PLC外文文献翻译文档格式.docx

PLC外文文献翻译文档格式.docx

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自动化工程 学院电气工程及其自动化专业 082班

2012年6 月12 日

目录

ProgrammableLogicController（PLC） 1

1.AboutProgrammableLogicController（PLC） 1

2.INTRODUCTION 2

3.OPERATIONSEQUENCE 4

3.1TheInputandOutputScans 5

3.2TheLogicScan 5

4PLCSTATUS 6

5.MEMORYTYPES 7

6.SOFTWAREBASEDPLCS 8

7.SUMMARY 8

8.PRACTICEPROBLEMS 8

9.PRACTICEPROBLEMSOLUTIONS 9

中文翻译 11

1.PLC介绍 11

2．指令 12

3.运行顺序 13

3.1输入输出扫描 14

3.2逻辑扫描 14

4.PLC状态显示 15

5.存储器类型 16

6.基于软件的PLC系统 16

7．概要 17

8.实际问题 17

9.实际问题解答 17

ProgrammableLogicController（PLC）

1.AboutProgrammableLogicController（PLC）

PLC（programmablelogiccontrollers）isthecontrolhubsforawidevarietyofautomatedsystemsandprocesses.Theycontainmultipleinputsandoutputsthatusetransistorsandothercircuitrytosimulateswitchesandrelaystocontrolequipment.Theyareprogrammableviasoftwareinterfacedviastandardcomputerinterfacesandproprietarylanguagesandnetworkoptions.

ProgrammablelogiccontrollersI/Ochannelspecificationsincludetotalnumberofpoints,numberofinputsandoutputs,abilitytoexpand,andmaximumnumberofchannels.Numberofpointsisthesumoftheinputsandtheoutputs.PLCmaybespecifiedbyanypossiblecombinationofthesevalues.Expandableunitsmaybestackedorlinkedtogethertoincreasetotalcontrolcapacity.Maximumnumberofchannelsreferstothemaximumtotalnumberofinputandoutputchannelsinanexpandedsystem.PLCsystemspecificationstoconsiderincludescantime,numberofinstructions,datamemory,andprogrammemory.ScantimeisthetimerequiredbythePLCtocheckthestatesofitsinputsandoutputs.Instructionsarestandardoperations（suchasmathfunctions）availabletoPLCsoftware.Datamemoryisthecapacityfordatastorage.Programmemoryisthecapacityforcontrolsoftware.

AvailableinputsforprogrammablelogiccontrollersincludeDC,AC,analog,thermocouple,RTD,frequencyorpulse,transistor,andinterruptinputs.OutputsforPLCincludeDC,AC,relay,analog,frequencyorpulse,transistorandtriac.ProgrammingoptionsforPLCincludefrontpanel,handheldandcomputer.

Programmablelogiccontrollersuseavarietyofsoftwareprogramminglanguagesforcontrol.TheseincludeIEC61131-3,sequentialfunctionchart（SFC）,functionblockdiagram（FBD）,ladderdiagram（LD）,structuredtext（ST）,instructionlist（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（PLC）.Ladderlogicprogrammingisagraphicalrepresentationoftheprogramdesignedtolooklikerelaylogic.FlowChartisagraphicallanguagethatdescribessequentialoperationsinacontrollersequenceorapplication.Itisusedtobuildmodular,reusablefunctionlibraries.Cisahighlevelprogramminglanguagesuitedtohandlethemostcomplexcomputation,sequential,anddataloggingtasks.ItistypicallydevelopedanddebuggedonaPC.BASICisahighlevellanguageusedtohandlemathematical,sequential,datacapturingandinterfacefunctions.Programmablelogiccontrollerscanalsobespecifiedwithanumberofcomputerinterfaceoptions,networkspecificationsandfeatures.PLCpoweroptions,mountingoptionsandenvironmentaloperatingconditionsareallalsoimportanttoconsider.

2.INTRODUCTION

ForsimpleprogrammingtherelaymodelofthePLCissufficient.AsmorecomplexfunctionsareusedthemorecomplexVonNeumanmodelofthePLCmustbeused.AVonNeumancomputerprocessesoneinstructionatatime.Mostcomputersoperatethisway,althoughtheyappeartobedoingmanythingsatonce.ConsiderthecomputercomponentsshowninFigure1.

Figure1 SimplifiedPersonalComputerArchitecture

Inputisobtainedfromthekeyboardandmouse,outputissenttothescreen,andthediskandmemoryareusedforbothinputandoutputforstorage.（Note:

thedirectionsofthesearrowsareveryimportanttoengineers,alwayspayattentiontoindicatewhereinformationisflowing.）ThisfigurecanberedrawnasinFigure2toclarifytheroleofinputsandoutputs.

