可編程控制器外文翻譯文獻(xiàn)

可編程控制器外文翻譯文獻(xiàn)可編程控制器外文翻譯文獻(xiàn)(文檔含中英文對(duì)照即英文原文和中文翻譯)原文：ProgrammablelogiccontrollerPLC&\o"Input/output"input/outputarrangementsAprogrammablelogiccontroller(PLC)orprogrammablecontrollerisa\o"Digitalcomputer"digitalcomputerusedfor\o"Automation"automationof\o"Electromechanical"electromechanicalprocesses,suchascontrolofmachineryonfactory\o"Assemblyline"assemblylines,controlofamusementrides,orcontroloflightingfixtures.PLCsareusedinmanydifferentindustriesandmachinessuchaspackagingandsemiconductormachines.Unlikegeneral-purposecomputers,thePLCisdesignedformultipleinputsandoutputarrangements,extendedtemperatureranges,immunitytoelectricalnoise,andresistancetovibrationandimpact.Programstocontrolmachineoperationaretypicallystoredinbattery-backedor\o"Non-volatilestorage"non-volatilememory.APLCisanexampleofa\o"Real-timecomputing"realtimesystemsinceoutputresultsmustbeproducedinresponsetoinputconditionswithinaboundedtime,otherwiseunintendedoperationwillresult.FeaturesControlpanelwithPLC(greyelementsinthecenter).Theunitconsistsofseparateelements,fromlefttoright;\o"Powersupply"powersupply,controller,\o"Relay"relayunitsforin-andoutputThemaindifferencefromothercomputersisthatPLCsarearmoredforsevereconditions(dust,moisture,heat,cold,etc)andhavethefacilityforextensive\o"Input/output"input/output(I/O)arrangements.TheseconnectthePLCto\o"Sensor"sensorsand\o"Actuator"actuators.PLCsreadlimit\o"Switch"switches,analogprocessvariables(suchastemperatureandpressure),andthepositionsofcomplexpositioningsystems.Someevenuse\o"Machinevision"machinevision.Ontheactuatorside,PLCsoperate\o"Electricmotor"electricmotors,\o"Pneumatic"pneumaticor\o"Hydraulic"hydrauliccylinders,magnetic\o"Relay"relaysor\o"Solenoid"solenoids,oranalogoutputs.Theinput/outputarrangementsmaybebuiltintoasimplePLC,orthePLCmayhaveexternalI/OmodulesattachedtoacomputernetworkthatplugsintothePLC.Systemscale AsmallPLCwillhaveafixednumberofconnectionsbuiltinforinputsandoutputs.Typically,expansionsareavailableifthebasemodeldoesnothaveenoughI/O.ModularPLCshaveachassis(alsocalledarack)intowhichareplacedmoduleswithdifferentfunctions.TheprocessorandselectionofI/Omodulesiscustomisedfortheparticularapplication.Severalrackscanbeadministeredbyasingleprocessor,andmayhavethousandsofinputsandoutputs.AspecialhighspeedserialI/Olinkisusedsothatrackscanbedistributedawayfromtheprocessor,reducingthewiringcostsforlargeplants.UserinterfaceSeealso:\o"Listofhuman-computerinteractiontopics"Listofhuman-computerinteractiontopicsPLCsmayneedtointeractwithpeopleforthepurposeofconfiguration,alarmreportingoreverydaycontrol.A\o"Userinterface"Human-MachineInterface(HMI)isemployedforthispurpose.HMIsarealsoreferredtoasMMIs(ManMachineInterface)andGUI(GraphicalUserInterface).Asimplesystemmayusebuttonsandlightstointeractwiththeuser.Textdisplaysareavailableaswellasgraphicaltouchscreens.Morecomplexsystemsuseaprogrammingandmonitoringsoftwareinstalledonacomputer,withthePLCconnectedviaacommunicationinterface.CommunicationsPLCshavebuiltincommunicationsportsusually9-Pin\o"RS232"RS232,andoptionallyfor\o"RS485"RS485and\o"Ethernet"Ethernet.