plc外文文献译文

00ProgrammablelogiccontrollerAprogrammablelogiccontroller(PLC）isadigitalcomputerusedforautomationofelectromechanicalprocesses，suchascontrolofmachineryonfactoryassemblylines,amusementrides，orlightingfixtures.PLCisusedinmanyindustriesandmachines.1。HistoryThePLCwasinventedinresponsetotheneedsoftheAmericanautomotivemanufacturingindustry.Beforethecontrol，sequencing,andsafetyinterlocklogicformanufacturingautomobileswasaccomplishedusinghundredsorthousandsofrelays,camtimersanddrumsequencersanddedicatedclosed-loopcontrollers。In1968GMHydramaticissuedarequestforproposalforanelectronicreplacementforhard—wiredrelaysystems。ThefirstPLC,designatedthe084becauseitwasBedfordAssociates’project,wastheresultBedfordAssociatesstartedanewcompanydedicatedtodeveloping,manufacturingsellingandservicingthisnewproduct：Modicon，whichstoodforMOdularDIgitalCONtroller。TheModiconbrandwassoldin1977toGouldElectronics,andlateracquiredbyGermanCompanyAEGandthenbyFrenchSchneiderthecurrentowner.Oneofveryfirst084modelsthatwaspresentedtoModiconbyGM,whentheunitwasretiredafternearlytwentyyearsofuninterruptedservice.Modiconusedthe84monikerattheendofitsproductrangeuntilthe984madeitsappearance。2.DevelopmentEarlyPLCsweredesignedtoreplacerelaylogicsystems.ThesePLCswereprogrammedin"ladderlogic”,whichstronglyresemblesaschematicdiagramofrelaylogic。OtherearlyPLCsusedaformofinstructionlistprogramming，basedonastack-basedlogicsolver.ModernPLCscanbeprogrammedinavarietyofways,fromladderlogictomoretraditionalprogramminglanguagessuchasBASICandC。AnothermethodisStateLogic，averyhigh—levelprogramminglanguagedesignedtoprogramPLCsbasedonstatetransitiondiagrams。3.FunctionalityThefunctionalityofthePLChavesequentialrelaycontrol,motioncontrol,process control，distributed control systems and networking.Regarding practicalityofthesedesktopcomputerbasedlogiccontrollers,itisimportanttonotethattheyhavenotbeengenerallyacceptedinheavyindustrybecausethedesktopPAGEPAGE6computersrunonlessstableoperatingsystemsthandoPLCs，andbecausethedesktopcomputerhardwareistypicallynotdesignedtothesamelevelsoftolerancetotemperature,Inmorerecentyears,smallproductscalledPLRs（programmablelogicrelays),areusedinlightindustrywhereonlyafewpointsofI/Oieafewsignalscominginfromtherealworldandafewgoingout）areinvolved,andlowcostisdesiredPopularnamesincludePICOController，NANOPLC，andothernamesimplyingverysmallcontrollers.thePLRsareusuallynotmodularorexpandable，buttheirpricecanbetwoordersofmagnitudelessthanaPLCandtheystillofferrobustanddeterministicexecutionofthelogic。PLCcomparedwithothercontrolsystemsPLCsarewell—adaptedtoarangeofautomationtasks。Thesearetypicallyindustrialprocessesinmanufacturingwherethecostofdevelopingandmaintainingtheautomationsystemishighrelativetothetotalcostoftheautomation，andchangestothesystemwouldbeexpectedduringitsoperationallife.PLCscontaininputandoutputdevicescompatiblewithindustrialpilotdevicesandcontrols;littleelectricaldesignisrequired，andthedesignproblemcentersonexpressingthedesiredsequenceofoperations。PLCapplicationsaretypicallyhighlycustomizedsystemssothecostofapackagedPLCislowcomparedtothecostofaspecificcustom-builtcontrollerdesign.Ontheotherhand ，inthecaseofmass—producedgoods,customizedcontrolsystemsareeconomicduetothelowercostofthecomponents，whichcanbeoptimallychoseninsteadofa”generic”solution,andwherethenon—recurringengineeringchargesarespreadoverthousandsormillionsofunits.Amicrocontroller-baseddesignwouldbeappropriatewherehundredsorthousandsofunitswillbeproducedandsothedevelopmentcost(designofpowersupplies，input/outputhardwareandnecessarytestingandcertification)canbespreadovermanysales,andwheretheend-userwouldnotneedtoalterthecontrol.Automotiveapplicationsareanexample;millionsofunitsarebuilteachyear,andveryfewend-usersaltertheprogrammingofthesecontrollers。