王曦英文翻译最终版.docx

王曦英文翻译最终版.docx

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王曦英文翻译最终版

PROGRAMMABLE

LOGICCONTROLLER

ABSTRACT

Industrialautomationisthenowvitalforitsprosperity,sinceitreducestheproductioncostmanyfoldsandalsoincreasesproductivity.ForthispurposeWLC（i.e.WiredLogicController）wasintroducedin60s-70s.Itwasthefirststepintheindustrialautomation.LateronmicrocontrollerswereintroducedwhichhadtheadvantageofgreaterflexibilityovertheWLC.Withtheevolutionoftechnology,averysophisticatedversionofacontrollerwasintroducedwithaverylargeI/OhandlingcapabilityandextremeflexibilitycalledtheProgrammableLogicController,commonlycalledthePLC.

ThePLCsarenotalientotheindustriesofPakistan.Theyhavebeenaroundforquitealongperiodandarebeingemployedextensively.Eventhoughthedemandofthisproductisconsiderablehere,therehasbeennoefforttodevelopitindigenously.Sincetherehadbeennodevelopmentinthisfieldinourcountryandbeingarequisiteofthenation,soasanexerciseofLogicDesign,DigitalElectronics,InterfacingandSoftwareEngineering.Aspartofourcoursework,wehavetoundertakeaprojectinthefinalsemester.ThisarticledescribesthedesignandimplementationprocessofaProgrammableLogicController（PLC）,inthatconnection.Thetaskwasundertakenasanexerciseindigitalcircuitdesign,microcontrollerapplicationandinterfacesincewealreadyhadtakenupprojectsrelatedtopowerandanalogelectronicsinprecedingsemesters.

Keywords:

ProgrammableLogicController（PLC）,Automation,MicrocontrollerApplications,IndustrialElectronics,DigitalControl,On-OffControl,DigitalElectronics

1.INTRODUCTION

1.1PROBLEMDESCRIPTION

Weallknowthatindustrialautomationisthebackboneofanationforitsprosperitysince,itreducestheproductioncostmanyfoldsandalsoincreasesproductivity.ForthispurposeWLC（i.e.WiredLogicController）wasintroduced.Itwasthefirststepintheindustrialautomation.LateronmicrocontrollerswereintroducedwhichhadtheadvantageofgreaterflexibilityovertheWLC.

Eventually,averysophisticatedversionofacontrollerwasintroducedwithaverylargeI/OhandlingcapabilityandextremeflexibilitycalledtheProgrammableLogicController,commonlycalledthePLC.Siemensintroducedmanyseriesofcontrollerswithdifferentcapabilities.OneofthefirstserieswastheSIMATIC®5Controllers.ThePLCavailabletousistheS5-100U-100.LateronSiemensintroducedtheSIMATIC®7seriesofcontrollersandnow,wealsohavetheS7-314IFMPLC.

ThePLCsarenotalientotheindustriesofPakistan.Theyhavebeenaroundforquitealongperiodandarebeingemployedextensively.Eventhoughthedemandofthisproductisconsiderablehere,therehasbeennoefforttodevelopitindigenously.Sincetherehadbeennodevelopmentinthisfieldinourcountryandbeingarequisiteofthenation,soasanexerciseofLogicDesign,DigitalElectronics,InterfacingandSoftwareEngineering,weundertookthistaskofmakingaPLCbetterthantheS5controllersandcomparabletosomeextenttotheS7controllers.ThePLCthatwehavedesignedcanalsobeupgradedtosupport

RemoteDataAcquisition.

1.2BLOCKDIAGRAMANDBRIEFDESCRIPTION

ThecompletegeneralblockdiagramofthePLCisdepictedinFig.1-1.JustliketheSIMATIC®5systems,ourPLCcanalsobebroadlyclassifiedintothreedistinctunits:

a.CPU

b.Busunit,and

c.Modules（I/Oandfunction）

Fig.1-1BlockdiagramofthePLC

Eachunitcanbediscussedasfollows:

1.2.1CPU

TheCPU,asthenamesuggests,isthebrainofthePLCsystem.Withoutitsbrain,thePLCsimplycannotfunction.

Inoursystem,theCPUcomprisesoftwoATMEL®89C52microcontrollers.Asineverymultiprocessorsystem,oneisthemasterandtheotheristheslave.Thefunctionsperformedbythemasterorthecontrollingunit（Fig.1-1）canbesummarizedasfollows:

∙MonitorandcontroltheoperatingmodesofthePLCusingtheoperationcontrols.

∙ConfigurethePLCmodules.

∙Checkprogramintegritybymonitoringscancycles.

Theslavemicrocontroller（executingunit,Fig.1-1）functionstoruntheuserprogram.Itisresponsiblefor:

∙Takingtheappropriateactionsduringstartup.

∙Issuingthe

signalatthestartofeveryscancycleandthesubsequent

addressingandtransactionofdatawiththemodules.

∙Handlingthecountersandtimers.

TheCPUsectionalsohastheresponsibilityofcommunicatingtheprogrammingdevicei.e.thecomputerthroughaserialport.Thecommunicationchannelworksaccordingtothesemaphorealgorithm（commonlyknownastokenalgorithm）.Itistobenotedherethatthecommunicationlinkcurrentlydoesnotfunction,asmentionedearlier,becauseitwasapartoftheplannedGUI,whichhasnotbeenimplementedduetotheconstraintoftime.