\o"Modbus"Modbusor\o"DF1(pagedoesnotexist)"DF1isusuallyincludedasoneofthe\o"Communicationsprotocols"communicationsprotocols.Others'optionsincludevarious\o"Fieldbus"fieldbusessuchas\o"DeviceNet"DeviceNetor\o"Profibus"Profibus.Othercommunicationsprotocolsthatmaybeusedarelistedinthe\o"Listofautomationprotocols"Listofautomationprotocols.MostmodernPLCscancommunicateoveranetworktosomeothersystem,suchasacomputerrunninga\o"SCADA"SCADA(SupervisoryControlAndDataAcquisition)systemorwebbrowser.PLCsusedinlargerI/Osystemsmayhavepeer-to-peer(P2P)communicationbetweenprocessors.Thisallowsseparatepartsofacomplexprocesstohaveindividualcontrolwhileallowingthesubsystemstoco-ordinateoverthecommunicationlink.Thesecommunicationlinksarealsooftenusedfor\o"Userinterface"HMI(Human-MachineInterface)devicessuchaskeypadsor\o"Personalcomputer"PC-typeworkstations.Someoftoday'sPLCscancommunicateoverawiderangeofmediaincludingRS-485,Coaxial,andeven\o"Ethernet"EthernetforI/Ocontrolatnetworkspeedsupto100Mbit/s.PLCcomparedwithothercontrolsystemsPLCsarewell-adaptedtoarangeof\o"Automation"automationtasks.Thesearetypicallyindustrialprocessesinmanufacturingwherethecostofdevelopingandmaintainingtheautomationsystemishighrelativetothetotalcostoftheautomation,andwherechangestothesystemwouldbeexpectedduringitsoperationallife.PLCscontaininputandoutputdevicescompatiblewithindustrialpilotdevicesandcontrols;littleelectricaldesignisrequired,andthedesignproblemcentersonexpressingthedesiredsequenceofoperationsin\o"Ladderlogic"ladderlogic(or\o"Functionchart(pagedoesnotexist)"functionchart)notation.PLCapplicationsaretypicallyhighlycustomizedsystemssothecostofapackagedPLCislowcomparedtothecostofaspecificcustom-builtcontrollerdesign.Ontheotherhand,inthecaseofmass-producedgoods,customizedcontrolsystemsareeconomicduetothelowercostofthecomponents,whichcanbeoptimallychoseninsteadofa"generic"solution,andwherethenon-recurringengineeringchargesarespreadoverthousandsormillionsofunits.Forhighvolumeorverysimplefixedautomationtasks,differenttechniquesareused.Forexample,aconsumer\o"Dishwasher"dishwasherwouldbecontrolledbyanelectromechanical\o"Camtimer"camtimercostingonlyafewdollarsinproductionquantities.A\o"Microcontroller"microcontroller-baseddesignwouldbeappropriatewherehundredsorthousandsofunitswillbeproducedandsothedevelopmentcost(designofpowersuppliesandinput/outputhardware)canbespreadovermanysales,andwheretheend-userwouldnotneedtoalterthecontrol.Automotiveapplicationsareanexample;millionsofunitsarebuilteachyear,andveryfewend-usersaltertheprogrammingofthesecontrollers.However,somespecialtyvehiclessuchastransitbusseseconomicallyusePLCsinsteadofcustom-designedcontrols,becausethevolumesarelowandthedevelopmentcostwouldbeuneconomic.Verycomplexprocesscontrol,suchasusedinthechemicalindustry,mayrequirealgorithmsandperformancebeyondthecapabilityofevenhigh-performancePLCs.Veryhigh-speedorprecisioncontrolsmayalsorequirecustomizedsolutions;forexample,aircraftflightcontrols.Programmablecontrollersarewidelyusedinmotioncontrol,positioningcontrolandtorquecontrol.SomemanufacturersproducemotioncontrolunitstobeintegratedwithPLCsothat\o"G-code"G-code(involvinga\o"CNC"CNCmachine)canbeusedtoinstructmachinemovements.