外文文献翻译可编程逻辑控制器PLC.docx

外文文献翻译可编程逻辑控制器PLC.docx

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外文文献翻译可编程逻辑控制器PLC

可编程逻辑控制器PLC外文文献翻译

（含：

英文原文及中文译文）文献出处：

KinnaD.ProgrammableLogicControllers（PLC）[J].FusionEngineering&Design,2015,2（12）:

72-83.

英文原文

ProgrammableLogicControllers（PLC）

KinnaDari

1Motivation

ProgrammableLogicControllers（PLC）,acomputingdeviceinventedbyRichardE.Morleyin196&havebeenwidelyusedinindustryincludingmanufacturingsystems,transportationsystems,chemicalprocessfacilities,andmanyothers.Atthattime,thePLCreplacedthehardwiredlogicwithsoft-wiredlogicorso-calledrelayladderlogic（RLL）,aprogramminglanguagevisuallyresemblingthehardwiredlogic,andreducedtherebytheconfigurationtimefrom6monthsdownto6days[MoodyandMorley,1999].

AlthoughPCbasedcontrolhasstartedtocomeintoplace,PLCbasedcontrolwillremainthetechniquetowhichthemajorityofindustrialapplicationswilladhereduetoitshigherperformance,lowerprice,andsuperiorreliabilityinharshenvironments・Moreover,accordingtoastudyonthePLCmarketofFrostandSullivan[1995],anincreaseoftheannualsalesvolumeto15millionPLCsperyearwiththehardwarevalueofmorethan8billionUSdollarshasbeenpredicted,thoughthepricesofcomputinghardwareissteadilydropping.TheinventorofthePLC,RichardEMorley,fairlyconsidersthePLCmarketasa5-billionindustryatthepresenttime.

Ingeneral,theproductivityingeneratingPLCisfarbehindcomparedtootherdomains,forinstance,VLSIdesign,whereefficientcomputeraideddesigntoolsareinpractice・ExistentsoftwareengineeringmethodologiesarenotnecessarilyapplicabletothePLCbasedsoftwaredesignbecausePLC-programmingrequiresasimultaneousconsiderationofhardwareandsoftware・Thesoftwaredesignbecomes,thereby,moreandmorethemajorcostdriver.Inmanyindustrialdesignprojects,morethan50%ofthemanpowerallocatedforthecontrolsystemdesignandinstallationisscheduledfortestinganddebuggingPLCprograms[Rockwell,1999].

PLCs（programmablelogiccontrollers）arethecontrolhubsforawidevarietyofautomatedsystemsandprocesses.Theycontainmultipleinputsandoutputsthatusetransistorsandothercircuitrytosimulateswitchesandrelaystocontrolequipment.Theyareprogrammableviasoftwareinterfacedviastandardcomputerinterfacesandproprietarylanguagesandnetworkoptions・

ProgrammablelogiccontrollersI/Ochannelspecificationsincludetotalnumberofpoints,numberofinputsandoutputs,abilitytoexpand,andmaximumnumberofchannels・Numberofpointsisthesumoftheinputsandtheoutputs・PLCsmaybespecifiedbyanypossiblecombinationofthesevalues.Expandableunitsmaybestackedorlinkedtogethertoincreasetotalcontrolcapacity.Maximumnumberofchannelsreferstothemaximumtotalnumberofinputandoutputchannelsinanexpandedsystem・

PLCsystemspecificationstoconsiderincludescantime,numberofinstructions,datamemory,andprogrammemory.ScantimeisthetimerequiredbythePLCtocheckthestatesofitsinputsandoutputs.Instructionsarestandardoperations（suchasmathfunctions）availabletoPLCsoftware.Datamemoryisthecapacityfordatastorage・Programmemoryisthecapacityforcontrolsoftware.

Programmablelogiccontrollersuseavarietyofsoftwareprogramminglanguagesforcontrol.TheseincludeIEC61131-3,sequentialfunctionchart（SFC）,functionblockdiagram（FBD）,ladderdiagram（LD）,structuredtext（ST）,insti-uctionlist（IL）,relayladderlogic（RLL）,flowchart,C,andBasic.TheIEC61131-3programmingenvironmentprovidessupportforfivelanguagesspecifiedbytheglobalstandard:

SequentialFunctionChart,FunctionBlockDiagram,LadderDiagram,StructuredText,andInstructionList.Thisallowsformulti-vendorcompatibilityandmulti-languageprogramming.SFCisagraphicallanguagethatprovidescoordinationofprogramsequences,supportingalternativesequenceselectionsandparallelsequences.FBDusesabroadfunctionlibrarytobuildcomplexproceduresinagraphicalformat・Standardmathandlogicfunctionsmaybecoordinatedwithcustomizablecommunicationandinterfacefunctions.LDisagraphiclanguagefordiscretecontrolandinterlockinglogic.ItiscompletelycompatiblewithFBDfordiscretefunctioncontrol.STisatextlanguageusedforcomplexmathematicalproceduresandcalculationslesswellsuitedtographicallanguages.ILisalow-levellanguagesimilartoassemblycode・Itisusedinrelativelysimplelogicinstructions.RelayLadderLogic（RLL）,orladderdiagrams,istheprimaryprogramminglanguageforprogrammablelogiccontrollers（PLCs）・Ladderlogicprogrammingisagraphicalrepresentationoftheprogramdesignedtolooklikerelaylogic.FlowChartisagraphicallanguagethatdescribessequentialoperationsinacontrollersequenceorapplication.Itisusedtobuildmodular,reusablefunctionlibraries.Cisahighlevelprogramminglanguagesuitedtohandlethemostcomplexcomputation,sequential,anddataloggingtasks.ItistypicallydevelopedanddebuggedonaPC.BASICisahighlevellanguageusedtohandlemathematical,sequential,datacapturingandinterfacefunctions・

2Resume

APLC（programmableLogicController）isadevicethatwasinventedtoreplacethenecessarysequentialrelaycircuitsforcontrol.ThePLCworksbylookingatitsinputanddependingupontheirstate,turningon/offitsoutputs・Theuserentersaprogram,usuallyviasoftwareorprogrammer,whichgivesthedesiredresults.