1.2.2BUSUNIT

Thebusunitfunctionssimilartothemotherboardinacomputer.Thebusunitthatwehaveconstructedholdsupto4modulesandtheCPU;wenameditthemainbusunit.Moreover,thebusunitalsocarriestheextensionconnectorbywhichotherbusunitscanbecascadedtoincreasetheI/OhandlingcapabilityofthePLC.ThebusunitsthatwillbecascadedwillnothaveaslotforconnectingtheCPU;onlymodulescanbeconnected.

Themainfunctionofthebusunitistobufferallthesignalsi.e.thedatabuses,addressbuses,andthecontrolsignals,toeliminatetheloadingoftheCPU.Thisfunctionisalsoperformedbythemainbusunitbutthisalsoperformsanextrafunctionduringtheconfigurationstage.Thebusunitcontroller,seeFig.1-1,selectseachslotoneatatimesothatitcanbeconfiguredforthemoduleconnectedinitandalsosendsasignaltothecontrollingunitwhenalltheslotshavebeenselectedandconfiguredonce.

1.2.3MODULES

ThemodulesservetoprovidetheinterfaceofthePLCwiththeplanttobecontrolled.Themodules,whichwehaddesignedweredigitalinput,digitaloutput,analoginputandanalogoutputmodules（verifiedusingOrCAD®PSpice）.Butweonlymanagedtomanufacturethedigitalinputandoutputmodules,eachcapableofhandling16devices.Thestandardsofthemodulesaresimilartothatofcommerciallyavailablemodules.

Themodulesareequippedwithanaddressdecodercircuit,whichiscommoninallthemodules,asthecircuithasbeendesignedtosupportautoconfiguration.

1.3POSSIBLESOLUTIONS

Nowthattheoverviewoftheprojectispresentbeforeus,wewilltakealookintothepossiblesolutionsthatcametoourmindwhenwecommencedbrainstorming.Theideascanbelistedasfollowsalongwiththeirsupportinganddisagreementcomments.

∙Useofasingleprocessor/microcontrollerwasthefirstideathatcametomind

becauseitwasmostsimpleandeasytoimplement.Theproblemwithsuchanideawasthatwewerestrivingforagoodscantimeduetowhichweneededafastprocessor（whichwasunavailable）orhadtogoformultipleprocessors.

∙Theuseofmicroprocessorinsteadofamicrocontrollerwasalsoamongtheoptionsbecausewehavebeentaughttheassemblylanguageofthisprocessorandwewerewellawareofit.ThedrawbackofsuchaselectionwasthatinaPLC,bitoperationsareplentywhilethemicroprocessorinstructionisnotverypowerfulforsuchoperations.

∙Usinga16-bitmicrocontrollerforeaseofworkwasagreatideabutitsmaterializationwasnotpossibleasitwasnotavailablehere.

∙Afteralltheseoptions,wewereleftonlywiththeoptionofusingtwomicrocontrollersintandemtoachieveourdesiredtask.

1.4REASONSFORSELECTION

Ofalltheabovesolutionsmentionedabove,wedecidedtoimplementthemultiprocessorCPUwiththebusunitschemeforconnectingthemodules.Theadvantages,whichalsoformthereasonsfortheselectionofthisdesign,areenumeratedbelow.

∙Thissolutionwasthefirstseeminglyfeasiblesolutionthatcametoourminds.Duringthecourseofwork,manymorecamebutthenitwastoolate.

∙Thedesignwasbasedonequipmentandtechnologyeasilyavailableinourcity.

∙Theuseofmicrocontrollerinsteadofamicroprocessorisjustifiedbythefactthatthemicroprocessorisincapableofbitoperations,whicharenumerousinaPLC.

∙Afastmicrocontrollerwasunavailablehencewedecidedtodistributetheworkloadandruntaskssimultaneouslybyusingtwocontrollerssothatthespeedisnotcompromised.

∙Theautoconfigurationfeatureallowsthedesignofthemodulestobequitegenericastheaddressdecodingsectionisidenticalhenceensuringeaseofmanufacture.

∙TheuseofthebusunitallowscosteffectivenessasspecializedcircuitsineachmodulearenotrequiredasfoundintheSIMATIC®7controllers.

2.ANALYSISANDSIMULATION

Sinceoursystemisadigitalsystembasedonmicrocontrollers,itwasnotpossibletoobtainitsmathematicalmodel.Instead,wehavesimulatedourcircuitdesignwithallthereallifelimitationsinOrCAD®9.1PSpice.Thecomputerhardwaresimulationresultsandtheiranalysisarediscussedbelow.

2.1COMPUTERSIMULATIONS-HARDWARE

Thesimulationswerecarriedindifferentstages;theautoconfigurationprocess,inwhichthecontrolwordisreadandthentheappropriateaddress,isassignedtothemodule.Oncethiswastested,thecompletesequenceofreadingdatafromadigitalinputmodulewastested.Similarly,thesequenceofwritingtoadigitaloutputmodulewasalsotested.

Beforediscussingtheprocesses,onethingthatmustbestressedisthatthesignalsusedfortestingtheperformanceofthecircuitswereconstructedusingactualtimingdelaysthatwouldbeintroducedbythemicrocontrollers.Allthepropagationdelays,pulsewidths,etc.havebeencarefullyimplementedsothatoursimulationsareasneartopracticalresultsaspossible.

2.1.1THEAUTOCONFIGURATIONP