Figure2 AnInput-OutputOrientedArchitecture

Inthisfigurethedataenterstheleftsidethroughtheinputs.（Note:

mostengineeringdiagramshaveinputsontheleftandoutputsontheright.）IttravelsthroughbufferingcircuitsbeforeitenterstheCPU.TheCPUoutputsdatathroughothercircuits.Memoryanddisksareusedforstorageofdatathatisnotdestinedforoutput.Ifwelookatapersonalcomputerasacontroller,itiscontrollingtheuserbyoutputtingstimulionthescreen,andinputtingresponsesfromthemouseandthekeyboard.

APLCisalsoacomputercontrollingaprocess.Whenfullyintegratedintoanapplicationtheanalogiesbecome;

Inputs-thekeyboardisanalogoustoaproximityswitch

Input-circuits-theserialinputchipislikea24VdcinputcardComputer-the686CPUislikeaPLCCPUunit

Output-circuits-agraphicscardislikeatriacoutputcardOutputs-amonitorislikealight

Storage-memoryinPLCissimilartomemoriesinpersonalcomputers

ItisalsopossibletoimplementaPLCusinganormalPersonalComputer,althoughthisisnotadvisable.InthecaseofaPLCtheinputsandoutputsaredesignedtobemorereliableandruggedforharshproductionenvironments.

3.OPERATIONSEQUENCE

AllPLCshavefourbasicstagesofoperationsthatarerepeatedmanytimespersecond.Initiallywhenturnedonthefirsttimeitwillcheckit’sownhardwareandsoftwareforfaults.Iftherearenoproblemsitwillcopyalltheinputandcopytheirvaluesintomemory,thisiscalledtheinputscan.Usingonlythememorycopyoftheinputstheladderlogicprogramwillbesolvedonce,thisiscalledthelogicscan.Whilesolvingtheladderlogictheoutputvaluesareonlychangedintemporarymemory.Whentheladderscanisdonetheoutputswillbeupdatedusingthetemporaryvaluesinmemory,thisiscalledtheoutputscan.ThePLCnowrestartstheprocessbystartingaselfcheckforfaults.Thisprocesstypicallyrepeats10to100timespersecondasisshowninFigure3.

Figure3 PLCScanCycle

SELFTEST-Checkstoseeifallcardserrorfree,resetwatch-dogtimer,etc.（Awatchdogtimerwillcauseanerror,andshutdownthePLCifnotresetwithinashortperiodoftime-thiswouldindicatethattheladderlogicisnotbeingscannednormally）.

INPUTSCAN-Readsinputvaluesfromthechipsintheinputcards,andcopiestheirvaluestomemory.ThismakesthePLCoperationfaster,andavoidscaseswhereaninputchangesfromthestarttotheendoftheprogram（e.g.,anemergencystop）.TherearespecialPLCfunctionsthatreadtheinputsdirectly,andavoidtheinputtables.

LOGICSOLVE/SCAN-Basedontheinputtableinmemory,theprogramisexecuted1stepatatime,andoutputsareupdated.Thisisthefocusofthelatersections.

OUTPUTSCAN-Theoutputtableiscopiedfrommemorytotheoutputchips.

Thesechipsthendrivetheoutputdevices.

Theinputandoutputscansoftenconfusethebeginner,buttheyareimportant.Theinputscantakesasnapshotoftheinputs,andsolvesthelogic.Thisprevents

potentialproblemsthatmightoccurifaninputthatisusedinmultipleplacesintheladderlogicprogramchangedwhilehalfwaysthroughaladderscan.Thuschangingthebehaviorsofhalfoftheladderlogicprogram.Thisproblemcouldhavesevereeffectsoncomplexprogramsthataredevelopedlaterinthebook.Onesideeffectoftheinputscanisthatifachangeininputistooshortinduration,itmightfallbetweeninputscansandbemissed.

WhenthePLCisinitiallyturnedonthenormaloutputswillbeturnedoff.Thisdoesnotaffectthevaluesoftheinputs.

3.1TheInputandOutputScans

WhentheinputstothePLCarescannedthephysicalinputvaluesarecopiedintomemory.WhentheoutputstoaPLCarescannedtheyarecopiedfrommemorytothephysicaloutputs.Whentheladderlogicisscanneditusesthevaluesinmemory,nottheactualinputoroutputvalues.Theprimaryreasonfordoingthisissothatifaprogramusesaninputvalueinmultipleplaces,achangeintheinputvaluewillnotinvalidatethelogic.Also,ifoutputbitswerechangedaseachbitwaschanged,insteadofallatonceattheendofthescanthePLCwouldoperatemuchslower.

3.2TheLogicScan

Ladderlogicprogramsaremodelledafterrelaylogic.Inrelaylogiceachelementintheladderwillswitchasquicklyaspossible.Butinaprogramelementscanonlybeexaminesoneatatimeinafixedsequence.ConsidertheladderlogicinFigure4,theladderlogicwillbeinterpretedleft-