/outputs(I/Olines),programfollowupinrealtimeaswellasdocumentingadiagram.Thisdocumentingisnecessarytounderstandanddefinefailuresandmalfunctions.Programmercanaddremarks,namesofinputoroutputdevices,andcommentsthatcanbeusefulwhenfindingerrors,orwithsystemmaintenance.Addingcommentsandremarksenablesanytechnician(andnotjustapersonwhodevelopedthesystem)tounderstandaladderdiagramrightaway.Commentsandremarkscanevenquotepreciselypartnumbersifreplacementswouldbeneeded.Thiswouldspeeduparepairoanyproblemsthatcomeupduetobadparts.Theoldwaywassuchthatapersonwhodevelopedasystemhadprotectionontheprogram,sonobodyasidefromthispersoncouldunderstandhowitwasdone.Correctlydocumentedladderdiagramallowsanytechniciantounderstandthoroughlyhowsystemfunctions.Electricalsupplyisusedinbringingelectricalenergytocentralproceunit.MostPLCcontrollersworkeitherat24VDCor220VAC.OnsomePLCcontrollersyou’llfindelectricalsupplyasaseparatemodule.ThoseareubiggerPLCcontrollers,whilesmallandmediumseriesalreadycontainthesupplymodule.UserhastodeterminehowmuchcurrenttotakefromI/OmoduletoensurethatelectricalsupplyprovidesappropriateamountofcurreDifferenttypesofmodulesusedifferentamountsofelectricalcurrent.ThiselectricalsupplyisusuallynotusedtostartexternalinputoroUserhastoprovideseparatesuppliesinstartingPLCcontrollerinputsbecthenyoucanensuresocalled“pure”supplyforthePLCcontroller.Withsupplywemeansupplywhereindustrialenvironmentcannotaffectitdamagingly.SomeofthesmallerPLCcontrollerssupplytheirinputswithvoltagefromasmallsupplysourcealreadyincorporatedintoaPLC.4、PLCdesigncriteriaAsystematicapproachtodesigningPLCsoftwarecanovercomedeficienciesinthetraditionalwayofprogrammingmanufacturingcontrolsystems,andcanhavewideramificationsinseveralindustrialapplications.Automationcontrolsystemsaremodeledbyformallanguagesor,equivalently,bystatemachines.Formalrepresentationsprovideahigh-leveldescriptionthebehaviorofthesystemtobecontrolled.Statemachinescanbeanalyticevaluatedastowhetherornottheymeetthedesiredgoals.Secondly,astatemachinedescriptionprovidesastructuredrepresentationtoconveythelogirequirementsandconstraintssuchasdetailedsafetyrules.Thirdly,well-decontrolsystemsdesignoutcomesareconducivetoautomaticcodegenerationAnabilitytoproducecontrolsoftwareexecutableoncommercialdistinctlocontrollerscanreduceprogramminglead-timeandlaborcost.Inparticular,thesisisrelevantwithrespecttothefollowingaspects.Inmodernmanufacturing,systemsarecharacterizedbyproductandprocessinnovation,becomecustomer-drivenandthushavetorespondquicklytochangingsystemrequirements.Amajorchallengeisthereforetoprovideenablingtechnologiesthatcaneconomicallyreconfigureautomationcontrolsystemsinresponsetochangingneedsandnewopportunities.Designandoperationalknowledgecanbereusedinreal-time,therefore,givingasignificantcompetitiveedgeinindustrialpractice.Studieshaveshownthatprogrammingmethodologiesinautomationsystemshavenotbeenabletomatchrapidincreaseinuseofcomputingresources.Forinstance,theprogrammingofPLCsstillreliesonaconventioprogrammingstylewithladderlogicdiagrams.Asaresult,thedelaysandresourcesinprogrammingareamajorstumblingstonefortheprogressofmanufacturingindustry.Testinganddebuggingmayconsumeover50%ofthemanpowerallocatedforthePLCprogramdesign.Standards[IEC60848,1999;IEC-61131-3,1993;IEC61499,1998;ISO15745-1,1999]havebeenformedtofixanddisseminatestate-of-the-artdesignmethods,buttheynormallycannotparticipateinadvancingtheknowledgeofefficientprogramandsystedesign.Asystematicapproachwillincreasethelevelofdesignautomationthroughreusingexistingsoftwarecomponents,andwillprovidemethodstomakelarge-scalesystemdesignmanageable.Likewise,itwillimprovesoftwarequalityandreliabilityandwillberelevanttosystemshighsecuritystandards,especiallythosehavinghazardousimpactontheenvironmentsucasairportcontrol,andpublicrailroads.Thesoftwareindustryisregardedasaperformancedestructorandcomplexitygenerator.Steadilyshrinkinghardwarepricesspoilstheneedforsoftwareperformanceintermsofcodeoptimizationandefficiency.Theresuisthatmassiveandlessefficientsoftwarecodeononehandoutpacestheginhardwareperformanceontheotherhand.Secondly,softwareproliferatesintocomplexityofunmanageabledimensions;softwareredesignandmaintenance-essentialinmodernautomationsystems-becomesnearlyimpossible.Particularly,PLCprogramshaveevolvedfromacouplelinesofcode25yearsagotothousandsoflinesofcodewithasimilarnumberof1points.Increasedsafety,forinstancenewpoliciesonfireprotection,andtheflexibilityofmodernautomationsystemsaddcomplexitytotheprogramdesignprocess.Consequently,thelife-cyclecostofsoftwareisapermanengrowingfractionofthetotalcost.80-90%ofthesecostsaregoingintosoftwaremaintenance,debugging,adaptationandexpansiontomeetchangingneeds.Today,theprimaryfocusofmostdesignresearchisbasedonmechanicalorelectricalproducts.Oneoftheby-productsofthisproposedresearchistoenhanceourfundamentalunderstandingofdesigntheoryandmethodologybyextendingittothefieldofengineeringsystemsdesign.Asystemdesigntheforlarge-scaleandcomplexsystemisnotyetfullydeveloped.Particularlyquestionofhowtosimplifyacomplicatedorcomplexdesigntaskhasnotbeetackledinascientificway.Furthermore,buildingabridgebetweendesigntheoryandthelatestepistemologicaloutcomesofformalrepresentationsincomputersciencesandoperationsresearch,suchasdiscreteeventsystemmodeling,canadvancefuturedevelopmentinengineeringdesign.Fromalogicalperspective,PLCsoftwaredesignissimilartothehardwaredesignofintegratedcircuits.ModernVLSIdesignsareextremelycomplexwithseveralmillionpartsandaproductdevelopmenttimeof3year[Whitney,1996].Thedesignprocessisnormallyseparatedintoacomponentdesignandasystemdesignstage.Atcomponentdesignstage,singlefunctioaredesignedandverified.Atsystemdesignstage,componentsareaggregateandthewholesystembehaviorandfunctionalityistestedthroughsimulatiIngeneral,acompleteverificationisimpossible.Hence,asystematicapproasexemplifiedforthePLCprogramdesignmayimpactthelogicalhardwaredesign.5、AK1703ACPFollowingtheprincipleofourproductdevelopment,AK1703ACPhashighfunctionalityandflexibility,throughtheimplementationofinnovatireliabletechnologies,onthestablebasisofareliableproductplatform.Forthis,thesystemconceptACP(Automation,ControlandProtection)createsthetechnologicalpreconditions.Balancedfunctionalitypermitstheflexiblecombinationofautomation,telecontrolandcommunicationtasks.Complementedwiththescalableperformanceandvariousredundancyconfigurations,anoptimaladaptationtotherespectiverequirementsoftheprocessisachieved.AK1703ACPisthusperfectlysuitableforautomationwithintegratedtelecontroltechnologyas:TelecontrolsubstationorcentraldeviceAutomationunitwithautonomousfunctionalgroupsDatanode,stationcontroldevice,front-endorgatewayWithlocalorremoteperipheralsForrearpanelinstallationor19inchassemblyBranch-neutralproduct,thereforeversatilefieldsofapplicationandproductstabilityVersatilecommunicationEasyengineeringPlug&playforsparepartsOpensystemarchitectureScalableredundancyTheintelligentterminal-TM1703TheBaseUnitAK1703ACPwithPeripheralElementshasonebasicsystemelementCP-2010/CPC25(Mastercontrolelement)andCP-2012/PCCE25(Processingandcommunicationelement),onebuslinewithmax.16peripheralelementscanbeconnected.CP-2010/CPC25FeaturesandFunctionsSystemFunctions:Centralelement,coordinatingallsystemservicesCentralhubfunctionforallconnectedbasicsystemelementsTimemanagementCentralclockoftheautomationunitSettingandkeepingtheownclock’stimewitharesolutionof10msSynchronizationviasiredcommunicationviaLANorlocalRedundancyVotingandchange-overforredundantprocessingandcommunicationelementsoftheownautomationunitSupportsvotingandchange-overbyanexternalSCA-RSredundancySwitchSupportsapplicationvotingandchange-overbyanexternalsystem,e.g.controlsystemSATTOLLBOX||connectionStoringfirmwareandparametersonaFlashCardCommunication:CommunicationviainstallableprotocolelementstoanysuperiororsubordinateautomationunitAutomaticdataflowroutingPrioritybaseddatatransmission(prioritycontrol)Owncircularbufferandprocessimageforeachconnectedstation(datkeeping)RedundantcommunicationroutesCommunicationwithredundantremotestationsSpecialapplicationspecificfunctionsfordial-uptrafficTestifstationsarereachableProcessPeripherals:Transmissionofspontaneousinformationobjectsfromandtoperipheralelements,viatheserialAx1703peripheralbusFunctionsforAutomation:Open-/closed-loopcontrolfunctionfortheexecutionoffreelydefinauserprogramswhicharecreatedwithCAEXplusaccordingtoIEC61131-3,e.g.usingfunctiondiagramtechnology512KBforuserprogramApprox50.000variablesandsignals,2.000ofthemretainedCycleof10msoramultiphasethereofOnlinetestLoadablewithoutserviceinterruptionRedundantopen-/closed-loopcontrolfunctionsSynchronizationviaredundancylinkTransmissionofperiodicprocessinformationbetweentheOpen-/closed-loopcontrolfunctionandtheperipheralelements,viatheseAx1703peripheralbus6、SIEMENSPLCSIMATICS7-300seriesPLCappliedtoallwalksoflifeandvariousoccasionsinthedetection,monitoringandcontrolofautomation,itspowerboththeindependentoperationof,orconnectedtoanetworkabletoachiecomplexcontrol.Thephotoelectricproductswithisolation,highelectromagneticcompatibility;havehighindustrialapplicability,allowingtheambienttemperatureof60℃;hasstronganti-jammingandanti-vibrationandimpactresistance,soinaharshworkingenvironmenthasbeenwidelyApplications.IalsomeanfreedomofcommunicationS7-300typePLC'saveryuniquefeature,whichallowsS7-300-PLCcandealopenlywithanyothercommunicationsequipment,communicationscontroller,orPLCS7-300typecanbedefinedbytheuser'sownCommunicationsprotocol(oftheagreementASCII),thebaudrateto1.5Mbit/s(adjustable).Sothatcangreatlyinthescopeofcommunicationssothatthecontrolsystemconfigurationmoreflexibleandconvenient.Ofanykindwithaserialinterfaceperipherals,suprintersorbarcodereaders,Drives,amodem(Modem),thetopPC-connected,andsocanbeused.Userscanprogramtodevelopcommunicationprotocols,theexchangeofdata(forexample:ASCIIcharactercode),RS232interfaceswiththeequipmentcanalsobeusedPC/PPIcablelinkingthefreecommunicationcommunications.WhenthePCoffline,underthecontrolofthenextcrew,thewholesystecanoperatenormally.PCthatisbycontrolcentre,mainlybythePCandlaserprintercomponents,usingSIMATICWINCCsoftwareplatform,theall-Chineseinterface,friendlyman-machinedialogue.ManagersandoperatorscanbeobservedthroughaPC,showninthevariouskindsofinformationtounderstandthepresentandpasttheice-storageoperationoftheautomaticcontrolsystemandalltheparameters,andthroughthemousetoprintequipmentmanagementandimplementationtasks.WINCCsoftwareinthefieldofautomationcanbeusedforalltheoperators’controlandmonitoringtasks.Canbecontrolledintheprocessoeventsclearlyshow,andshowsthecurrentstatusandorderrecords,therecordeddatacanshowallorselectsummaryform,ormayberequiredforediting,printingandoutputstatementsandtrends.WINCCabletocontrolthecriticalsituationintheearlystagesofthereport,andthesignalcanbedisplayedonthescreen,canalsousesoundtfelt.ItsupportedbyonlinehelpandoperationalguidelinestoeliminatefWINCCaworkstationcanbedevotedtotheprocesscontroltotheprocesssthatimportantinformationnotisshielded.Software-assistedoperationstraensuresthattheprocesswasnotillegaltovisitandtoprovidefornon-indenvironmentinthewrongoperation.WINCCisMICRSOFTWINDOWS98orWINDOWSNT4.0operatingsystem,runningonaPCobject-orientedclass32-bitapplication,OLEthrouthewindowandODBCstandardmechanism,anideals partnertoenterthecommunicationsworldWINDOWS,itcanbeeasilyWINCCTointegrateacompany-widedataprocessingsystem.7、CommunicationsCommunicationsarevitaltoanindividualautomationcellandtotheautomatedfactoryasawhole.We'veheardalotaboutMAPinthelastfewyears,andalotofcompanieshavejumpedonthebandwagon.Many,howeverweredisappointedwhenafully-definedandcompletedMAPspecificationdidn’tappearimmediately.SaysLarryKumara:”Rightnow,MAPisstillamovingtargetforthemanufacturersspecificationthatisnotfinal.Presentexample,peopleareintroducingproductstomeettheMAP2.1standard.Yet2.1-basedproductswillbeobsoletewhenthenewstandardforMAP,3.0isintroduced.”Becauseofthis,manyPLCvendorsareholdingoffonfullMAPimplementations.Omron,forexample,hasanongoingMAP-compatibilityprogram