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文献翻译

南昌工程学院

07级毕业（设计）论文文献翻译

机械与电气工程系（院）电气工程及其自动化专业

题目基于PLC污水处理控制系统

学生姓名杨佳明

班级电气工程及其自动化

（1）班

学号2007100038

指导教师代芳

日期2011年01月06日

南昌工程学院教务处订制

评语：

指导教师：

年月日

PLC

Abstract:

Asakindofindustrialequipmentpowerhouses,withitsstraightawayprogramminganditsstablejobperformanceinbadenvironment,PLCwonthegeneralcustomers.PLChasbeenwidelyusedinindustrialareas,includingmachinerymanufacturing,transportationsystem,andchemicalprocessequipment,suchasmanyotherfields.Althoughcomputercontroltechnologyhascreated,itshighperformanceandlowcost,andthebadenvironmenthavestrongadaptability,soPLCcontroliswidelyusedinindustrialcontrol.

Keywords:

ProgrammableLogicController（PLC）；software

1.ThedevelopmentofPLC

Programmablecontrollerappearedinthelate1960sintheUnitedStates,andthePLC（ProgrammableLogicController）isusedtoreplacerelays.Fortheimplementationofthelogicaljudgment,timing,sequencenumber,andothercontrolfunctions.TheconceptofPLCispresentedbyGeneralMotorsCorporation.ThebasicdesignofPLCisthoseoverallscombinedthecomputerfunctionalimprovements,suchasflexible,generic,relaycontrolsystemsimpleandeasytooperate,andwiththeadvantagesofcheappricescombinedcontrollerhardware.Accordingtothepracticalapplicationoftargetsoftware,thecontentwritestotheuserproceduresmemorycontroller.Thecontrollercanbeconnectedeasilywiththeaccusedconvenienttarget.

Inthemid-1970s,thePLChasbeenwidelyusedasacentralprocessingunitmicroprocessor,importexportmoduleandtheexternalcircuitsareused,large-scaleintegratedcircuitsevenwhenthePLCisnolongertheonlylogical（IC）judgmentfunctionsalsohavedataprocessing,PIDconditioninganddatacommunicationsfunctions.InternationalElectrotechnicalCommission（IEC）standardspromulgatedprogrammablecontrollerforprogrammablecontrollerdraftmadethefollowingdefinition:

programmablecontrollerisadigitalelectroniccomputersoperatingsystem,specificallyforapplicationsintheindustrialdesignenvironment.Itusedprogrammablememory,usedtoimplementlogicintheirinternalstorageoperations,sequencecontrol,timing,countingandarithmeticoperations,suchasoperatinginstructions,andthroughdigitalandanaloginputandoutput,thecontrolofvarioustypesofmachineryorproductionprocesses.Programmablecontrollerandrelatedperipherals,andindustrialcontrolsystemseasilylinkedtoformawhole,toexpanditsfunctionaldesign.Programmablecontrollerfortheuser,isnoncontactequipment,theprocedurescanbechangedtochangeproductionprocesses.Theprogrammablecontrollerhasbecomeapowerfultoolforfactoryautomation,widelypopularreplication.Programmablecontrollerisuser-orientedindustriesdedicatedcontrolcomputer,withmanydistinctivefeatures.

①Highreliability,anti-interferencecapability;

②Programmingvisual,simple;

③Adaptabilitygood;

④Functionalimprovements,strongfunctionalinterface.

2.ThestructureofthePLC

CentralProcessingUnit（CPU）isthebrainofaPLCcontroller.CPUitselfisusuallyoneofthemicrocontrollers.Aforetimethesewere8-bitmicrocontrollerssuchas8051,andnowtheseare16-and32-bitmicrocontrollers.Unspokenruleisthatyou’llfindmostlyHitachiandFujicumicrocontrollersinPLCcontrollersbyJapanesemakers,SiemensinEuropeancontrollers,andMotorolamicrocontrollersinAmericanones.CPUalsotakescareofcommunication,interconnectednessamongotherpartsofPLCcontrollers,programexecution,memoryoperation,overseeinginputandsettingupofanoutput.PLCcontrollershavecomplexroutinesformemorycheckupinordertoensurethatPLCmemorywasnotdamaged（memorycheckupisdoneforsafetyreasons）.Generallyspeaking,CPUunitmakesagreatnumberofcheck-upsofthePLCcontrolleritselfsoeventualerrorswouldbediscoveredearly.YoucansimplylookatanyPLCcontrollerandseethatthereareseveralindicatorsintheform.Lightdiodesforerrorsignalization.

Systemmemory（todaymostlyimplementedinFLASHtechnology）isusedbyaPLCforaprocesscontrolsystem.Asideform.Thisoperatingsystemitalsocontainsauserprogramtranslatedformaladderdiagramtoabinaryform.FLASHmemorycontentscanbechangedonlyincasewhereuserprogramisbeingchanged.PLCcontrollerswereusedearlierinsteadofPLASHmemoryandhavehadEPROMmemoryinsteadofFLASHmemorywhichhadtobeerasedwithUVlampandprogrammedonprogrammers.WiththeuseofFLASHtechnologythisprocesswasgreatlyshortened.Reprogrammingaprogrammemoryisdonethroughaserialcableinaprogramforapplicationdevelopment.

