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ProgrammableLogicControllers(PLC),acomputingdeviceinventedbyRichardE.Morleyin1968,havebeenwidelyusedinindustryincludingmanufacturingsystems,transportationsystems,chemicalprocessfacilities,andmanyothers.Atthattime,thePLCplacedthehardwiredlogicwithsoft-wiredlogicorso-calledrelayladderlogic(RLL),aprogramminglanguagevisuallyresemblingthehardwiredlogic,andreducedtherebytheconfigurationtimefrom6monthsdownto6days[MoodyandMorley,1999].AlthoughPCbasedcontrolhasstartedtocomeintoplace,PLCbasedcontrolwillremainthetechniquetowhichthemajorityofindustrialapplicationswilladhereduetoitshigherperformance,lowerprice,andsuperiorreliabilityinharshenvironments.Moreover,accordingtoastudyonthePLCmarketofFrostandSullivan[1995],anincreaseoftheannualsalesvolumeto15millionPLCsperyearwiththehardwarevalueofmorethan8billionUSdollarshasbeenpredicted,thoughthepricesofcomputinghardwareissteadilydropping.TheinventorofthePLC,RichardEMorley,fairlyconsidersthePLCmarketasa5-billionindustryatthepresenttime.
KeyWords:
PLC,performance,market
1Introduction
Alongwiththedevelopmentoftheages,thetechniquethatisnowadaysisalsograduallyperfect,thecompetitionplaysmoremorestrong;
theoperationthatlistdependstheartificialhasalreadycan'
tsatisfiedwiththecurrentmanufacturingindustryforeground,alsocan'
tguaranteetherequestofthehigherquantityandhighnewtheimageofthetechniquebusinessenterprise.
Thepeopleseeinproducepractice,automatebroughtthetremendousconvenienceandtheproductquantitiesforpeopleupofassurance,alsoeasedthepersonnel'
slaborstrength,reducetheestablishmentonthepersonnel.Thetargetcontrolofthehardrealizationinmanycomplicatedproductionlines,wholeandexcellentturn,thebestdecisionetc.,well-trainedoperationwork,technicalpersonnelorexpert,governorbutcanjudgeandoperateeasily,canacquirethesatisfiedresult.Theresearchtargetoftheartificialintelligencemakesuseofthecalculatorexactlytocarryout,imitatetheseintelligencesbehavior,moderatingtheworkthroughperson'
sbrainandcalculators,withthemodethatperson'
smachinecombine,forresolvetheverycomplicatedproblemtolookforthebestpath
Wecomeinsightofthecontrolthatlinksaftertheelectricappliancesinvarioussituation,thatisalreadythethattimegenerationpast,nowofafteruseinthemoldaperhapssimpleequipmentsofgrass-rootscontrolthattheelectricappliancescandoforthelowlevelonly;
AndthePLCemergencealsobecametheepoch-makingtopic,addingthevividsoftwarecontrolthroughaveryandstablehardware,makingtheautomationheadforthenewhightide.
2PLCcharacteristicsandcontainment
2.1ThePLCbiggestcharacteristics
ThePLCbiggestcharacteristicsliein:
Theelectricalengineeringteacheralreadynolongerelectrichardwareuptoomanycalculationsesofcost,aslongasordertheimportationthatthebuttonswitchortheimportationofthesensorsordertolinkthePLCupcansolveproblem,passtooutputtoordertheconjunctioncontactmachineorcontrolthestartequipmentsofthebigpoweraftertheelectricappliances,buttheexportationequipmentsdirectconjunctionofthesmallpowercan.
Figure1.OpenframePLC
2.2PLCinternalcontainment
PLCinternalcontainmenthaveCPU,andtaketohaveanI/Oforexpandofexteriortoconnectapeople'
saddressandsavingmachinethreebigpiecestoconstitute,CPUcoreisfromanormanyistiredtoaddthemachinetoconstitute,mathematicsthattheyhavethelogicoperationability,andcanreadtheproceduresavethecontentsofthemachinetodrivethehomologoussavingmachineandI/Ostoconnectafterpassthecalculation;
TheI/Oaddinnerpartistiredtheinputandoutputsystemofthemachineandexteriorlink,anddeposittherelateddataintotheproceduresavingmachineordatasavingmachine;
ThesavingmachinecandepositthedatathattheI/Oinputinthesavingmachine,andinworkadjustingtobecometiredtoaddthemachineandI/Ostoconnect,savingmachineseparatelysavingmachineRAMoftheproceduresavingmachineROManddatas,theROMcancandodepositofthedatapermanenceinthesavingmachine,butRAMonlyfortheCPUcomputesthetemporarycalculationusageofhourofbufferspace.
Figure2.PLCinputandoutputcircuits
2.3PLCadvantage
ThePLCanti-interferenceisveryandexcellent,ourrootneednotconcernitsservicelifeandtheworksituationbad,theseallproblemshavealreadynolongerbecomethetopicthatwefail,butstaytoourisaconcerntocometointernalresourcesofmakeuseofthePLCtostrengthenthecontrolabilityoftheequipmentsforus,makeourequipmentsmoregentle.