PLCisusedinmanyurealworldHapplications.Ifthereisindustrypresent,chancearegoodthatthereisaPLCpresent.Ifyouareinvolvedinmachining,packing,materialhandling,automatedassemblyorcountlessotherindustries,youareprobablyalreadyusingthem.Ifyouarenot,youarewastingmoneyandtime・AlmostanyapplicationthatneedssometypeofelectricalcontrolhasaneedforaPLC・

Forexample,let'sassumethatwhenaswitchturnsonwewanttoturnasolenoidonfor5secondandthenturnitoffregardlessofhowlongtheswitchisonfor.Wecandothiswithasimpleexternaltimer.Butwhatiftheprocessincluded10switchesandsolenoids?

Weshouldneed10externaltimes・Whatiftheprocessalsoneededtocounthowmanytimestheswitchindividuallyturnedon?

Weneedalotofexternalcounters.

AsyoucanseethebiggertheprocessthemoreofaneedwehaveforaPLC・WecansimplyprogramthePLCtocountitsinputandturnthesolenoidsonforthespecifiedtime.WewilltakealookatwhatisconsideredtobetheHtop20"PLCinstructions.Itcanbesafelyestimatedthatwithafirmunderstandingoftheseinstructionsonecansolvemorethan80%oftheapplicationsinexistence・

OfcoursewewilllearnmorethanjustthisinstructiontohelpyousolvealmostALLpotentialPLCapplications.

ThePLCmainlyconsistsofaCPU,memoryareas,andappropriatecircuitstoreceiveinput/outputdata.WecanactuallyconsiderthePLCtobeaboxfullofhundredsorthousandsofseparaterelay,counters,timesanddatastoragelocations,Dothesecounters,timers,etc.reallyexist?

No,theydon't“physically"existbutrathertheysimulatedandbeconsideredsoftwarecounters,timers,etc.・Theseinternalrelaysaresimulatedthroughbitlocationsinregisters.

Whatdoeseachpartdo?

Letmetellyou.

InputRelays

Theseareconnectedtotheoutsideworld.Theyphysicallyexistandreceivesignalsfromswitches,sensors.Typicallytheyarenotrelaysbutrathertheyaretransistors・

InternalUtilityRelays

Thesedonotreceivesignalsfromtheoutsideworldnordotheyphysicallyexist,theyaresimulatedrelaysandarewhatenablesaPLCtoeliminateexternalrelays・Therearealsosomespecialrelaysthatarededicatedtoperformingonlyonetask.Somearealwaysonwhilesomearealwaysoff.Someareononlyonceduringpower-onandaretypicallyusedforinitializingdatathatwasstored.

Counters

Theseagaindonotphysicallyexist.Theyaresimulatedcountersandtheycanbeprogrammedtocountpulses.Typicallythesecounterscancountup,downorbothupanddown.Sincetheyaresimulated,theyarelimitedintheircountingspeed・Somemanufacturersalsoincludehigh-speedcountersthatarehardwarebased.Wethinkoftheseasphysicallyexisting.Mosttimesthesecounterscancountup,downorupanddown.

Timers

Thesealsodonotphysicallyexist.Theycomeinmanyvarietiesandincrements.Themostcommontypeisanon-delaytype.Othersincludeoff-delaysandbothretentiveandnon-retentivetypes・Incrementsvaryfrom1msthroughIs.

OutputRelays

Thereareconnectedtotheoutsideworld.Theyphysicallyexistandsendon/offsignalstosolenoids,lights,etc.Theycanbetransistors,relays,ortriacsdependinguponthemodelchosen.DataStorage

Typicallythereareregistersassignedtosimplystoredata.Theyareusuallyusedastemporarystorageformathordatamanipulation.TheycanalsotypicallybeusedtostoredatawhenpowerisremovedformthePLC・Uponpower-uptheywillstillhavethesamecontentsasbeforepowerwasmoved.Veryconvenientandnecessary!

APLCworksbycontinuallyscanningaprogram・Wecanthinkofthisscancycleasconsistingof3importantsteps.Therearetypicallymorethan3butwecanfocusontheimportantpartsandnotworryabouttheothers,Typicallytheothersarecheckingthesystemandupdatingthecurrentinternalcounterandtimervalues・

Step1istocheckinputstatus,FirstthePLCtakesalookateachinputtodetermineifitisonoff.Inotherwords,isthesensorconnectedtothefirstinputon?

Howaboutthethird...Itrecordsthisdataintoitsmemorytobeusedduringthenextstep.

Step2istoexecuteprogram.NextthePLCexecutesyourprogramoneinstructionatatime.Maybeyourprog