文献翻译——PLC控制系统设计的要点

第1页外文文献资料PLCcontrolsystemdesignelementsOriginally,thePLCwasrepresentedbytheacronymPC.Therewassomeconfusionwithusingthisacronymasitiscommonlyacceptedtorepresentpersonalcomputer.Therefore,PLCisnowcommonlyacceptedtomeanprogrammablelogiccontoller.APLCisauser-friendly,microprocessor-basedspecializedcomputerthatcarriesoutcontrolfunctionsofmanytypesandcomplexity.Itspurposeistomonitorcrucialprocessparametersandadjustprocessoperationsaccordingly.Itcanbeprogrammed,controlled,andoperatedbyapersonunskilledinoperatingcomputer.Essentially,aPLCsoperatordrawsthelinesanddevicesofladderdiagramswithakeyboardontoadisplayscreen.Theresultingdrawingisconvertedintocomputermachinelanguageandrunasauserprogram.Thecomputertakestheplaceofmuchoftheexternalwiringrequiredforcontrolofaprocess.ThePLCwilloperateanysystemthathasoutputdevicesthatgoonandoff(knownasdiscrete,ordigital,outputs).Itcanalsooperateanysystemwithvariable(analog)outputs.ThePLCcanbeoperatedontheinputsidebyon-offdevices(discrete,ordigital)orbyvariable(analog)inputdevices.Today,thebigunitgrowthinthePLCisatthelowend-wheresmallkeepsgettingsmaller.WhenafewyearsagothemicroPLCenteredthemarket,somethatthesedeviceshad“bottomedout”.Now,nanoPLC-generallydefinedasthosewith16orfewerI/O-arespreading.Somecanfitintoyourshirtpocket,beingnolargerthanadeckofcardsandatthetimeofthiswriting,PLCDirectplantstointroduceaPLCthesizeofaboxofTic-Taccandythatwillincludemanyfeaturesofcurrentmicromodels.Atheart,thePLCisanindustrializedcomputerprogrammedwithhighlyspecializedlanguages,anditcontinuestobenefitfromtechnologicaladvancesinthecomputerandinformationtechnologyworlds.Themostprominentofwhichisminiaturizationandcommunications.TheShrinkingPLC第2页WhenthePLCwasfirstintroduced,itssizewasamajorimprovement-relativetothehundredsofhard-wiredrelaysandtimersitreplaced.AtypicalunithousingaCPUandI/Owasroughlythesizeofa19televisionset.Throughthe1980sandearly1990s,modularPLCcontinuedtoshrinkinfootprintwhileincreasingincapabilitiesandperformance(seeDiagram1fortypicalmodularPLCconfiguration).Inrecentyears,smallerPLChasbeenintroducedinthenanoandmicroclassesthatofferfeaturespreviouslyfoundonlyinlargerPLC.ThishasmadespecifyingalargerPLCjustforadditionalfeaturesorperformance,andnotincreasedI/Ocount,unnecessary,aseventhoseinthenanoclassarecapableofEthernetcommunication,motioncontrol,on-boardPIDwithauto-tune,remoteconnectivityandmore.PLCisalsonowwell-equippedtoreplacestand-aloneprocesscontrollersinmanyapplications,duetotheirabilitytoperformfunctionsofmotioncontrol,dataacquisition,RTU(remotetelemetryunit)andevensomeintegratedHMI(humanmachineinterface)functions.Previously,thesefunctionsoftenrequiredtheirownpurpose-builtcontrollersandsoftware,plusaseparatePLCforthediscretecontrolandinterlocking.TheGreatCommunicatorPossiblythemostsignificantchangeinrecentyearsliesinthecommunicationsarena.Inthe1970scommunicationsprotocolallowedPLCtocommunicateoverstandardcabling.ThistranslatestoanabilitytoplacePLCincloserproximitytorealworlddevicesandcommunicatebacktoothersystemcontrolsinamainpanel.Inthepast30yearswehaveseenliterallyhundredsofproprietaryandstandardprotocolsdeveloped,eachwiththeirownuniqueadvantages.TodaysPLChastobedatacompilersandinformationgateways.Theyhavetointerfacewithbarcodescannersandprinters,aswellastemperatureandanalogsensors.Theyneedmultipleprotocolsupporttobeabletoconnectwithotherdevicesintheprocess.Andfurthermore,theyneedallthesecapabilitieswhileremainingcost-effectiveandsimpletoprogram.AnotherprimarydevelopmentthathasliterallyrevolutionizedthewayPLCareprogrammed,communicatewitheachotherandinterfacewithPCsforHMI,第3页SCADAorDCSapplications,camefromthecomputingworld.UseofEthernetcommunicationsontheplantfloorhasdoubledinthepastfiveyears.Whileserialcommunicationsremainpopularandreliable,Ethernetisfastbecomingthecommunicationsmediaofchoicewithadvantagesthatsimplycantbeignored,suchas:*Networkspeed.*Easeofusewhenitcomestothesetupandwiring.*Availabilityofoff-the-shelfnetworkingcomponents.*Built-incommunicationssetups.IntegratedMotionControlAnotherresponsibilitythePLChasbeentaskedwithismotioncontrol.Fromsimpleopen-looptomulti-axisapplications,thetrendhasbeentointegratethisfeatureintoPLChardwareandsoftware.Therearemanyapplicationsthatrequireaccuratecontrolatafastpace,butnotexactprecisionatblazingspeeds.Theseareapplicationswherethestand-alonePLCworkswell.ManynanoandmicroPLCareavailablewithhigh-speedcountingcapabilitiesandhigh-frequencypulseoutputsbuiltintothecontroller,makingthemaviablesolutionforopen-loopcontrol.Theonecaveatisthatthecontrollerdoesnotknowthepositionoftheoutputdeviceduringthecontrolsequence.Ontheotherhand,itsmainadvantageiscost.Evensimplemotioncontrolhadpreviouslyrequiredanexpensiveoptionmodule,andattimeswasrestrictedtomoresophisticatedcontrolplatformsinordertomeetsystemrequirements.Moresophisticatedmotionapplicationsrequirehigher-precisionpositioninghardwareandsoftware,andmanyPLCofferhigh-speedoptionmodulesthatinterfacewithservodrives.Mostdrivestodaycanaccepttraditionalcommandsfromhost(PLCorPC)controls,orprovidetheirowninternalmotioncontrol.Thetrendhereistointegratethemotioncontrolconfigurationintothelogiccontrollerprogrammingsoftwarepackage.ProgrammingLanguagesAfacetofthePLCthatreflectsboththepastandthefutureisprogramminglanguage.TheIEC61131-3standarddealswithprogramminglanguagesanddefinestwographicalandtwotextualPLCprogramminglanguagestandards:*Ladderlogic(graphical).*Functionblockdiagram(graphical).*Structuredtext(textual).Instructionlist(textual).第4页Thisstandardalsodefinesgraphicalandtextualsequentialfunctionchartelementstoorganizeprogramsforsequentialandparallelcontrolprocessing.Basedonthestandard,manymanufacturersofferatleasttwooftheselanguagesasoptionsforprogrammingtheirPLC.Ironically,approximately96percentofPLCusersrecentlystilluseladderdiagramstoconstructtheirPLCcode.Itseemsthatladderlogiccontinuestobeatopchoicegivenitsperformedsowellforsolong.HardwarePlatformsThemodernPLChasincorporatedmanytypesofCommercialofftheShelf(COTS)technologyinitsCPU.ThislatesttechnologygivesthePLCafaster,morepowerfulprocessorwithmorememoryatlesscost.TheseadvanceshavealsoallowedthePLCtoexpanditsportfolioandtakeonnewtaskslikecommunications,datamanipulationandhigh-speedmotionwithoutgivinguptheruggedandreliableperformanceexpectedfromindustrialcontrolequipment.NewtechnologyhasalsocreatedacategoryofcontrollerscalledProgrammableAutomationControllers,orPAC.PACdifferfromtraditionalPLCinthattheytypicallyutilizeopen,modulararchitecturesforbothhardwareandsoftware,usingstandardsfornetworkinterfaces,languagesandprotocols.TheycouldbeviewedasaPCinanindustrialPLC-likepackage.TheFutureA2005PLCProductFocusStudyfromReedResearchGrouppointedoutfactorsincreasinglyimportanttousers,machinebuildersandthosemakingthepurchasingdecisions.Thetoppicksforfeaturesofimportancewere.Theabilitytonetwork,anddosoeasily.Ethernetcommunicationsisleadingthechargeinthisrealm.Notonlyarenewprotocolssurfacing,butmanyoftheindustrystandardserialprotocolsthathavebeenusedformanyyearsarebeingportedtoEthernetplatforms.EthernetcommunicationmodulesforPLCarereadilyavailablewithhigh-speedperformanceandflexibleprotocols.Also,manyPLCCPUarenowavailablewithEthernetportsonboard,savingI/Oslotspace.PLCwillcontinuetodevelopmoresophisticatedconnectivitytoreportinformationtootherPLC,systemcontrolsystems,dataacquisition(SCADA)systemsandenterpriseresourceplanning(ERP)systems.Additionally,wirelesscommunicationswillcontinuetogainpopularity.TheabilitytonetworkPLCI/OconnectionswithaPC.Thesametrendsthat第5页havebenefitedPLCnetworkinghavemigratedtotheI/Olevel.ManyPLCmanufacturersaresupportingthemostacceptedfieldbusnetworks,allowingPLCI/Otobedistributedoverlargephysicaldistances,orlocatedwhereitwaspreviouslyconsiderednearlyimpossible.ThishasopenedthedoorforpersonalcomputerstointerfacewithstandardPLCI/Osubsystemsbyusinginterfacecards,typicallysuppliedbythePLCmanufacturerorathirdpartydeveloper.NowthesechallenginglocationscanbemonitoredwithtodayaPC.Whereindustrial-gradecontrolenginesarenotrequired,theusercantakeadvantageofmoreadvancedsoftwarepackagesandhardwareflexibilityatalowercost.Theabilitytouseuniversalprogrammingsoftwareformultipletargets/platforms.Inthepastitwasexpectedthatanintelligentcontrollerwouldbecomplextoprogram.Thatisnolongerthecase.Usersarenolongerjusttrainedprogrammers,suchasdesignengineersorsystemsintegrator,butend-userswhoexpecteasier-to-usesoftwareinmorefamiliarformats.TheWindows-basedlookandfeelthatusersarefamiliarwithontheirpersonalcomputershavebecomethemostacceptedgraphicaluserinterface.WhatbeganassimplerelaylogicemulationforprogrammingPLChasevolvedintolanguagesthatusehigherlevelfunctionblocksthataremuchmoreintuitivetoconfigure.PLCmanufacturersarealsobeginningtointegratetheprogrammingofdiversefunctionsthatallowyoutolearnonlyonepackageinconfiguringlogic,HMI,motioncontrolandotherspecializedcapabilities.Possiblytheultimatewishoftheend-userwouldbeforasoftwarepackagethatcouldseamlesslyprogrammanymanufacturersPLCandsub-systems.Afterall,MicrosoftWindowsoperatingsystemandapplicationsworksimilarlywhetherinstalledonaDell,HPorIBMcomputer,whichmakesiteasierfortheuser.ApersonknowledgeableinrelaylogicsystemscanmasterthemajorPLCfunctionsinafewhours,Thesefunctionsmightincludecoils,contacts,timersandcounters.Thesameistrueforapersonwithadigitallogicbackground.Forpersonsunfamiliarwithladderdiagramsordigitalprinciples,butthelearningprocesstakesmoretime.ApersonknowledgeableinrelaylogiccanmasteradvancedPLCfunctionsinafewdayswithproperinstruction.Companyschoolsandoperatingmanualsareveryhelpfulinmasteringtheseadvancedfunctions.Advancedfunctionsinorderof第6页learningmightincludesequence/drumcontroller,registerbituse,andmorefunctions.Followingare8majoradvantagesofusingaprogrammablecontroller.Flexibility.Inthepast,eachdifferentelectronicallycontrolledproductionmachinerequiredowncontroller;15machinesmightrequire15differentcontrollers.NowitispossibletousejustonemodelofaPLCtorunanyoneofthe15machines.ImplementingChangeandCorrectingErrors.Withawiredrelay-typepanel,anyprogramalterationsrequiretimeforrewritingofpanelsanddevices.WhenaPLCprogramcircuitorsequencedesignchangeismade,thePLCprogramcanbechangedfromakeyboardsequenceinametterofminutes.NorewiringisrequiredforaPLC-controlledsystem.Largequantitiesofcontacts.ThePLChasalargenumberofcontactsforeachcoilavailableinitsprogramming.supposethatapanel-wiredrelayhasfourcontactsandallareinusewhenadesignchangerequiringthreemorecontactsismade.Timewouldhavetobetakentoprocureandinstallanewrelayorrelaycontactblock.UsingaPLC,butonlythreemorecontactswouldbetypedin.thethreecontactwouldbeautomaticallyavailableinthePLC.Indeed,ahundredcontactscanbeusedfromonerelay-ifsufficientcomputermemoryisavailable.Lowercost.Increasedtechnologymakesitpossibletocondensemorefunctionsintosmallerandlessexpensivepackages.NowyoucanpurchaseaPLCwithnumerousrelays,timersandcounters,asequencer,andotherfunctionforafewhundreddollars.PilotRunning.APLCprogrammedcircuitcanbeevaluatedintheofficeorlab.Theprogramcanbetypedin,tested,observed,andmodifiedifneeded,savingvaluablefactorytime.Incontrast,conventionalrelaysystemshavebeentestedonthefactoryfloor,whichcanbeverytimeconsuming.VisualObservation.APLCcircuitsoperationcanbeseenduringoperationdirectlyonaCRTscreen.Theoperationofacircuitcanbeobservedasithappens.Logicpathslightuponthescreenastheyareenergized.Troubleshootingcanbedonemorequicklyduringvisualobservation.InadvancedPLCsystems,anoperatormessagecanbeprogrammedforeachpossiblemalfunction.InadvancedPLCsystems,anoperatormessagecanbeprogrammedforeach第7页possiblemalfunction.ThemalfunctiondescriptionappearsonthescreenwhenthemalfunctionisdetectedbythePLClogic.AdvancedPLCsystemsalsomayhavedescriptionsofthefunctionofeachcircuitcomponent.SpeedofOperation.Relayscantakeanunacceptableamountoftimetoactuate.TheoperationalspeedforthePLCprogramisveryfast.ThespeedforthePLClogicoperationisdeterminedbyscantime,whichisamatterofmilliseconds.LadderorBooleanProgrammingMethod.ThePLCprogrammingcanbeaccomplishedintheladdermodebyanelectricianortechnician