1PLCelementaryknowledgesynopsisIntheautomatedcontroldomain,PLCisonekindofimportantcontroldevice.Atpresent,intheworldhasmorethan200factoriestoproducemorethan300varietiesPLCproduct,appliesintheautomobile(23%),thegrainprocessing(16.4%),chemistry/drugsmanufacture(14.6%),themetal/mine(11.5%),thepaperpulp/papermaking(11.3%)andsoontheprofession.InordertomakefellowbeginnersconvenientlytounderstandPLC,thisarticletothePLCdevelopment,thebasicstructure,thedisposition,usingandsoontheelementaryknowledgemakesasynopsis.First,PLCdevelopmentcourseIntheindustrialproductionprocess,themassiveswitchesquantitysequentialcontrol,itcarriesonthesmoothmovementaccordingtothelogicalcondition,anddeferstothelogicalrelationstocarryonthechain-likeprotectionmovementthecontrol,andmassivedataacquisition.Inthetradition,thesefunctionsarerealizethroughairoperatedortheelectricitycontrolsystem.In1968AmericanGM(generalautomobile)thecompanyproposedthesubstitutioncontinuestheelectricitycontroldevicetherequest,thesecondyear,theAmericannumeralcompanydevelopedbasedontheintegratedcircuitandtheelectronictechnologycontroldevice,usedsequencedthemethodtoapplyforthefirsttimetotheelectricalcontrol,thiswasthefirstgenerationofprogrammableforewordcontroller,calledProgrammableController(PC).Afterthepersonalcomputer(iscalledPC)todevelop,inordertobeconvenient,alsoinordertoreflecttheprogrammablecontrollerthefunctioncharacteristic,theprogrammableforewordcontrollerchoosesanameisProgrammableLogicController(PLC),now,stillfrequentlywascalledPLCPC.ThePLCdefinitionhasmanykinds.Theinternationalelectriciancommittee(IEC)toPLCthedefinitionis:Theprogrammablecontrollerisonekindofdigitaloperationoperationelectronicsystem,speciallyforappliesundertheindustryenvironmentdesigns.Itusestheprogrammableforewordthememory,usesfortocarryoutthelogicoperation,thesequentialcontrolinitsinternalstorage,fixedtime,countswithoperationtheandsoonarithmeticoperationinstruction,andthroughdigital,thesimulationinputandtheoutput,controlseachkindoftypethemachineryortheproductionprocess.Theprogrammableforewordcontrolleranditstherelatedequipment,allshouldaccordingtoeasyformawholewiththeindustrycontrolsystem,2iseasytoexpanditsfunctiontheprincipledesign.Onthecentury80stothe90sintermediatestages,arePLCdevelopthequickesttime,theyearlyratecontinuouslymaintenanceare30-40%.Inthistime,PLCintheprocessingsimulationquantityability,thedigitaloperationability,theman-machineconnectionabilityandthenetworkingcapabilityobtainsthelargescaleenhancement,PLCgraduallyenterstheprocesscontroldomain,substitutedincertainapplicationshasbeenatthedominantpositionintheprocesscontroldomaintheDCSsystem.PLChastheversatilitystrongly,theeasytooperate,theadaptionsurfacebroad,thereliabilityhigh,theantijammingabilitystrong,theprogrammingissimpleandsoonthecharacteristic.PLCintheindustrialautomationcontrolspeciallyisinthesequentialcontrolstatus,infuturewhichmayforesee,isunabletosubstitute.Second,PLCconstitutionFromthestructuretheminute,PLCdividesintothestationarytypeandthecombinedtype(moduletype)twokinds.StationaryPLCincludingtheCPUboard,theI/Oboard,demonstratedthekneadingboard,thememoryblock,thepowersourceandsoon,theseelementgroupssynthesizeanotdismantablewhole.ModuletypePLCincludingtheCPUmodule,theI/Omodule,thememory,thepowersourcemodule,theledgerwallortherack,thesemodulesmaydefertothecertainrulecombinationdisposition.Second,PLCconstitution.Third,CPUconstitutionCPUisthePLCcore,playsnervecentersrole,everytimewrapsPLCatleasttohaveCPU,itfunctionreceiveandstorageuserprogramanddatawhichentrustswithaccordingtothePLCsystemprogram,withscanningwaygatheringtheconditionorthedatawhichsendsbythesceneinputdevice,andstoresthestipulationintheregister,simultaneously,diagnosesthepowersourceandinthePLCinternalcircuitactivestatusandtheprogrammingprocessgrammaticalerrorandsoon.Afterentersthemovement