\o""[1]PLCsmayincludelogicforsingle-variablefeedbackanalogcontrolloop,a"proportional,integral,derivative"or"\o"PIDcontroller"PIDcontroller."APIDloopcouldbeusedtocontrolthetemperatureofamanufacturingprocess,forexample.HistoricallyPLCswereusuallyconfiguredwithonlyafewanalogcontrolloops;whereprocessesrequiredhundredsorthousandsofloops,a\o"Distributedcontrolsystem"distributedcontrolsystem(DCS)wouldinsteadbeused.However,asPLCshavebecomemorepowerful,theboundarybetweenDCSandPLCapplicationshasbecomelessclear-cut.PLCshavesimilarfunctionalityas\o"RemoteTerminalUnit"RemoteTerminalUnits.AnRTU,however,usuallydoesnotsupportcontrolalgorithmsorcontrolloops.Ashardwarerapidlybecomesmorepowerfulandcheaper,\o"RemoteTerminalUnit"RTUs,PLCsand\o"DistributedControlSystem"DCSsareincreasinglybeginningtooverlapinresponsibilities,andmanyvendorssellRTUswithPLC-likefeaturesandviceversa.TheindustryhasstandardizedontheIEC61131-3functionalblocklanguageforcreatingprogramstorunonRTUsandPLCs,althoughnearlyallvendorsalsoofferproprietaryalternativesandassociateddevelopmentenvironments.DigitalandanalogsignalsDigitalordiscretesignalsbehaveasbinaryswitches,yieldingsimplyanOnorOffsignal(1or0,TrueorFalse,respectively).Pushbuttons,limitswitches,and\o"Photoelectricsensor"photoelectricsensorsareexamplesofdevicesprovidingadiscretesignal.Discretesignalsaresentusingeither\o"Voltage"voltageor\o"Current(electricity)"current,whereaspecificrangeisdesignatedasOnandanotherasOff.Forexample,aPLCmightuse24VDCI/O,withvaluesabove22VDCrepresentingOn,valuesbelow2VDCrepresentingOff,andintermediatevaluesundefined.Initially,PLCshadonlydiscreteI/O.Analogsignalsarelikevolumecontrols,witharangeofvaluesbetweenzeroandfull-scale.Thesearetypicallyinterpretedasintegervalues(counts)bythePLC,withvariousrangesofaccuracydependingonthedeviceandthenumberofbitsavailabletostorethedata.AsPLCstypicallyuse16-bitsignedbinaryprocessors,theintegervaluesarelimitedbetween-32,768and+32,767.Pressure,temperature,flow,andweightareoftenrepresentedbyanalogsignals.Analogsignalscanuse\o"Voltage"voltageor\o"Current(electricity)"currentwithamagnitudeproportionaltothevalueoftheprocesssignal.Forexample,ananalog\o"4-20mA"4-20mAor0-10

Vinputwouldbe\o"Analog-to-digitalconverter"convertedintoanintegervalueof0-32767.\o"Currentloop"Currentinputsarelesssensitivetoelectricalnoise(i.e.fromweldersorelectricmotorstarts)thanvoltageinputs.ExampleAsanexample,sayafacilityneedstostorewaterinatank.Thewaterisdrawnfromthetankbyanothersystem,asneeded,andourexamplesystemmustmanagethewaterlevelinthetank.Usingonlydigitalsignals,thePLChastwodigitalinputsfrom\o"Floatswitch"floatswitches(LowLevelandHighLevel).Whenthewaterlevelisabovetheswitchitclosesacontactandpassesasignaltoaninput.ThePLCusesadigitaloutputtoopenandclosetheinlet\o"Valve"valveintothetank.WhenthewaterleveldropsenoughsothattheLowLevelfloatswitchisoff(down),thePLCwillopenthevalvetoletmorewaterin.OncethewaterlevelraisesenoughsothattheHighLevelswitchison(up),thePLCwillshuttheinlettostopthewaterfromoverflowing.Thisrungisanexampleofsealinlogic.Theoutputissealedinuntilsomeconditionbreaksthecircuit.