PLC相关的外文英语文献与翻译

1、RelaysTheProgrammableLogicControllerEarlymachineswerecontrolledbymechanicalmeansusingcams,gears,leversandotherbasicmechanicaldevices.Asthecomplexitygrew,sodidtheneedforamoresophisticatedcontrolsystem.Thissystemcontainedwiredrelayandswitchcontrolelements.Theseelementswerewiredasrequiredtoprovidethecontrollogicnecessaryfortheparticulartypeofmachineoperation.Thiswasacceptableforamachinethatneverneededtobechangedormodified,butasmanufacturingtechniquesimprovedandplantchangeovertonewproductsbecamemor。

2、edesirableandnecessary,amoreversatilemeansofcontrollingthisequipmenthadtobedeveloped.Hardwiredrelayandswitchlogicwascumbersomeandtimeconsumingtomodify.Wiringhadtoberemovedandreplacedtoprovideforthenewcontrolschemerequired.Thismodificationwasdifficultandtimeconsumingtodesignandinstallandanysmallbuginthedesigncouldbeamajorproblemtocorrectsincethatalsorequiredrewiringofthesystem.Anewmeanstomodifycontrolcircuitrywasneeded.ThedevelopmentandtestinggroundforthisnewmeanswastheU.S.autoindustry.Thetimeper。

3、iodwasthelate1960'sandearly1970'sandtheresultwastheprogrammablelogiccontroller,orPLC.Automotiveplantswereconfrontedwithachangeinmanufacturingtechniqueseverytimeamodelchangedand,insomecases,forchangesonthesamemodelifimprovementshadtobemadeduringthemodelyear.ThePLCprovidedaneasywaytoreprogramthewiringratherthanactuallyrewiringthecontrolsystem.ThePLCthatwasdevelopedduringthistimewasnotveryeasytoprogram.Thelanguagewascumbersometowriteandrequiredhighlytrainedprogrammers.Theseearlydevicesweremerelyrel。

4、ayreplacementsandcoulddoverylittleelse.ThePLChasatfirstgradually,andinrecentyearsrapidlydevelopedintoasophisticatedandhighlyversatilecontrolsystemcomponent.Unitstodayarecapableofperformingcomplexmathfunctionsincludingnumericalintegrationanddifferentiationandoperateatthefastmicroprocessorspeedsnowavailable.OlderPLCswerecapableofonlyhandlingdiscreteinputsandoutputs(thatis,on-offtypesignals),whiletoday'ssystemscanacceptandgenerateanalogvoltagesandcurrentsaswellasawiderangeofvoltagelevelsandpulsedsi。

5、gnals.PLCsarealsodesignedtoberugged.Unliketheirpersonalcomputercousin,theycantypicallywithstandvibration,shock,elevatedtemperatures,andelectricalnoisetowhichmanufacturingequipmentisexposed.AsmoremanufacturersbecomeinvolvedinPLCproductionanddevelopment,andPLCcapabilitiesexpand,theprogramminglanguageisalsoexpanding.Thisisnecessarytoallowtheprogrammingoftheseadvancedcapabilities.Also,manufacturerstendtodeveloptheirownversionsofladderlogiclanguage(thelanguageusedtoprogramPLCs).Thiscomplicateslearnin。

6、gtoprogramPLC'singeneralsinceonelanguagecannotbelearnedthatisapplicabletoalltypes.However,aswithothercomputerlanguages,oncethebasicsofPLCoperationandprogramminginladderlogicarelearned,adaptingtothevariousmanufacturers’devicesisnotacomplicatedprocess.MostsystemdesignerseventuallysettleononeparticularmanufacturerthatproducesaPLCthatispersonallycomfortabletoprogramandhasthecapabilitiessuitedtohisorherareaofapplications.Itshouldbenotedthatinusage,aprogrammablelogiccontrollerisgenerallyreferredtoasa“。

7、PLC”or“programmablecontroller”.Althoughtheterm“programmablecontroller”isgenerallyaccepted,itisnotabbreviated“PC”becausetheabbreviation“PC”isusuallyusedinreferencetoapersonalcomputer.Aswewillseeinthischapter,aPLCisbynomeansapersonalcomputer.Programmablecontrollers(theshortenednameusedforprogrammablelogiccontrollers)aremuchlikepersonalcomputersinthattheusercanbeoverwhelmedbythevastarrayofoptionsandconfigurationsavailable.Also,likepersonalcomputers,thebestteacherofwhichonetoselectisexperience.Asone。

8、gainsexperiencewiththevariousoptionsandconfigurationsavailable,itbecomeslessconfusingtobeabletoselecttheunitthatwillbestperforminaparticularapplication.ThetypicalsystemcomponentsforamodularizedPLCare:1.Processor.Theprocessor(sometimescallaCPU),asintheselfcontainedunits,isgenerallyspecifiedaccordingtomemoryrequiredfortheprogramtobeimplemented.Inthemodularizedversions,capabilitycanalsobeafactor.Thisincludesfeaturessuchashighermathfunctions,PIDcontrolloopsandoptionalprogrammingcommands.Theprocessor。

9、consistsofthemicroprocessor,systemmemory,serialcommunicationportsforprinter,PLCLANlinkandexternalprogrammingdeviceand,insomecases,thesystempowersupplytopowertheprocessorandI/Omodules.2.Mountingrack.ThisisusuallyametalframeworkwithaprintedcircuitboardbackplanewhichprovidesmeansformountingthePLCinput/output(I/O)modulesandprocessor.Mountingracksarespecifiedaccordingtothenumberofmodulesrequiredtoimplementthesystem.Themountingrackprovidesdataandpowerconnectionstotheprocessorandmodulesviathebackplane.。

10、ForCPUsthatdonotcontainapowersupply,therackalsoholdsthemodularpowersupply.Therearesystemsinwhichtheprocessorismountedseparatelyandconnectedbycabletotherack.Themountingrackcanbeavailabletomountdirectlytoapanelorcanbeinstalledinastandard19wideequipmentcabinet.MountingracksarecascadablesoseveralmaybeinterconnectedtoallowasystemtoaccommodatealargenumberofI/Omodules.3.Inputandoutputmodules.Inputandoutput(I/O)modulesarespecifiedaccordingtotheinputandoutputsignalsassociatedwiththeparticularapplication.T。