PLClanguageisnotweimagineofeditcollectedmaterialsthelanguageorlanguageofCstocarryonweavingthedistance,butthetrapezoiddiagramthattheadoptionisoriginalaftertheelectricappliancestocontrol,maketheelectricalengineeringteacherwhileweavingtowritetheprocedureveryeasycomprehendedthePLClanguage,andalotofnon-electricityprofessionalalsoveryquicklyknowandgodeepintotothePLC.
3HMI
IsPLConeoftheadvantageaboveandonly,thisisalsoonepartthatthepeoplecomprehendmoreandeasily,inalotofequipmentses,thepeoplehavealreadynolongerhopedtoseetoomanycontrolbuttons,theydamagenotonlyandeasilyandproducetheartificialerroreasiest,smallisnotamainerrorperhapsyoucanstillaccept;
Butleadevenisafatalerrorgreatlyiswhatwecan'
tistolerantof.Newtechniquealwaysforbringingmoresafeandconvenientoperationforus,makewealotofproblemsforfaceonsweepbutlight,doyouunderstandtheHMI?
SaystheHMIhereyoubasicallynotclearwhatitis,alsohavenointerestunderstanding,changeoneinsidetextexplainsitintothetouchtoholdorman-machineinterfaceyouknew,itcombineswiththePLCtoourlargerspace.
HMIthecontrolnotonlyonlyisreducedthecontrolpressbutton,increasethevividofthecontrol,moremainofitiscansequenceof,andatcanthechangedatainputtooutputthefeedbackwithdata,controlinthetemperaturecurveofimitatebutalsocankeepthemanifestationofviewtocomeout.Andcanwritethefunctionhelpprocedurethroughaplaittoprovidethehelpofvariouswhatliesinone'
spower,theonewhomakeoperatereducestheotioseerror.CurrentlytheHMIfactoryisalsomoreandmore,thefunctionisalsomoreandmorestrong,thepriceisalsomoreandmorelow,thenoodlesoftheusagearewidemoreandmore.TheHMIforegroundcansaythatthink°
tobegoodvery.
4PLCcorrespondenceanddatatransmission
Atalotofsituations,thelistisisasmoothmovementthatcan'
tguaranteetheequipmentsbythecontrolofthesinglemachine,butpasstheinformationexchangesoftheequipmentsandequipmentstoattaintheresultthatwewant.Forexampleforepackandtheexaminationoftheempressworkpreface,wewillarrivewrappinginformationfeedbacktoexaminetheplace,andexaminetheinformationoftheplacetoalsowantthefeedbacktopacking.Passtheinformationsharethustomakeboththechainconnect,becomingatotalbody,thematchofyourthatthusmakeismoreclose,ateachotherattaintoreflecttheresultthatmutuallyflick.
ThePLCcorrespondencehasalreadycomemoremorebodynowitsvalue,atthePLCandcorrespondencebetweenPLCs,canpassthecommunicationoftheinformationandtheshareofthedatastoguaranteethatoftheequipmentsmoderatesmutually,theresultthatarrivealreadytorepairwitheachother.DataconversiontheadoptionRS232betweenPLCconnecttocometothetransmissiondata,buttheRS232pickupapeopleandcanguarantee10metersonlyofdeliverthedistance,ifinthedistanceof1000meterswecanpasstheRS485tocarryonthecorrespondence,thelongerdistancecanpasstheMODELonlytocarryondeliver.
ThePLCdatatransmissionisjusttobecalledaformtoitinapieceofandcontinuousaddressthatthedataoftheinnerpartdeliverstheotherparty,we,thePLCoftheotherpartypassestoreaddatainthewatchtocarryontheoperation.Ifthedatathatdatainthewatchisatoestablishgenerally,thatisjustthegeneraldatatransmission,forexampletodayofoilpricerise,Iwanttodeliverthepriceoftheoilpricetolosetheoilallyonboard,thatistheshareofthedata;
ButtakedatainthewatchforaninstructionprocedurethatcontrolsthePLC,thathadthedifficultyverymuch,forexampleyouhavetocontrolonepedestalrobottopresstheactionworkthatyouimagine,youwilldrawupforittheformthataprocedurecombinewiththedatasendsouttopassby.
Figure3.PLCconnectionwithexperimentsboard.
4.1Formofinformationtransmission
4.1.1SimplexandDuplex
TheformthatinformationtransportcontainSimplex,theHalfduplexandtheFullduplex.ThemeaningoftheSimplexalsoistosayboth,acansendoutonly,butacanreceiveonly,forexampleaspyhecanreceivethedesignationofthesuperioronly,butcan'
tgivethesuperiorreply;
Halfduplexisalso2andcancansendoutsimilartoacceptthedata,butcan'
tsendoutandacceptatthesametime,forexamplewhenyoumakeaphonecallistocan'
tanswerthephone,theotherpartyalso;
ButtheHalfduplexisbothcansendoutandacceptthedata,andcansendoutandacceptatthesametime.BeliketheInternetisatypicalexample.
4.1.2Syn