.Alternatively,aPLCprogrammerwhoworksindigitalorBooleancontrolsystemscanalsoeasilyperformPLCprogramming.Inmodernindustrialproductionequipment,andlargenumbersofsimulationsofthecontroldevices,suchastheceaseelectrical,electromagneticdevicestoturn,thenumberofproducts,temperature,APpower,andsettheflowcontrol,theautomaticcontroloftheindustrialsite,Ifaprogrammablecontroller(PLC)toresolvetheissuehasbecomeacyberneticoneofthemosteffectivetools,thisarticledescribesPLCcontrolsystemdesignshouldbenoted.HardwarepurchasemanyproductscurrentlyonthemarketPLC,withtheexceptionofdomesticbrands,foreign:Japan,Mitsubishi,FUJJ,ANASONIC,GermanySiemens,KoreanLG.Inrecentyears,PLCgreaterdeclineinthepricesofproducts,increasingitsperformancecostrate.ThisisatechnicalstaffchosenPLCimportantreasons.Then,howtopurchasePLCproducts?First,thesystemshouldfirstdeterminethesizeofsinglecontrolsystemwithPLCorusingPLCnetworking,thuscalculatingPLCimporting,exporting.Few,andinsomePLCtobeinrealneedhaveacertaincushionSecond,determinethetypeofloadunderPLCexport-ledtypeofloadistheDCorexchange-type,bigorsmallcurrents,andPLCexportpointssuchasthefrequencyofmovements,theuseofrelaystodetermineexport-export,ortransistoroutput,orgoodsofexportgates.Differentloadchoosedifferentwaystoexporttotheoperatingsystemsstabilityisveryimportant.Third,thestoragecapacityandspeedwhileforeignmanufacturersofPLCproductsessentiallythesame,buttherearesomedifferences.Currentlythecompanyhasnotyetfoundfullcompatibilitybetweenproducts.Thedevelopmentofsoftwarecompaniesarenotthesame,andusersofstoragecapacityand第8页procedurestoimplementtheDirectivespeedaretwoimportantindicators.Generalgreaterstoragecapacity,fasterspeedonthePLChigherprices,butshouldbebasedonsystemsizereasonablechoicePLCproducts.Fourth,programmingdevicesPLCprogrammingcanpurchasethreeways:Usinghand-heldprogrammingdeviceprogrammingingeneral,itcanprovidebusinessesphrasesprogramminglanguagetable.Thisapproachinefficient,butthecapacityofsmallsystems,theproductsmoresuitableforsmallconsumption,andsmallsize,easeofdebuggingscene,butalsolowercosts.Usinggraphicalprogrammingdeviceprogramming,theprogrammingdeviceusedTrapezoidChartprogrammingforvisualandgeneralelectricalpersonnelshortlybeappliedeasily,buttheprogrammingdevicepriceshigher.UsingIBMpersonalcomputersandsoftwarepackagesusingPLCprogramming,thisapproachisthemostefficientway,butmostofthecompanysPLCdevelopmentsoftwarepackagesexpensive,andthatmeansnotatthescenedebugging.Therefore,thesystemshouldbebasedonthesizeandlevelofdifficulty,thelengthofthedevelopmentcycleandreasonablefundingofthepurchasePLCproducts.Fifth,Andlargecompaniestochoosetheirqualityguaranteedproducts,andgoodtechnicalsupport,aftersalesservicesaregenerallybetter,butalsohelpexpandyourproductandsoftwareupgrades.Forsmallsystems,suchas80pointswithinthesystem.Generallydonotneedexpansion;Whenalargersystem,wemustexpand.Differentcompaniesproductstothetotalpointssystemandtheexpansionofthenumberofmoduleshavelimitationswhenexpansioncannotmeettherequirements,cannetworkstructure;Atthesametime,somemanufacturersofindividualproductsdonotsupporttheexpansionmoduledirectives,insoftwaredevelopment,wemustpayattentionto.Whenusingsuchsimulationmoduletemperature,someofthemanufacturers,seerelatedtechnicalmanuals.Manytypesofcompaniesexpansionmodules,suchassingle-inputmodules,singleoutputmodules,inputoutputmodules,temperaturemodules,high-speedinputmodule.ThismodulardesignPLCproductdevelopmentprovidedfortheconvenienceofusers.WhenusingaPLCnetworkdesign,itsmuchmoredifficulttocontrolthansinglePLC.Firstyoushouldchoosetheirownmorefamiliartype,itsbasicinstructionsandamorein-depthunderstandingofthefunctionalcommands,and第9页thespeedanddirectionoftheimplementationofstoragecapacityusersshouldalsobecarefulabouttheprocedure.Otherwise,youcannotadapttothereal-timerequirements,resultinginthecollapseofthesystem.Inadditiontocommunicationsinterfaces,communicationprotocols,datatransmissionspeedshouldalsobeconsidered.Finally,wemustseektoPLCbusinessmennetworkdesignandsoftwaretechnicalsupportanddetailedtechnicalinformationfortheselectionofseveralworkstationsinyoursystemsize.Inthepreparationofthesoftware,shouldfirstbecomefamiliarwiththeuseofPLCsoftwareproductsspecification,thequestionskilledlaterprogramming.Ifusinggraphicalprogrammingdeviceorsoftwarepackageprogrammingmaydirectprogramming,ifusinghand-heldprogrammingdeviceprogramming,shouldbepaintedTrapezoidChartbeforeprogramming,socanlessmistakesspeedwasfast.Afterthefirstairconditioningprogrammingprocedurestobenormalfunctioningofall,againinequipmentdebugging.第10页中文翻译稿PLC控制系统设计的要点可编程序控制器(可设计的控制器)本来应简称个人计算机，为了与个人计算机的简称个人计算机相区别,一般将它简称为PLC(可设计的逻辑控制器)。PLC是一个方便使用，是实行许多类型和复杂层的控制功能的基于微处理器的特殊计算机.它的目的是适当地检测决定性的程序叁数并且调整程序操作。在操作计算机方面不熟练的人能对它进行规划，控制,而且操作。本质上,一个PLC的操作员在一个展览荧屏之上用一个键盘画梯图表的线和装置.产生的图画转换成计算机机器语言和作为一个用户程序运行。计算机代替了一个过程控制所需的许多外部配线。PLC将会操作有开或关的输出装置的任何系统(已知不连续的，或数字的,输出)。它也能操作任何输出为变量(模拟)的系统.PLC能通过开关装置(不连续的,或数字的)或输入变量(模拟)的装置在输入端进行操作。今天,在PLC工业中的大单位增长就要结束-因为小的变得越来越小。微PLC数年以前进入了市场，一些人认为这些装置降到最低点。现在,十亿分之一PLC-通常定义了16或者较少的输入输出-正在广泛应用。一些能装在你的衬衫口袋，没有一副卡片大并且能在任何时间写作,引入的PLC将会包括现在微模型的许多特征,它只有Tic-Tac的糖果盒子的大小。从本质上讲，PLC是一种用高度专业化语言编程的工业计算机，并继续受益于计算机和信息技术领域的技术进步。它的最突出之处是小型化和通信功能。微型化的PLC在最初引进PLC的时候，主要改进它的体积，这与替换了数百个硬接线继电器和计时器有关。一个嵌有CPU和I/O的典型单元有大约19寸电视机那么大。从20世纪80年代到20世纪90年代初，模块化的PLC逐渐微型化，同时它的容量和性能也得到了提高。近年来，更小型PLC已经发展到纳米级和微型级，它们已具有以前只在大型PLC上才有的特点。因此仅为了额外特性或性能而不是增加I/O容量而具体指定一个大型的PLC变得不必要，因为即使纳米级PLC也具备以太网通信、运动控制、自动调谐的嵌入式PID、远程连通性等更多的功能。第11页现在，由于PLC能执行运动控制、数据采集，远程终端单元（RTU）甚至一些集成人机介面（HMI）等功能，因此PLC在很多应用中也已配置齐全从而替代单一的过程控制器。以前，这些功能通常要求他们自身内置实现这些功能的控制器和软件，此外，还需要一个用于离散控制和互锁的独立的PLC。强大的通信功能近年来，最有意义的变化也许发生在通信领域。在20世纪90年代，Modicon推行的Modbus通信协议，允许PLC通过标准电缆进行通信。这为PLC更好地适用于现存的设备提供了可能性，并且向主板上的其它控制系统通信成为可能。在过去的30年里，我们真实地目睹了数百个专利化协议和标准化协议的发展，每一个协议都有自己独特的优势。现在，PLC已成为数据编译器和信息网关，它们必须接入条形码扫描器和打印机，还有温度和模拟传感器。在过程控制中，它们需要支持多种协议，以便它们能和其它设备通信。此外，在它们全部具备这些功能的同时，它们仍然要有高的性价比而且编程简单。另一个主要改进来自于计算处理领域。确切地说，它革命化了PLC的编程方式、互相通信、与用于HMI、SCADA和DCS的PC有接口。在过去的五年中，车间级以太网通信的应用已经翻了一倍。尽管串行通信仍然很受欢迎并且很可靠，但以太网快速地成为值得选择的通信媒体，它有着不能被忽视的优势，例如：网速、设置简单、布线方便、现成网络组件的可用性