畢業(yè)設(shè)計(jì)論文外文文獻(xiàn)翻譯PLC相關(guān)PLC的發(fā)展中英文對(duì)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的發(fā)展一、PLC概述可編程控制器是60年代末在美國首先出現(xiàn)的，當(dāng)時(shí)叫可編程邏輯控制器PLC（ProgrammableLogicController），目的是用來取代繼電器。以執(zhí)行邏輯判斷、計(jì)時(shí)、計(jì)數(shù)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(shè)計(jì)思想是把計(jì)算機(jī)功能完善、靈活、通用等優(yōu)點(diǎn)和繼電器控制系統(tǒng)的簡單易懂、操作方便、價(jià)格便宜等優(yōu)點(diǎn)結(jié)合起來，控制器的硬件是標(biāo)準(zhǔn)的、通用的。根據(jù)實(shí)際應(yīng)用對(duì)象，將控制內(nèi)容編成軟件寫入控制器的用戶程序存儲(chǔ)器內(nèi),使控制器和被控對(duì)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(guī)模甚至超大規(guī)模的集成電路，這時(shí)的PLC已不再是僅有邏輯(Logic)判斷功能，還同時(shí)具有數(shù)據(jù)處理、PID調(diào)節(jié)和數(shù)據(jù)通信功能。國際電工委員會(huì)(IEC)頒布的可編程控制器標(biāo)準(zhǔn)草案中對(duì)可編程控制器作了如下的定義：可編程控制器是一種數(shù)字運(yùn)算操作的電子系統(tǒng)，專為在工業(yè)環(huán)境下應(yīng)用而設(shè)計(jì)。它采用了可編程序的存儲(chǔ)器，用來在其內(nèi)部存儲(chǔ)執(zhí)行邏輯運(yùn)算，順序控制、定時(shí)、計(jì)數(shù)和算術(shù)運(yùn)算等操作的指令，并通過數(shù)字式和模擬式的輸入和輸出，控制各種類型的機(jī)械或生產(chǎn)過程?？删幊炭刂破骷捌溆嘘P(guān)外圍設(shè)備，易于與工業(yè)控制系統(tǒng)聯(lián)成一個(gè)整體，易于擴(kuò)充其功能的設(shè)計(jì)?？删幊炭刂破鲗?duì)用戶來說，是一種無觸點(diǎn)設(shè)備，改變程序即可改變生產(chǎn)工藝。目前，可編程控制器已成為工廠自動(dòng)化的強(qiáng)有力工具，得到了廣泛的普及推廣應(yīng)用?？删幊炭刂破魇敲嫦蛴脩舻膶Ｓ霉I(yè)控制計(jì)算機(jī)，具有許多明顯的特點(diǎn)。①可靠性高，抗干擾能力強(qiáng)；②編程直觀、簡單；③適應(yīng)性好；④功能完善，接口功能強(qiáng)二、PLC的歷史1968年，RichardE.Morley創(chuàng)造出了新一代工業(yè)控制裝置可編程邏輯控制器(PLC),現(xiàn)在，PLC已經(jīng)被廣泛應(yīng)用于工業(yè)領(lǐng)域，包括機(jī)械制造也、運(yùn)輸系統(tǒng)、化學(xué)過程設(shè)備、等許多其他領(lǐng)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(fā)時(shí)間由6個(gè)月縮短到6天。雖然計(jì)算機(jī)控制技術(shù)已經(jīng)產(chǎn)生，但是PLC控制因?yàn)樗母咝阅?、成本低、并且?duì)惡劣的環(huán)境有很強(qiáng)的適應(yīng)能力而在工業(yè)控制的廣泛應(yīng)用中保持優(yōu)勢(shì)。而且，盡管硬件的價(jià)格在逐漸下跌，據(jù)估計(jì)，根據(jù)Frost和Sullivan對(duì)PLC市場的調(diào)查研究表明，每年銷售硬件的價(jià)格要比銷售PLC的價(jià)格（一千五百萬）至少多出八十億美元。PLC的創(chuàng)造者RichardE.Morley十分肯定的認(rèn)為目前PLC市場是一個(gè)價(jià)值五十億的工業(yè)。雖然PLC廣泛應(yīng)用于工業(yè)控制中，PLC控制系統(tǒng)的程序依然和語法有關(guān)。和軟件過程一樣，PLC的軟件設(shè)計(jì)也以同樣的方式會(huì)遇到軟件錯(cuò)誤或危機(jī)。Morley在演講中著重強(qiáng)調(diào)了這個(gè)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(shí)際問題是消除軟件錯(cuò)誤和減少老式梯形邏輯語言的花費(fèi)。盡管PLC的硬件成本在繼續(xù)下降，但是在工業(yè)控制上減少梯形邏輯的掃描時(shí)間仍然是一個(gè)問題，以至于可以用到低耗時(shí)的PLC。