电气工程及自动化文献综述 (26).doc

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1、 中国地质大学长城学院本科毕业论文文献综述学 院工程技术学院学生姓名陈瑀专 业电气工程及其自动化学 号0431301442017 年 4 月 20 日第12页 共13页外文资料PLCtechniquediscussionandfuturedevelopmentWrite by T. J. byersFrom: Electronic Test Equipment-principles and Applications. Princeton University. America.Alongwiththedevelopmentoftheages,thetechniquethatisnowadays

2、isalsograduallyperfect,thecompetitionplaysmorestrong;theoperationthatlistdependstheartificialhasalreadycantsatisfiedwiththecurrentmanufacturingindustryforeground,alsocantguaranteetherequestofthehigherquantityandhighnewtheimageofthetechniquebusinessenterprise.Thepeopleseeinproducepractice,automatebro

3、ughtthetremendousconvenienceandtheproductquantitiesforpeopleupofassurance,alsoeasedthepersonnelslaborstrength,reducetheestablishmentonthepersonnel.Thetargetcontrolofthehardrealizationinmanycomplicatedproductionlines,wholeandexcellentturn,thebestdecisionetc.,well-trainedoperationwork,technicalpersonn

4、elorexpert,governorbutcanjudgeandoperateeasily,canacquirethesatisfiedresult.Theresearchtargetoftheartificialintelligencemakesuseofthecalculatorexactlytocarryout,imitatetheseintelligencesbehavior,moderatingtheworkthroughpersonsbrainandcalculators,withthemodethatpersonsmachinecombine,forresolvethevery

5、complicatedproblemtolookforthebestpathWe come in sight of the control that links after the electric appliances in various situation, that is already the that time generation past, now of after use in the mold a perhaps simple equipments of grass-roots control that the electric appliances can do for

6、the low level only; And the PLC emergence also became the epoch-making topic, adding the vivid software control through a very and stable hardware, making the automation head for the new high tide. The PLC biggest characteristics lie in: The electrical engineering teacher already no longer electric

7、hardware up too many calculations of cost, as long as order the importation that the button switch or the importation of the sensors order to link the PLC up can solve problem, pass to output to order the conjunction contact machine or control the start equipments of the big power after the electric

8、 appliances, but the exportation equipments direct conjunction of the small power can.PLCinternalcontainmenthavetheCPUoftheCPU,andtaketohaveanI/Oforexpandofexteriortoconnectapeoplesaddressandsavingmachinethreebigpiecestoconstitute,CPUcoreisfromanormanyistiredtoaddthemachinetoconstitute,mathematicsth

9、attheyhavethelogicoperationability,andcanreadtheproceduresavethecontentsofthemachinetodrivethehomologoussavingmachineandI/Ostoconnectafterpassthecalculation;TheI/Oaddinnerpartistiredtheinputandoutputsystemofthemachineandexteriorlink,anddeposittherelateddataintotheproceduresavingmachineordatasavingma

10、chine;ThesavingmachinecandepositthedatathattheI/Oinputinthesavingmachine,andinworkadjustingto become tired to add the machine and I/ Os to connect, saving machine separately saving machine RAM of the procedure saving machine ROM and dates, the ROM can do deposit of the data permanence in the saving

11、machine, but RAM only for the CPU computes the temporary calculation usage of hour of buffer space.ThePLCanti-interferenceisveryandexcellent,ourrootneednotconcernitsservicelifeandtheworksituationbad,theseallproblemshavealreadynolongerbecomethetopicthatwefail,butstaytoourisaconcerntocometointernalres

12、ourcesofmakeuseofthePLCtostrengthenthecontrolabilityoftheequipmentsforus,makeourequipmentsmoregentle.PLClanguageisnotweimagineofeditcollectedmaterialsthelanguageorlanguageofCstocarryonweavingthedistance,butthetrapezoiddiagramthattheadoptionisoriginalaftertheelectricappliancestocontrol,maketheelectri

13、calengineeringteacherwhileweavingtowritetheprocedureveryeasycomprehendedthePLClanguage,andalotofnon-electricityprofessionalalsoveryquicklyknowandgodeepintotothePLC.TounderstandthePLCscommunicationsversatility,letsfirstdefinethetermsusedindescribingthevarioussystems.ASCII:ThisstandsforAmericanStandar

14、dCodeforInformationInterchange.AsshowninFig.1,whentheletterAistransmitted,forinstance,itsautomaticallycodedas65bythesendingequipment.Thereceivingequipmenttranslatesthe65backtotheletterA.Thus,differentdevicescancommunicatewitheachotheraslongasbothuseASCIIcode.ASCIImodule:ThisintelligentPLCmoduleisuse

15、dforconnectingPLCstootherdevicesalsocapableofcommunicatingusingASCIIcodeasavehicle.Bustopology:Thisisalinearlocalareanetwork(LAN)arrangement,asshowninFig.2A,inwhichindividualnodesaretappedintoamaincommunicationscableatasinglepointandbroadcastmessages.Thesemessagestravelinbothdirectionsonthebusfromth