However，specialtyvehiclessuchastransitbusseseconomicallyusePLCsinsteadcustom-designedcontrols,becausethevolumesarelowandthedevelopmentcostwouldbeuneconomic.Programmablecontrollersarewidelyusedinmotioncontrol，positioningcontrolandtorquecontrol.SomemanufacturersproducemotioncontrolunitstobeintegratedwithPLCsothatG—code(involvingaCNCmachine)canbeusedtoinstructmachinemovements.PLCsmayincludelogicforsingle-variablefeedbackanalogcontrolloop,a”proportional，integral，derivative”or"PIDcontroller"APIDloopcouldbeusedtocontrolthetemperatureofamanufacturingprocess,forexample.HistoricallyPLCswereusuallyconfiguredwithonlyafewanalogcontrolloops;whereprocessesrequiredhundredsorthousandsofloopsadistributedcontrolsystem(DCS）insteadbeused。AsPLCshavebecomemorepowerfultheboundarybetweenDCSandPLCapplicationshasbecomelessdistinct.PLCshavesimilarfunctionalityasRemoteTerminalUnits.AnRTU,however，usuallydoesnotsupportcontrolalgorithmsorcontrolloops.Ashardwarerapidlybecomesmorepowerfulandcheaper,RTUs，PLCsandDCSsareincreasinglybeginningtooverlapinresponsibilities,andmanyvendorssellRTUswithPLC-likefeaturesandviceversa。TheindustryhasstandardizedontheIEC61131-3functionalblocklanguageforcreatingprogramstorunonRTUsandPLCs,althoughnearlyallvendorsalsoofferproprietaryalternativesandassociateddevelopmentenvironments.Theprospectsfor。5。1FeaturesThemaindifferencefromothercomputersisthatPLCsarearmoredforsevereconditions(suchasdust，moisture,heat,cold）andhavethefacilityforextensiveinput/output（I/O）arrangements.PLCsreadlimitswitches，analogprocessvariables（suchastemperatureandpressure）,andthepositionsofcomplexpositioningsystems.Someusemachinevision。Ontheactuatorside,PLCsoperateelectricmotors，pneumaticorhydrauliccylinders,magneticrelays，solenoids，analogoutputs。Theinput/outputarrangementsmaybebuiltintoasimplePLC,orthePLCmayhaveexternal I/OmodulesattachedtoacomputernetworkthatplugsintothePLC。5.2SystemscaleAsmallPLCwillhaveafixednumberofconnectionsbuiltinforinputsoutputs。Typically,expansionsareavailableifthebasemodelhasinsufficientI/O.ModularPLCshaveachassis （alsocalledarack）intowhichareplacedmoduleswithdifferentfunctions。TheprocessorandselectionofI/Omodulesiscustomisedfortheparticularapplication.Severalrackscanbeadministeredbyasingleprocessor,andmayhavethousandsofinputsandoutputsAspecialhighspeedserialI/Olinkusedsothatrackscanbedistributedawayfromtheprocessor，reducingthewiringcostsforlargeplants。5。3UserinterfacePLCsmayneedtointeractwithpeopleforthepurposeofconfiguration,alarmreportingoreverydaycontrol。Asimplesystemmayusebuttonsandlightstointeractwiththeuser.Textdisplaysareavailableaswellasgraphicaltouchscreens.Morecomplex systems use a programming and monitoring software installed on acomputer，withthePLCconnectedviaacommunicationinterface.5.4CommunicationsPLCshavebuiltincommunicationsports，usually9—pinRS-232，butoptionallyEIA-485orEthernet.Modbus，BACnetorDF1isusuallyincludedasofthecommunicationsprotocols.OtheroptionsincludevariousfieldbusessuchasDeviceNetorProfibus.OthercommunicationsprotocolsthatmaybeusedarelistedintheListofautomationprotocols。MostmodernPLCscancommunicateoveranetworktosomeothersystem，suchasacomputerrunningaSCADA（SupervisoryControlAndDataAcquisition）systemorwebbrowser.PLCsusedinlargerI/Osystemsmayhavepeer—to-peer（P2P)betweenprocessors.This allowsseparateparts ofacomplexprocesstoindividual control while allowing the subsystems to co-ordinate over communicationlink.ThesecommunicationlinksarealsooftenusedforHMIdevicessuchaskeypadsorPC-typeworkstations。可编程逻辑控制器可编程逻辑控制器1。历史PLCPLC之前,Hydramatic发布通用汽车公.PLC选定和服务这一新产品:Modicon,1977年古尔德电子公司当AEGModicon。这是专门为通用汽车服务的，并且经过了近二十多年的不间断服务。直至984出现，Modicon使用的84名字才在其产品范围中结束。2。发展早期的可编程控制器是设计来取代继电器逻辑系统。这些可编程控制器的“阶梯逻辑”是与继电器逻辑示意图非常类似的.其他早期的可编程控制器使用指令列表编程，基于一个堆