|||LowLevelHighLevelFillValve||[/]|[/](OUT)|||||||||||FillValve|||[]||||||Ananalogsystemmightuseawater\o"Pressuresensor"pressuresensorora\o"Loadcell"loadcell,andanadjustable(throttling)drippingoutofthetank,thevalveadjuststoslowlydripwaterbackintothetank.Inthissystem,toavoid'flutter'adjustmentsthatcanwearoutthevalve,manyPLCsincorporate"\o"Hysteresis"hysteresis"whichessentiallycreatesa"\o"Deadband"deadband"ofactivity.Atechnicianadjuststhisdeadbandsothevalvemovesonlyforasignificantchangeinrate.Thiswillinturnminimizethemotionofthevalve,andreduceitswear.Arealsystemmightcombinebothapproaches,usingfloatswitchesandsimplevalvestopreventspills,andaratesensorandratevalvetooptimizerefillratesandprevent\o"Waterhammer"waterhammer.Backupandmaintenancemethodscanmakearealsystemverycomplicated.ProgrammingPLCprogramsaretypicallywritteninaspecialapplicationonapersonalcomputer,thendownloadedbyadirect-connectioncableoroveranetworktothePLC.TheprogramisstoredinthePLCeitherinbattery-backed-up\o"RAM"RAMorsomeothernon-volatile\o"Flashmemory"flashmemory.Often,asinglePLCcanbeprogrammedtoreplacethousandsof\o"Relay"relays.Underthe\o"IEC61131-3"IEC61131-3standard,PLCscanbeprogrammedusingstandards-basedprogramminglanguages.Agraphicalprogrammingnotationcalled\o"Sequentialfunctionchart"SequentialFunctionChartsisavailableoncertainprogrammablecontrollers.Recently,theInternationalstandard\o"IEC61131-3"IEC61131-3hasbecomepopular.IEC61131-3currentlydefinesfiveprogramminglanguagesforprogrammablecontrolsystems:FBD(\o"Functionblockdiagram"Functionblockdiagram),LD(\o"Ladderlogic"Ladderdiagram),ST(\o"Structuredtext"Structuredtext,similartothe\o"Pascalprogramminglanguage"Pascalprogramminglanguage),IL(\o"Instructionlist"Instructionlist,similarto\o"Assemblylanguage"assemblylanguage)andSFC(\o"Sequentialfunctionchart"Sequentialfunctionchart).Thesetechniquesemphasizelogicalorganizationofoperations.WhilethefundamentalconceptsofPLCprogrammingarecommontoallmanufacturers,differencesinI/Oaddressing,memoryorganizationandinstructionsetsmeanthatPLCprogramsareneverperfectlyinterchangeablebetweendifferentmakers.Evenwithinthesameproductlineofasinglemanufacturer,differentmodelsmaynotbedirectlycompatible.HistoryOriginThePLCwasinventedinresponsetotheneedsoftheAmericanautomotivemanufacturingindustry.Programmablecontrollerswereinitiallyadoptedbytheautomotiveindustrywheresoftwarerevisionreplacedthere-wiringofhard-wiredcontrolpanelswhenproductionmodelschanged.BeforethePLC,control,sequencing,andsafetyinterlocklogicformanufacturingautomobileswasaccomplishedusinghundredsorthousandsof\o"Relay"relays,\o"Camtimer"camtimers,and\o"Drumsequencer(pagedoesnotexist)"drumsequencersanddedicatedclosed-loopcontrollers.Theprocessforupdatingsuchfacilitiesfortheyearlymodel\o"Changeover"change-overwasverytimeconsumingandexpensive,astherelaysystemsneededtoberewiredbyskilledelectricians.In1968GMHydramatic(theautomatictransmissiondivisionof\o"GeneralMotors"GeneralMotors)issuedarequestforproposalforanelectronicreplacementforhard-wiredrelaysystems.ThewinningproposalcamefromBedfordAssociatesof\o"Bedford,Massachusetts"Bedford,Massachusetts.ThefirstPLC,designatedthe084becauseitwasBedfordAssociates'eighty-fourthproject,wastheresult.BedfordAssociatesstartedanewcompanydedicatedtodeveloping,manufacturing,selling,andservicingthisnewproduct:Modicon,whichstoodforMOdularDIgitalCONtroller.Oneofthepeoplewhoworkedonthatprojectwas\o"DickMorley"DickMorley,whoisconsideredtobethe"father"ofthePLC.TheModiconbrandwassoldin1977to\o"GouldElectronics"GouldElectronics,andlateracquiredbyGermanCompany\o"AEG"AEGandthenbyFrench\o"SchneiderElectric"SchneiderElectric,thecurrentowner.Oneoftheveryfirst084modelsbuiltisnowondisplayatModicon'sheadquartersin\o"NorthAndover,Massachusetts"NorthAndover,Massachusetts.ItwaspresentedtoModiconby\o"GeneralMotors"GM,whentheunitwasretiredafternearlytwentyyearsofuninterruptedservice.TheautomotiveindustryisstilloneofthelargestusersofPLCs,andModiconstillnumberssomeofitscontrollermodelssuchthattheyendwitheighty-four.DevelopmentEarlyPLCsweredesignedtoreplacerelaylogicsystems.ThesePLCswereprogrammedin"\o"Ladderlogic"ladderlogic",whichstronglyresemblesaschematicdiagramofrelaylogic.ModernPLCscanbeprogrammedinavarietyofways,fromladderlogictomoretraditionalprogramminglanguagessuchasBASICandC.Anothermethodis\o"StateLogic"StateLogic,a\o"VeryHighLevelProgrammingLanguage"VeryHighLevelProgrammingLanguagedesignedtoprogramPLCsbasedon\o"Statediagram"StateTransitionDiagrams.ManyoftheearliestPLCsexpressedalldecisionmakinglogicinsimple\o"Ladderlogic"ladderlogicwhichappearedsimilartoelectricalschematicdiagrams.Theelectricianswerequiteabletotraceoutcircuitproblemswithschematicdiagramsusingladderlogic.Thisprogramnotationwaschosentoreducetrainingdemandsfortheexistingtechnicians.OtherearlyPLCsusedaformof\o"Instructionlist"instructionlistprogramming,basedonastack-basedlogicsolver.ProgrammingEarlyPLCs,uptothemid-1980s,wereprogrammedusingproprietaryprogrammingpanelsorspecial-purposeprogramming\o"Computerterminal"terminals,whichoftenhaddedicatedfunctionkeysrepresentingthevariouslogicalelementsofPLCprograms.Programswerestoredoncassettetapecartridges.Facilitiesforprintinganddocumentationwereveryminimalduetolackofmemorycapacity.TheveryoldestPLCsusednon-volatile\o"Magneticcorememory"magneticcorememory.FunctionalityThefunctionalityofthePLChasevolvedovertheyearstoincludesequentialrelaycontrol,motioncontrol,\o"Processcontrol"processcontrol,\o"Distributedcontrolsystem"distributedcontrolsystemsand\o"Computernetwork"networking.Thedatahandling,storage,processingpowerandcommunicationcapabilitiesofsomemodernPLCsareapproximatelyequivalentto\o"Desktopcomputer"desktopcomputers.PLC-likeprogrammingcombinedwithremoteI/Ohardware,allowageneral-purposedesktopcomputertooverlapsomePLCsincertainapplications.SuppliersWellknownPLCbrandsinclude\o"SiemensAG"Siemens,\o"Allen-Bradley"Allen-Bradley,\o"IDEC"IDEC,\o"ABBLtd."ABB,\o"Mitsubishi"Mitsubishi,\o"Omron"Omron,Honeywell,\o"SchneiderElectric"SchneiderElectric,Saia-BurgessControls,and\o"GEFanucAutomationNorthAmerica,Inc."GeneralElectric.