Usermemoryisdividedintoblockshavingspecialfunctions.Somepartsofamemoryareusedforstoringinputandoutputstatus.Therealstatusofaninputisstoredeitheras“1”oras“0”inaspecificmemorybit/eachinputoroutputhasonecorrespondingbitinmemory.Otherpartsofmemoryareusedtostorevariablecontentsforvariablesusedinusedprogram.Forexample,timevalue,orcountervaluewouldbestoredinthispartofthememory.

PLCcontrollercanbereprogrammedthroughacomputer（usualway）,butalsothroughmanualprogrammers（consoles）.ThispracticallymeansthateachPLCcontrollercanprogrammedthroughacomputerifyouhavethesoftwareneededforprogramming.Today’stransmissioncomputersareidealforreprogrammingaPLCcontrollerinfactoryitself.Thisisofgreatimportancetoindustry.Oncethesystemiscorrected,itisalsoimportanttoreadtherightprogramintoaPLCagain.ItisalsogoodtocheckfromtimetotimewhetherprograminaPLChasnotchanged.Thishelpstoavoidhazardoussituationsinfactoryrooms（someautomakershaveestablishedcommunicationnetworkswhichregularlycheckprogramsinPLCcontrollerstoensureexecutiononlyofgoodprograms）.

AlmosteveryprogramforprogrammingaPLCcontrollerpossessesvarioususefuloptionssuchas:

forcedswitchingonandoffofthesysteminput/outputs（I/Olines）,programfollowupinrealtimeaswellasdocumentingadiagram.Thisdocumentingisnecessarytounderstandanddefinefailuresandmalfunctions.Programmercanaddremarks,namesofinputoroutputdevices,andcommentsthatcanbeusefulwhenfindingerrors,orwithsystemmaintenance.Addingcommentsandremarksenablesanytechnician（andnotjustapersonwhodevelopedthesystem）tounderstandaladderdiagramrightaway.Commentsandremarkscanevenquotepreciselypartnumbersifreplacementswouldbeneeded.Thiswouldspeeduparepairofanyproblemsthatcomeupduetobadparts.Theoldwaywassuchthatapersonwhodevelopedasystemhadprotectionontheprogram,sonobodyasidefromthispersoncouldunderstandhowitwasdone.Correctlydocumentedladderdiagramallowsanytechniciantounderstandthoroughlyhowsystemfunctions.

Electricalsupplyisusedinbringingelectricalenergytocentralprocessingunit.MostPLCcontrollersworkeitherat24VDCor220VAC.OnsomePLCcontrollersyou’llfindelectricalsupplyasaseparatemodule.ThoseareusuallybiggerPLCcontrollers,whilesmallandmediumseriesalreadycontainthesupplymodule.UserhastodeterminehowmuchcurrenttotakefromI/Omoduletoensurethatelectricalsupplyprovidesappropriateamountofcurrent.Differenttypesofmodulesusedifferentamountsofelectricalcurrent.

Thiselectricalsupplyisusuallynotusedtostartexternalinputoroutput.UserhastoprovideseparatesuppliesinstartingPLCcontrollerinputsbecausethenyoucanensuresocalled“pure”supplyforthePLCcontroller.Withpuresupplywemeansupplywhereindustrialenvironmentcannotaffectitdamagingly.SomeofthesmallerPLCcontrollerssupplytheirinputswithvoltagefromasmallsupplysourcealreadyincorporatedintoaPLC.

3.TheproblemsofPLC

PLC（programmablelogicalcontroller）faceevermorecomplexchallengethesedays.Whereoncetheyquietlyrelaysandgaveanoccasionalreporttoacorporatemainframe,theyarenowgroundedintocells,givenewjobsandnewlanguages,andareforcedtocompeteagainstagrowingarrayofcontrolproducts.

HigherlevelPLCprogramminglanguageshavebeenaroundforsometime,butlatelytheirpopularityhasbeenmushrooming.AsRaymondLavelle,vicepresidentandgeneralmanager,Siemensenergyandautomation.Inc,ProgrammableControlsDivision,pointsout:

”Asprogrammablecontrolsisbeingusedformoreandmoresophisticatedoperations,languagesotherthanladderlogicbecomemorepractical,efficient,andpowerful.Forexample,it'sverydifficulttowriteatrigonometricfunctionusingladderlogic.”LanguagesgainingacceptanceincludeBoolean,controlsystemflowcharting,andsuchfunctionchartlanguagesasGraphtecanditsvariations.AndtheseareincreasinginterestinlanguageslikeCandBASIC.

Thesoftwareindustryisregardedasaperformancedestructorandcomplexitygenerator.Steadilyshrinkinghardwarepricesspoilstheneedforsoftwareperformanceintermsofcodeoptimizationandefficiency.Theresultisthatmassiveandlessefficientsoftwarecodeononehandoutpacesthegainsinhardwareperformanceontheotherhand.Secondly,softwareproliferatesintocomplexityofunmanageabledimensions;softwareredesignandmaintenance-essentialinmodernautomationsystems-becomesnearlyimpossible.Particularly,PLCprogramshaveevolvedfromacouplelinesofcode25yearsagotothousandsoflinesofcodewithasimilarnumberof1/Opoints.Increasedsafety,forinstancenewpoliciesonfireprotectionandtheflexibilityofmodernautomationsystemsaddcomplexitytotheprogramd