一般來說，和其他領(lǐng)域相比生產(chǎn)PLC的周期要短很多。例如，在實(shí)踐中，VISI設(shè)計(jì)是一種有效的計(jì)算機(jī)輔助設(shè)計(jì)。PLC不需要使用目前的以軟件設(shè)計(jì)為基礎(chǔ)軟件工程方法論，因?yàn)镻LC程序要求對(duì)軟件和硬件搜都要考慮到。因此，軟件設(shè)計(jì)越來越成為花費(fèi)動(dòng)力。在許多的工業(yè)設(shè)計(jì)工程中，多數(shù)人力分配給了控制系統(tǒng)設(shè)計(jì)和安裝，并且他們被要求對(duì)PLC進(jìn)行程序測試和錯(cuò)誤排除。再者，PLC控制系統(tǒng)不適合設(shè)計(jì)對(duì)適應(yīng)性和重構(gòu)有越來越多要求的生產(chǎn)系統(tǒng)。一個(gè)更深入的問題是在大規(guī)模的工程中軟件越來越復(fù)雜，促使要有一個(gè)系統(tǒng)化的設(shè)計(jì)方法論。主題的客觀性是為PLC自動(dòng)控制系統(tǒng)建立一個(gè)系統(tǒng)化的軟件設(shè)計(jì)方法論。這個(gè)設(shè)計(jì)方法論包括以狀態(tài)轉(zhuǎn)換模型為基礎(chǔ)的精確的描述，這個(gè)轉(zhuǎn)臺(tái)轉(zhuǎn)換模型是自動(dòng)控制系統(tǒng)的抽象系統(tǒng)。方法論還包括一個(gè)逐步的設(shè)計(jì)過程，并且要設(shè)置一個(gè)設(shè)計(jì)規(guī)則，這樣才能為一個(gè)成功的設(shè)計(jì)提供導(dǎo)向和方法。這項(xiàng)研究的真正目的是找到一個(gè)減少控制軟件發(fā)展過程的不穩(wěn)定性的方法，也就是說，減少程序和調(diào)試時(shí)間以及他們的變化，以增強(qiáng)自動(dòng)控制系統(tǒng)的適應(yīng)性，并且通過調(diào)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(gè)人軟件開發(fā)者的經(jīng)驗(yàn)為基礎(chǔ)的。三、現(xiàn)今的PLC從結(jié)構(gòu)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(nèi)存塊、電源等，這些元素組合成一個(gè)不可拆卸的整體。模塊式PLC包括CPU模塊、I/O模塊、內(nèi)存、電源模塊、底板或機(jī)架，這些模塊可以按照一定規(guī)則組合配置。在使用者看來，不必要詳細(xì)分析CPU的內(nèi)部電路，但對(duì)各部分的工作機(jī)制還是應(yīng)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(zhí)行指令。但工作節(jié)奏由震蕩信號(hào)控制。運(yùn)算器用于進(jìn)行數(shù)字或邏輯運(yùn)算，在控制器指揮下工作。寄存器參與運(yùn)算，并存儲(chǔ)運(yùn)算的中間結(jié)果，它也是在控制器指揮下工作。CPU速度和內(nèi)存容量是PLC的重要參數(shù)，它們決定著PLC的工作速度，IO數(shù)量及軟件容量等，因此限制著控制規(guī)模。中央處理器(CPU)是PLC控制器的大腦。通常CPU本身就是一個(gè)微控制器。起先是8位微控制器例如8051,現(xiàn)在發(fā)展為16位和32位微控制器。你會(huì)發(fā)現(xiàn)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(yīng)用在歐洲的PLC中,摩托羅拉生產(chǎn)的微控制器則獨(dú)占美國市場。CPU同樣關(guān)注通信,PLC控制器,操作程序的執(zhí)行,監(jiān)督記憶設(shè)置的輸入和輸出等部分的關(guān)聯(lián)性。PLC使用系統(tǒng)存儲(chǔ)器（現(xiàn)在大部分采用閃存技術(shù)了）用于過程控制系統(tǒng)。除了這個(gè)操作系統(tǒng)之外，它還包括一個(gè)由梯形圖翻譯成而進(jìn)制形式的用戶程序?？觳列痛鎯?chǔ)器（FLASHmemory）的內(nèi)容只有在改變用戶程序的時(shí)候可以被改變。PLC控制器比快擦型存儲(chǔ)器使用得更早，EPROM存儲(chǔ)器比快擦型存儲(chǔ)器也更早，快擦型存儲(chǔ)器必須用紫外線（UV，Ultra-VioletRay）燈擦除，并在編程器上進(jìn)行編程。由于快擦型存儲(chǔ)器技術(shù)的應(yīng)用，使得這個(gè)過程大大縮短了。在應(yīng)用程序開發(fā)中，通過一個(gè)串行電纜可以對(duì)程序存儲(chǔ)器進(jìn)行重新編程。用戶存