毕业设计论文外文文献翻译PLC相关PLC的发展中英文对照

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的发展一、PLC概述可编程控制器是60年代末在美国首先出现的，当时叫可编程逻辑控制器PLC（ProgrammableLogicController），目的是用来取代继电器。以执行逻辑判断、计时、计数等顺序控制功能。提出PLC概念的是美国通用汽车公司。PLC的基本设计思想是把计算机功能完善、灵活、通用等优点和继电器控制系统的简单易懂、操作方便、价格便宜等优点结合起来，控制器的硬件是标准的、通用的。根据实际应用对象，将控制内容编成软件写入控制器的用户程序存储器内,使控制器和被控对象连接方便。70年代中期以后，PLC已广泛地使用微处理器作为中央处理器，输入输出模块和外围电路也都采用了中、大规模甚至超大规模的集成电路，这时的PLC已不再是仅有逻辑(Logic)判断功能，还同时具有数据处理、PID调节和数据通信功能。国际电工委员会(IEC)颁布的可编程控制器标准草案中对可编程控制器作了如下的定义：可编程控制器是一种数字运算操作的电子系统，专为在工业环境下应用而设计。它采用了可编程序的存储器，用来在其内部存储执行逻辑运算，顺序控制、定时、计数和算术运算等操作的指令，并通过数字式和模拟式的输入和输出，控制各种类型的机械或生产过程。可编程控制器及其有关外围设备，易于与工业控制系统联成一个整体，易于扩充其功能的设计。可编程控制器对用户来说，是一种无触点设备，改变程序即可改变生产工艺。目前，可编程控制器已成为工厂自动化的强有力工具，得到了广泛的普及推广应用。可编程控制器是面向用户的专用工业控制计算机，具有许多明显的特点。①可靠性高，抗干扰能力强；②编程直观、简单；③适应性好；④功能完善，接口功能强二、PLC的历史1968年，RichardE.Morley创造出了新一代工业控制装置可编程逻辑控制器(PLC),现在，PLC已经被广泛应用于工业领域，包括机械制造也、运输系统、化学过程设备、等许多其他领域。初期可编程控制器只是用一种类似于语言的软件逻辑于代替继电器硬件逻辑，并且使开发时间由6个月缩短到6天。虽然计算机控制技术已经产生，但是PLC控制因为它的高性能、成本低、并且对恶劣的环境有很强的适应能力而在工业控制的广泛应用中保持优势。而且，尽管硬件的价格在逐渐下跌，据估计，根据Frost和Sullivan对PLC市场的调查研究表明，每年销售硬件的价格要比销售PLC的价格（一千五百万）至少多出八十亿美元。PLC的创造者RichardE.Morley十分肯定的认为目前PLC市场是一个价值五十亿的工业。虽然PLC广泛应用于工业控制中，PLC控制系统的程序依然和语法有关。和软件过程一样，PLC的软件设计也以同样的方式会遇到软件错误或危机。Morley在演讲中着重强调了这个方面。如果房子建造的像软件过程一样，那么仅仅一只啄木鸟就可以摧毁文明。特别的，PLC程序要解决的实际问题是消除软件错误和减少老式梯形逻辑语言的花费。尽管PLC的硬件成本在继续下降，但是在工业控制上减少梯形逻辑的扫描时间仍然是一个问题，以至于可以用到低耗时的PLC。一般来说，和其他领域相比生产PLC的周期要短很多。例如，在实践中，VISI设计是一种有效的计算机辅助设计。PLC不需要使用目前的以软件设计为基础软件工程方法论，因为PLC程序要求对软件和硬件搜都要考虑到。因此，软件设计越来越成为花费动力。在许多的工业设计工程中，多数人力分配给了控制系统设计和安装，并且他们被要求对PLC进行程序测试和错误排除。再者，PLC控制系统不适合设计对适应性和重构有越来越多要求的生产系统。一个更深入的问题是在大规模的工程中软件越来越复杂，促使要有一个系统化的设计方法论。主题的客观性是为PLC自动控制系统建立一个系统化的软件设计方法论。这个设计方法论包括以状态转换模型为基础的精确的描述，这个转台转换模型是自动控制系统的抽象系统。方法论还包括一个逐步的设计过程，并且要设置一个设计规则，这样才能为一个成功的设计提供导向和方法。这项研究的真正目的是找到一个减少控制软件发展过程的不稳定性的方法，也就是说，减少程序和调试时间以及他们的变化，以增强自动控制系统的适应性，并且通过调整软件使得软件可以再度使用。这样的目的是为了克服目前程序策略的不足之处，而目前的程序策略是以个人软件开发者的经验为基础的。三、现今的PLC从结构上分，PLC分为固定式和模块式两种。固定式PLC包括CPU板、I/O板、显示面板、内存块、电源等，这些元素组合成一个不可拆卸的整体。模块式PLC包括CPU模块、I/O模块、内存、电源模块、底板或机架，这些模块可以按照一定规则组合配置。在使用者看来，不必要详细分析CPU的内部电路，但对各部分的工作机制还是应有足够的理解。CPU的控制器控制CPU工作，由它读取指令、解释指令及执行指令。但工作节奏由震荡信号控制。运算器用于进行数字或逻辑运算，在控制器指挥下工作。寄存器参与运算，并存储运算的中间结果，它也是在控制器指挥下工作。CPU速度和内存容量是PLC的重要参数，它们决定着PLC的工作速度，IO数量及软件容量等，因此限制着控制规模。中央处理器(CPU)是PLC控制器的大脑。通常CPU本身就是一个微控制器。起先是8位微控制器例如8051,现在发展为16位和32位微控制器。你会发现大部分由日本制造商制造的PLC中是日立和Fujicu的微控制器,西门子的微控制器多应用在欧洲的PLC中,摩托罗拉生产的微控制器则独占美国市场。CPU同样关注通信,PLC控制器,操作程序的执行,监督记忆设置的输入和输出等部分的关联性。PLC使用系统存储器（现在大部分采用闪存技术了）用于过程控制系统。除了这个操作系统之外，它还包括一个由梯形图翻译成而进制形式的用户程序。快擦型存储器（FLASHmemory）的内容只有在改变用户程序的时候可以被改变。PLC控制器比快擦型存储器使用得更早，EPROM存储器比快擦型存储器也更早，快擦型存储器必须用紫外线（UV，Ultra-VioletRay）灯擦除，并在编程器上进行编程。由于快擦型存储器技术的应用，使得这个过程大大缩短了。在应用程序开发中，通过一个串行电缆可以对程序存储器进行重新编程。用户存