,butFrankNewborn,vicepresidentofOmron’sIndustrialDivision,reportsthatbecauseofthelackofafirmdefinition,Omron'sPLCsdon'tyettalktoMAP.Sinceit’sunlikelythatanindividualPLCwouldtalktobroadbandMAanyway,makersareconcentratingnproprietarynetworks.AccordingtoSalProvanzano,usersfearthatiftheydogetonboardandvendorswithdrawfrMAP,theyallpulsewidthmodulationcontrolsystembetheonesleftholdingcommunicationsstructurethat’snotsupported.PLC的發展一、PLC概述可編程控制器是60年代末在美國首先出現的，當時叫可編程邏輯控制器PLC（ProgrammableLogicController），目的是用來取代繼電器。以執行邏輯判斷、計時、計數等順序控制功能。提出PLC概念的是美國通用汽車公司。PLC的基本設計思想是把計算機功能完善、靈活、通用等優點和繼電器控制系統的簡單易懂、操作方便、價格便宜等優點結合起來，控制器的硬件是標準的、通用的。根據實際應用對象，將控制內容編成軟件寫入控制器的用戶程序存儲器內,使控制器和被控對象連接方便。70年代中期以后，PLC已廣泛地使用微處理器作為中央處理器，輸入輸出模塊和外圍電路也都采用了中、大規模甚至超大規模的集成電路，這時的PLC已不再是僅有邏輯(Logic)判斷功能，還同時具有數據處理、PID調節和數據通信功能。國際電工委員會(IEC)頒布的可編程控制器標準草案中對可編程控制器作了如下的定義：可編程控制器是一種數字運算操作的電子系統，專為在工業環境下應用而設計。它采用了可編程序的存儲器，用來在其內部存儲執行邏輯運算，順序控制、定時、計數和算術運算等操作的指令，并通過數字式和模擬式的輸入和輸出，控制各種類型的機械或生產過程。可編程控制器及其有關外圍設備，易于與工業控制系統聯成一個整體，易于擴充其功能的設計。可編程控制器對用戶來說，是一種無觸點設備，改變程序即可改變生產工藝。目前，可編程控制器已成為工廠自動化的強有力工具，得到了廣泛的普及推廣應用。可編程控制器是面向用戶的專用工業控制計算機，具有許多明顯的特點。①可靠性高，抗干擾能力強；②編程直觀、簡單；③適應性好；④功能完善，接口功能強二、PLC的歷史1968年，RichardE.Morley創造出了新一代工業控制裝置可編程邏輯控制器(PLC),現在，PLC已經被廣泛應用于工業領域，包括機械制造也、運輸系統、化學過程設備、等許多其他領域。初期可編程控制器只是用一種類似于語言的軟件邏輯于代替繼電器硬件邏輯，并且使開發時間由6個月縮短到6天。雖然計算機控制技術已經產生，但是PLC控制因為它的高性能、成本低、并且對惡劣的環境有很強的適應能力而在工業控制的廣泛應用中保持優勢。而且，盡管硬件的價格在逐漸下跌，據估計，根據Frost和Sullivan對PLC市場的調查研究表明，每年銷售硬件的價格要比銷售PLC的價格（一千五百萬）至少多出八十億美元。PLC的創造者RichardE.Morley十分肯定的認為目前PLC市場是一個價值五十億的工業。雖然PLC廣泛應用于工業控制中，PLC控制系統的程序依然和語法有關。和軟件過程一樣，PLC的軟件設計也以同樣的方式會遇到軟件錯誤或危機。Morley在演講中著重強調了這個方面。如果房子建造的像軟件過程一樣，那么僅僅一只啄木鳥就可以摧毀文明。特別的，PLC程序要解決的實際問題是消除軟件錯誤和減少老式梯形邏輯語言的花費。盡管PLC的硬件成本在繼續下降，但是在工業控制上減少梯形邏輯的掃描時間仍然是一個問題，以至于可以用到低耗時的PLC。一般來說，和其他領域相比生產PLC的周期要短很多。例如，在實踐中，VISI設計是一種有效的計算機輔助設計。PLC不需要使用目前的以軟件設計為基礎軟件工程方法論，因為PLC程序要求對軟件和硬件搜都要考慮到。因此，軟件設計越來越成為花費動力。在許多的工業設計工程中，多數人力分配給了控制系統設計和安裝，并且他們被要求對PLC進行程序測試和錯誤排除。再者，PLC控制系統不適合設計對適應性和重構有越來越多要求的生產系統。一個更深入的問題是在大規模的工程中軟件越來越復雜，促使要有一個系統化的設計方法論。主題的客觀性是為PLC自動控制系統建立一個系統化的軟件設計方法論。這個設計方法論包括以狀態轉換模型為基礎的精確的描述，這個轉臺轉換模型是自動控制系統的抽象系統。方法論還包括一個逐步的設計過程，并且要設置一個設計規則，這樣才能為一個成功的設計提供導向和方法。這項研究的真正目的是找到一個減少控制軟件發展過程的不穩定性的方法，也就是說，減少程序和調試時間以及他們的變化，以增強自動控制系統的適應性，并且通過調整軟件使得軟件可以再度使用。這樣的目的是為了克服目前程序策略的不足之處，而目前的程序策略是以個人軟件開發者的經驗為基礎的。三、現今的PLC從結構上分，PLC分為固定式和模塊式兩種。固定式PLC包括CPU板、I/O板、顯示面板、內存塊、電源等，這些元素組合成一個不可拆卸的整體。模塊式PLC包括CPU模塊、I/O模塊、內存、電源模塊、底板或機架，這些模塊可以按照一定規則組合配置。在使用者看來，不必要詳細分析CPU的內部電路，但對各部分的工作機制還是應有足夠的理解。CPU的控制器控制CPU工作，由它讀取指令、解釋指令及執行指令。但工作節奏由震蕩信號控制。運算器用于進行數字或邏輯運算，在控制器指揮下工作。寄存器參與運算，并存儲運算的中間結果，它也是在控制器指揮下工作。CPU速度和內存容量是PLC的重要參數，它們決定著PLC的工作速度，IO數量及軟件容量等，因此限制著控制規模。中央處理器(CPU)是PLC控制器的大腦。通常CPU本身就是一個微控制器。起先是8位微控制器例如8051,現在發展為16位和32位微控制器。你會發現大部分由日本制造商制造的PLC中是日立和Fujicu的微控制器,西門子的微控制器多應用在歐洲的PLC中,摩托羅拉生產的微控制器則獨占美國市場。CPU同樣關注通信,PLC控制器,操作程序的執行,監督記憶設置的輸入和輸出等部分的關聯性。PLC使用系統存儲器（現在大部分采用閃存技術了）用于過程控制系統。除了這個操作系統之外，它還包括一個由梯形圖翻譯成而進制形式的用戶程序。快擦型存儲器（FLASHmemory）的內容只有在改變用戶程序的時候可以被改變。PLC控制器比快擦型存儲器使用得更早，EPROM存儲器比快擦型存儲器也更早，快擦型存儲器必須用紫外線（UV，Ultra-VioletRay）燈擦除，并在編程器上進行編程。由于快擦型存儲器技術的應用，使得這個過程大大縮短了。在應用程序開發中，通過一個串行電纜可以對程序存儲器進行重新編程。用戶存