16、epointofconnectionuntiltheyaredissipatedbyterminatorsateachendofthebus.CPU:Thisstandsforcentralprocessingunit,whichactuallyisthatpartofacomputer,PLC,orotherintelligentdevicewherearithmeticandlogicaloperationsareperformedandinstructionsaredecodedandexecuted.Daisychain:Thisisadescriptionoftheconnectio

17、nofindividualdevicesinaPLCnetwork,where,asshowninFig.3,eachdeviceisconnectedtothenextandcommunicationssignalspassfromoneunittothenextinasequentialfashion.Distributedcontrol:Thisisanautomationconceptinwhichportionsofanautomatedsystemarecontrolledbyseparatecontrollers,whicharelocatedincloseproximityto

18、theirareaofdirectcontrol(controlisdecentralizedandspreadout over the system).Hostcomputer:Thisisacomputerthatsusedtotransferdatato,orreceivedatafrom,aPLCinaPLC/computernetwork.Intelligentdevice:ThistermdescribesanydeviceequippedwithitsownCPU.I/O:Thisstandsforinputsandoutputs,whicharemodulesthathandl

19、edatatothePLC(inputs)orsignalsfromthePLC(outputs)toanexternaldevice.Kbps:Thisstandsforthousandbitspersecond,whichisarateofmeasureforelectronicdatatransfer.Mbps:Thisstandsformillionbitspersecond.Node:Thistermisappliedtoanyoneofthepositionsorstationsinanetwork.Eachnodeincorporatesadevicethatcancommuni

20、catewithallotherdevicesonthenetwork.Protocol:Thedefinitionofhowdataisarrangedandcodedfortransmissiononanetwork.Ringtopology.ThisisaLANarrangement,asshowninFig.2C,inwhicheachnodeisconnectedtotwoothernodes,resultinginacontinuous,closed,circularpathorloopformessagestocirculate,usuallyinonedirection.Som

21、eringtopologieshaveaspecialloopbackfeaturethatallowsthemtocontinuefunctioningevenifthemaincableissevered.RS232.ThisisanIEEEstandardforserialcommunicationsthatdescribesspecificwiringconnections,voltagelevels,andotheroperatingparametersforelectronicdatacommunications.TherealsoareseveralotherRSstandard

22、sdefined.Serial:Thisisanelectronicdatatransferschemeinwhichinformationistransmittedonebitatatime.Serialport:Thisthecommunicationsaccesspointonadevicethatissetupforserialcommunications.Startopology.ThisisaLANarrangementinwhich,asshowninFig.2B,nodesareconnectedtooneanotherthroughacentralhub,whichcanbe

23、activeorpassive.Anactivehubperformsnetworkdutiessuchasmessageroutingandmaintenance.Apassivecentralhubsimplypassesthemessagealongtoallthenodesconnectedtoit.Topology:ThisrelatestoaspecificarrangementofnodesinaLANinrelationtooneanother.Transparent:Thistermdescribesautomaticeventsorprocessesbuiltintoasy

24、stemthatrequirenospecialprogrammingorpromptingfromanoperator.Nowthatwerefamiliarwiththeseterms,letsseehowtheyareusedindescribingtheavailablePLCnetworkoptions.PLCnetworkoptionsPLCnetworksprovideyouwithavarietyofnetworkingoptionstomeetspecificcontrolandcommunicationsrequirements.Typicaloptionsincluder

25、emoteI/O,peer-to-peer,andhostcomputercommunications,aswellasLANs.Thesenetworkscanprovidereliableandcost-effectivecommunicationsbetweenasfewastwoorasmanyasseveralhundredPLCs,computers,andotherintelligentdevices.ManyPLCvendorsofferproprietarynetworkingsystemsthatareuniqueandwillnotcommunicatewithanoth

26、ermakeofPLC.Thisisbecauseofthedifferentcommunicationsprotocols,commandsequences,error-checkingschemes,andcommunicationsmediausedbyeachmanufacturer.However,itispossibletomakedifferentPLCstalktooneanother;whatsrequiredisanASCIIinterfacefortheconnection(s),alongwithconsiderableworkwithsoftware.RemoteI/

27、0systemsAremoteI/Oconfiguration,asshowninFig.4A,hastheactualinputsandoutputsatsomedistancefromthecontrollerandCPU.Thistypeofsystem,whichcanbedescribedasamaster-and-slaveconfiguration,allowsmanydistantdigitalandanalogpointstobecontrolledbyasinglePLC.Typically,remoteI/OsareconnectedtotheCPUviatwistedp

28、airorfiberopticcables.RemoteI/Oconfigurationscanbeextremelycost-effectivecontrolsolutionswhereonlyafewI/Opointsareneededinwidelyseparatedareas.Inthissituation,itsnotalwaysnecessary,orpracticalforthatmatter,tohaveacontrollerateachsite.NorisitpracticaltoindividuallyhardwireeachI/Opointoverlongdistance

29、sbacktotheCPU.Forexample,remoteI/Osystemscanbeusedinacquiringdatafromremoteplantorfacilitylocations.Informationsuchascycletimes,counts,durationorevents,etc.thencanbesentbacktothePLCformaintenanceandmanagementreporting.InaremoteI/Oconfiguration,themastercontrollerpollstheslavedI/OforitscurrentI/Ostat