,readsfromtheuserprogrammemorybythestriptakestheinstruction,thedutywhichstipulatedaccordingtotheinstructionproducesthecorrespondingcontrolsignalagainaftertheanalysis,directstherelatedcontrolcircuit.CPUmainlybythelogicunit,thecontroller,theregisterandrealizesthedata,thecontrolandtheconditionmainlineconstitutionwhichbetweenthemrelates,theCPUunitalsoincludestheperipherychip,themainlineconnectionandtherelatedelectriccircuit.Thememorymainlyusesinthestoredroutineandthedata,isthePLCessentialcompositionunit.Lookedlikeintheuser,nonessentialmultianalysisCPUinternalcircuit,butor3shouldhavetheenoughunderstandingtoeachpartofworkmechanism.TheCPUcontrollercontrolstheCPUwork,readsbyittakestheinstruction,theinterpretiveorderandcarriesouttheinstruction.Buttheworkrhythmbyshakesthesignalcontrol.Thelogicunitusesintocarryonthenumeralorthelogicoperation,worksunderthecontrollerdirection.Theregisterparticipationoperation,coexistsstorestheoperationtheintermediateresult,italsoisworksunderthecontrollerdirection.TheCPUspeedandthememorycapacityarethePLCimportantparameter,theyaredecidingthePLCworkingspeed,theIOquantityandthesoftwarecapacityandsoon,thereforeislimitingthecontrolscale.Fourth,I/OmodulePLCandtheelectricalreturnrouteconnection,is(I/O)completesthroughtheinputoutputunit.TheI/OmoduleintegratedthePLCI/Oelectriccircuit,itsinputtemporarystoragedevicereflectioninputsignalcondition,outputpointreflectionoutputlatchcondition.TheloadmoduletransformstheelectricalsignalthedigitalsignaltoenterthePLCsystem,theoutputmoduleisopposite.I/Odividesintotheswitchquantityinput(DI),switchquantityoutput(DO),simulationquantityinput(AI),simulationquantityoutput(AO)andsoonmodule.Theswitchquantityisrefershasandcloses(or1and0)twokindofconditionssignals,thesimulationquantityisonlyaquantitywhichreferscontinuouslychanges.CommonlyusedI/Oclassifiesasfollows:Switchquantity:Dividesequallyaccordingtothevoltagewater,has220VAC,110VAC,24VDC,dividesaccordingtotheisolationway,hastherelayisolationandthetransistorisolation.Simulationquantity:Dividesaccordingtothesignaltype,hastheelectriccurrent(4-20mA,0-20mA),thevoltage(0-10V,0-5V,-10-10V)andsoon,dividesaccordingtotheprecision,has12bit,14bit,16bitandsoon.BesidesabovegeneralI/O,butalsohasthespecialI/Omodule,likemoduleandsoonthermalresistance,thermo-element,pulse.AccordingtotheI/Opointsdeterminationmodulespecificationandthequantity,theI/Omodulemaybemanymaybefew,butitsbiggestnumberthebasicdispositionabilitywhichcanmanageCPU,namelybiggestledgerwallorrackKeyslotnumberlimit.Fifth,powersourcemoduleThePLCpowersourceusesinisthePLCvariousmodulesintegratedcircuitprovidestheworkpowersource.Atthesametime,somealsoprovides24Vforthe4inputcircuittheworkpowersource.Themainsinputtypeincludes:(Whatthealternatingcurrentsupply(220VACor110VAC),thedirect-currentpowersupplyiscommonlyusedis24VAC).Sixth,ledgerwallorrackThemajoritymoduletypePLCuseledgerwallortherack,itsfunctionis:Ontheelectricity,realizesduringvariousmodulesrelation,enablesCPUtovisitontheledgerwallallmodules,onthemachinery,realizesduringvariousmodulesconnection,enablevariousmodulestoconstituteawhole.Seventh,PLCsystemotherequipment1st,programstheequipment:TheprogrammingisthePLCdevelopmentapplication,themonitormovement,theinspectionmaintainstheessentialcomponent,usesintoprogram,makessomehypothesestothesystem,monitorsthesystemworkingconditionwhichPLCandPLCcontrols,butitnotdirectlyparticipatesinthescenecontrolmovement.SmallprogrammingPLCgenerallyhasthegraspingprogramming,atpresentgenerally(movementprogrammingsoftware)actsastheprogrammingbythecomputer.2nd,man-machinecontactsurface:Thesimplestman-machinecontactsurfaceistheindicatinglampandthebutton,atpresenttheliquidcrystalscreen(ortouchesscreen)aformulawritingstyleoperatorterminalapplicationtobemoreandmorewidespread,(movementconfigurationsoftware)actsastheman-mach