Foundation of PLC外文翻译PLC发展史Word文件下载.docx

Foundation of PLC外文翻译PLC发展史Word文件下载.docx

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外文翻译

专业：

班级学号：

学生姓名：

指导教师：

二〇一一年六月

本科生毕业设计

原文1：

Programmablelogiccontrollers

译文1：

可编程逻辑控制器

原文2：

FoundationofPLC

译文2：

PLC基础

专业班级：

学院：

2011年6月

Programmablelogiccontroller（PLC）iseight10-Yearonbehalfnewgenerationindustrythatdevelopthecontrolequip,andisanautomaticcontrol,calculatorwiththethingthatthecorrespondencetechniquecombinetogether,andisathespotequipmentsforexclusivelyusedforingtheindustryproductionlinecontroling.MakethePLCthereischaracteristicsofobviousoneselfonthedesignwiththelong-termandcontinuousthatcirculatebecauseofthespecialofthecomplexity,usageenvironmentofthecontrolobject:

Thedependableishigh,andtheadaptabilityiswide,andhavetocorrespondbyletterthefunction,andweavethetheconvenience,constructionmoldpiece.Gatherthethecontrolinthemoderninthesystem,thePLChavealreadybecomeakindofimportanceofbasiccontrolunit,controltherealmtheinsideintheindustryappliedtheforegroundisveryandextensive.

Aprogrammablelogiccontroller（PLC）isasolid-statedevideusedtocontrolmachinemotionorprocessoperationbymeansofastoredprogram.ThePLCsendsoutputcontrolsignalsandreceivesinputsignalsthroughinput/output（I/O）devices.APLCcontrolsoutputsinresponsetostimuliattheinputsaccordingtothelogicprescribedbythestoredprogram.Theinputsaremadeupoflimitswitches,pushbuttons,thumbwheels,switches,pulses,analogsignals,ASCIIserialdata,andbinaryorBCDdatafromabsolutepositionencoders.Theoutputsarevoltageorcurrentleverstodriveenddevicessuchaslolenids,motorstaters,relays,lights,andsoon.Otheroutputdevicessuchincludeanalogdevices,digitalBCDdisplays,ASCIIcompatibledevices,servovariable-speeddrives,andevencomputers.

Programmablecontrollersweredeveloped（circain1968）whenGeneralMotorsCorp,andotherautomobilemanufacturerswereexperimentingtoseeiftheremightbeanalterantivetoscrappingalltheirhardwiredcontrolpanelsofmachinetoolsandotherproductionequipmentduringamodelchangeover.Thisannualtraditionwasnecessarybecauserewiringofthepanelswasmoreexpensivethanbuyingnewoens.

Theautomotivecompaniesapproachedanumberofcontrolequipmentmanufacturersandaskedthemtodevelopacontrolsystemthatwouldhavealongerproductivelifewithoutmajorrewiring,butwouldstillbeunderstandabletoandrepairablebyplantpersonnel.Thenewproductwanamda“programmablecontroller”．

TheprocessorpartofthePLCcontainsacentralprocessingunitandmemory.Thecentralprocessingunit（CPU）isthe“trafficdirector”oftheprocessor,thememorystoresinformation.Comingintotheprocessoraretheelectricalsignalsfromtheinputdevices，asconditionedbytheinputmoduletovoltagelevelsacceptabletoprocessorlogic．TheprocessorscansthestateofI／OandupdatesoutputsbasedoninstructionsstoredinthememoryofthePLC．Forexample，theprocessormaybeprogrammedsothatifaninputconnectedtoalimitswitchistrue（1imitswitchclosed）,thenacorrespondingoutputwiredtoanoutputmoduleistobeenergized．Thisoutputmightbeasolenoidforexample．Theprocessorremembersthiscommandthroughitsmemoryandcomparesoneachscantoseeifthatlimitis,infact,closed.Ifitisclosed,theprocessorenergizesthesolenoidbyturningontheoutputmodule.

Theoutputdevice,suchasasolenoidormotorstater,iswiredtoanoutputmofule’sterminal,anditreceivesitsshiftsignalfromtheprocessor,ineffectthepeocessorisperformingalongandcomplicatedseriesoflogicdecisions.ThePLCperformssuchdecisionssequentiallyandinaccordancewiththestoredprogram.similarly,analogI/Oallowstheprocessortomakedecisionsbasedonthemagnitudeofasignal,ratherthanjustifisonoroff.Forexample,theprocessormaybeprogrammestoencreaseordecreasethesteamflowtoaboiler（analogoutput）basedonacomparisonoftheactualtemperatureintheboiler（analoginput）tothedesiredtemperature.thisisoftenperformedbyutilizingthebuilt-inPID（proportional,integral,derivative）capabilitiesoftheprocessor.