30、us.TheremoteI/Osystemresponds,andthemasterPLCthensignalstheremoteI/OtochangethestateofoutputsasdictatedbythecontrolprograminthePLCsmemory.Thisentirecycleoccurshundredsoftimespersecond.Peer-to-peernetworksPeer-to-peernetworks,asshowninFig.4B,enhancereliabilitybydecentralizingthecontrolfunctionswithou

31、tsacrificingcoordinatedcontrol.Inthistypeofnetwork,numerousPLCsareconnectedtooneanotherinadaisy-chainfashion,andacommonmemorytableisduplicatedinthememoryofeach.Inthisway,whenanyPLCwritesdatatothismemoryarea,theinformationisautomaticallytransferredtoallotherPLCsinthenetwork.Theythencanusethisinformat

32、ionintheirownoperatingprograms.necessarysoftwareinterface.Theeasiestwaytoprovidesuchaninterfacetofixed-formatintelligentdevicesistouseanASCII/BASICmoduleonthePLC.ThismoduleisessentiallyasmallcomputerthatplugsintothebusofthePLC.EquippedwithRS232portsandprogrammedinBASIC,themoduleeasilycanhandleASCIIc

33、ommunicationswithperipheraldevices,dataacquisitionfunctions,programmingsequences,numbercrunching,reportanddisplaygeneration,andotherrequirements.Access,protocol,andmodulationfunctionsofLANsByusingstandardinterfacesandprotocols,LANsallowamixofdevices(PLCs,PCs,mainframecomputers,operatorinterfacetermi

34、nals,etc.)frommanydifferentvendorstocommunicatewithothersonthenetwork.Access:ALANsaccessmethodpreventstheoccurrenceofmorethanonemessageonthenetworkatatime.Therearetwocommonaccessmethods.Collisiondetectioniswherethenodeslistentothenetworkandtransmitonlyiftherearenoothermessagesonthenetwork.Iftwonodes

35、transmitsimultaneously,thecollisionisdetectedandbothnodesretransmituntiltheirmessagesgetthroughproperly.Tokenpassingallowseachnodetotransmitonlyifitsinpossessionofaspecialelectronicmessagecalledatoken.Thetokenispassedfromnodetonode,allowingeachanopportunitytotransmitwithoutinterference.Tokensusually

36、haveatimelimittopreventasinglenodefromtyingupthetokenforalongperiodoftime.Protocol:NetworkprotocolsdefinethewaymessagesarearrangedandcodedfortransmissionontheLAN.Thefollowingaretwocommontypes.Proprietaryprotocolsareuniquemessagearrangementsandcodingdevelopedbyaspecificvendorforusewiththatvendorsprod

37、uctonly.OpenprotocolsarebasedonindustrystandardssuchasTCP/IPorISO/OSImodelsandareopenlypublished.Modulation:Networkmodulationreferstothewaymessagesareencodedfortransmissionoveracable.Thetwomostcommontypesarebroadbandandbaseband.NetworktransmissioninterfacesThevastmajorityofPLCcommunicationsisdonevia

38、RS232Candtwistedpaircables.MostPLCshaveanRS232portandarecapableofhandlingcommunicationswithhostcomputers,printers,terminals,andotherdevices.Maximumtransmissionspeedis19.2Kbps.Thedistanceanddatatransmissionratesarestandardsforthevariousinterfaces.Theiractualperformanceisafunctionofthedrivingdevicesan

39、dvariessignificantlybetweenmanufacturers.Assuch,youshouldconsultthemanufacturersspecificationsforactualdistanceanddatatransmissionratecapabilities.TheonlyreallimitationonRS232Cisthe50-ftrecommendeddistancebetweendevices.WhileRS232Cinstallationsoftencanachievecablingdistancesgreaterthanthis,theunbala

40、nceddesignoftheinterfaceresultsinagreatersusceptibilitytosurroundingelectricalnoiseandreduceddataintegrity.Thisisparticularlytruewhereelectromagneticinterference(EMI)andradio-frequencyinterference(RFI)areknowntoexist.Whenlongertransmissiondistancesareneeded,RS422isabetterchoice.UnliketheRS232Cinterf

41、ace,RS422isbalanced.Eachofitsprimarysignalsconsistsoftwowiresthatarealwaysatoppositelogiclevels,withrespecttosignalground.Asaresult,theinterfacecanachievelongertransmissiondistance(4000ft)andhigherdatatransmissionrates(upto90Kbps).Inshorterruns(lessthan50ft),datatransfercanreach10Mbps.Fiberopticcomm

42、unicationsaregaininggreateracceptanceandarebeingusedinmoreandmoreinstallations.Fiberopticcableisvirtuallyimpervioustoharshenvironmentalconditionsandelectricalnoise.Also,theselinkscanspanextremelylongdistancesandtransmitdataatveryhighspeeds.Forexample,insomeLANsystems,theselinkscantransmitatrelativelyhighspeedsandspanlongdistancesbefore