Properpowertotheprogrammablecontrolleriscritical.Today’ssystemsareavailableinawidevarietyofelectricalconfigurations.Virtuallyallaredesignedforuseinsingle-phasepowersystems,andmostarenowbeginningtobeofferedwiththeoptionalabilitytooperateinaDCsupplyenvironment.ACdesignsareofferedineithersinglevoltagesupplies,suchas115or230VAC;

whilesomecanbeconfiguredaseitherthroughaselectionmadeonthepowersupply.Propergroundingofthepowersupplyconnectionisrequiredforasafeinstallation.Someprogrammablecontrollerdesignshaveindividualgroundingconnectionsfromracktoface-platesandothersystemcomponents,socaremustbetakentofollowwellelectricalpracticeinsystemgroundingduringelectricalinstallation.Incertainapplications,a24or120VDCpowersupplyisrequired.ThisiscommonforinstallationsthataxemadewherenoACpowerisavailable,suchasremoteelectricalgenerationstations.ItisalsofoundwhereACpowerisunreliableandwherelossofcontrolisconsideredanunacceptablesituation

Eventhebestoftoday'

swell-designedandmanufacturedprogrammablecontrollersrequireoccasionalpreventativemaintenanceandrepair.Thissectionlooksatsomeofthetoolsprovidedbythemanufacturerandtechniquesforgeneralmaintenance.Mostofthemedium-andlarge-sizedprogrammablecontrollersystemsavailabletodayaredesignedtobemaintainedbyindividualswithawidevarietyofskills,withoutthebenefitofin-depthformaltrainingofthispieceofequipment.Thisisaccomplishedinthedesignbyprovidingindividualmodulesoffunctionalityinstalledinachassisservicedfromthefront（allmoduletypesincludingpowersupplies）.Frontaccessiscriticaltopropermaintenance.Thisallowseasyinspectionandreplacementofthesuspectedbadmodule.ModulehealthisdeterminedbyinspectingtheLEDindicatorsnormallyprovidedonthefrontofeachmodule.Typicalindicatorswillbeonoroffdependingonthedesignandindividualconditionofthemoduleinquestion.VariousCPUandI/OmoduleswillhaveindicatorsshowingI/Ocontrolcommunicationsstatus,memoryintegrity,powersupplytolerancecheck,scanintegrity,andothers.Onfuturecontrollerdesigns,andeventodayonafewsystems,itislikelythatEnglishlanguagemessageswillbedisplayedonthecontrolleradvisingtheuserormaintenancepersonnelthataparticularfailurehasoccurredandrecommendedactionstotake.

Themodulardesignanddiagnosticindicatorsare,ofcourse,important,butwouldbequiteuselesswithoutwelldesigneddocumentationprovidedbythemanufacturerfortheprogrammablecontrollersysteminquestion.ProperdocumentationwillhavesectionsdedicatedtoeachmajorsubsystemincludingCPU,I/O,andprogrammingdevice.Eachshouldexplainindepththestop-by-stopinspectionofthesystem.Allpossiblecombinationsoffailuremodeshouldbelisted,alongwithsuggestedactionsforrepair.Thiswillmostofteninvolveonlythesubstitutionofare-placementboardforthesuspectedfailedunit.Theuserisurgedtopurchaseasetofsparemodulesforthesysteminquestionasrecommendedbythemanufacturer.Thisisnormally,ataminimum,asinglereplacementmoduleforeachCPUandprogrammingdeviceserviceablemodule,andspareI/Omodulesequalto10%ofthenumberinthesystem.

BecauseaPLCis“softwarebased”,itscontrollogicfunctionscanbechangedbyreprogrammingitsmemory.Keyboardprogrammingdevicesfacilitateentryoftherevisedprogram,whichcanbedesignedtocauseanexistingmachineorprocesstooperateinadifferentsequenceortorespondtodifferentlevelsof,orcombinationsofstimuli.Hardwaremodificationsareneededonlyifadditional,changed,orrelocatedinput/outputdevicesareinvolved.

Programmablecontrollermemoryisformattedintobits,bytes,andwordsofmemory.Abitisasinglestorageelementforeitherazerooraone.Abyteconsistsofeightbits,andaword（normally）consistsof16bits,ortwobytes.Somesystemsstilluseawordlengthofeightbits,butmosthaveadopteda16bitword,eventhoughtheymayusean8bitmicroprocessor.

Dependingonthespecificdesignoftheprogrammablecontroller,itwillhaveastatedmemorycapacity.Thisisanindication,althoughnottheonlyone,ofthecapabilityandpowerofthesystem.Mediumandlargecontrollersarenormallyexpandablefromonememorysizetotheirmaximumsize.Smallcontrollersarenormallyfixedintheirmemorysize.Sizeofthememorycapacitymustbeexaminedrelativetothewordsize（8bitor16bit）andutilization.Whileitisclearthattwicetheinformationcanbestoredina16bitwordthaninan8bitword,itmaynotbeimmediatelyclearthatsomecontrollersutilizememorymoreefficientlythanothers.Forexample,anormallyopencontactanditsassociatedreferenceaddress（e.g.Input1）,mayusein8bitbyteeachforstorage.Combined,theyconsumeone16bitword.Somecontrollersmayusemorememorythanthisfortheseinstructionsorothers.Inalargeprogram,theseinefficienciescanbuildoneachothertocauseapoorutilizationofthesystemmemory.Acarefulanalysisofthevariousprogrammablecontrollermodelsisrequiredtoassessutilizationefficiency.Normalpracticecallsforanadditional20%-40%ofmemorysizetobespecifiedtoallowformodificationsandlaterexpansion.Thisanalysis,combinedwithknowledgeoftheapplicationneeds,willallowforanintelligen