可編程控制器PLC和輸入輸出接口的排布一臺(tái)PLC或者稱為程序控制器是用于機(jī)電一體化進(jìn)程的全自動(dòng)工控機(jī)，如對(duì)機(jī)械裝配流水線、汽車駕乘、照明系統(tǒng)的控制。PLC可用于許多不同的儀器設(shè)備上，比如：包裝機(jī)械和半導(dǎo)體儀器。PLC不同于平常使用的計(jì)算機(jī)，它的開發(fā)源自于大量的輸入與輸出信號(hào)的排布，能夠在較大的溫度范圍下保持良好的工作狀態(tài)，不受電磁噪音的干擾，不受震動(dòng)和撞擊的影響。用于控制機(jī)械運(yùn)作的程序被存儲(chǔ)在使用電池的記憶體或者具有閃存作用的存儲(chǔ)器中。PLC是典型的在線系統(tǒng)，在有輸入信號(hào)之后的很短的時(shí)間內(nèi)一定會(huì)有輸出，否則會(huì)有不必要的結(jié)果產(chǎn)生。PLC的作用：基于PLC的控制面板（控制設(shè)備的核心部分是PLC）。整個(gè)面板是由幾個(gè)具有獨(dú)立功能的模塊組成，從左到右：電源，控制器，繼電器等……實(shí)現(xiàn)了輸入到輸出的功能。PLC與普通計(jì)算機(jī)之間的主要區(qū)別在于PLC能夠在任何環(huán)境下保持良好的工作狀態(tài)（包括有灰塵，潮濕，高溫，低溫等等）并且有許多閑置的接口可以用來(lái)進(jìn)行信號(hào)的輸入輸出。這些接口連接了PLC和傳感器與激勵(lì)端口。PLC能夠讀取限位開關(guān)信號(hào)；模擬工藝參數(shù)（比如溫度和壓強(qiáng)），和對(duì)整個(gè)系統(tǒng)各個(gè)部件定位。一些PLC甚至可以用于機(jī)械動(dòng)作的模擬。作為激勵(lì)端，PLC控制了電機(jī)，汽缸或是液壓缸，電磁繼電器，螺線管，或者可以模擬輸出。一系列的輸入輸出端口可以集成在一臺(tái)PLC上，PLC也可以通過(guò)特定的模塊來(lái)連接控制端的微機(jī)。系統(tǒng)的數(shù)量范圍一臺(tái)小型PLC有一定數(shù)量的輸入輸出端口。作為PLC的一大特點(diǎn)，當(dāng)主機(jī)輸入輸出接口數(shù)量不夠的時(shí)候，可以外接擴(kuò)展端口。PLC的擴(kuò)展模塊都帶有一種底盤（也可稱為支架），根據(jù)不同的用途將模塊放入不同的位置。不同模塊的處理器和選擇器的輸入輸出接口可根據(jù)特定的用途來(lái)選擇。一些個(gè)別的模塊可以有一臺(tái)獨(dú)立的處理器來(lái)直接驅(qū)動(dòng)，并且可以容納大量的輸入輸出信號(hào)。為了降低大型工廠的配線成本，一種特制的高速I/O接口被廣泛應(yīng)用以使那些獨(dú)立的模塊可以與主處理器分放在不同的位置。用戶界面：PLC需要在外觀結(jié)構(gòu)，報(bào)警記錄，以及日常的控制上適應(yīng)操作者。人機(jī)界面（HMI）實(shí)現(xiàn)了這樣的目的，HMI與MMI和GUI屬于同一類型的操作界面。為了適應(yīng)操作者，一個(gè)簡(jiǎn)單的系統(tǒng)需要具備按鈕和顯示。顯示的程序可在觸摸屏上直接調(diào)試。許多復(fù)雜的編譯程序和監(jiān)控軟件都安裝在計(jì)算機(jī)上，該計(jì)算機(jī)與PLC通過(guò)數(shù)據(jù)接口連接。通信方式PLC的通信接口一般采用9針的RS232接口，并且兼容RS485和以太網(wǎng)絡(luò)接口。常用的通信協(xié)議包含了Modbus或者DF1。其他可供選擇的也包括了不同的fieldbuses，例如devicenet或者profibus。同時(shí)自動(dòng)通信協(xié)議已經(jīng)包含了其他的通信協(xié)議。大多數(shù)最新的PLC已經(jīng)可以通過(guò)網(wǎng)絡(luò)與另一臺(tái)PLC的系統(tǒng)通信，正如一臺(tái)電腦運(yùn)行SCADA（數(shù)據(jù)采集與監(jiān)視控制系統(tǒng)）或者運(yùn)行一個(gè)網(wǎng)頁(yè)瀏覽器。在大流量輸入輸出系統(tǒng)中，兩臺(tái)PLC之間的通信采用了P2P（對(duì)等聯(lián)網(wǎng)）技術(shù)。這讓獨(dú)立的幾個(gè)復(fù)雜進(jìn)程能夠在當(dāng)子系統(tǒng)在相互通信的時(shí)候被單獨(dú)控制。這種通信方式也常使用于人機(jī)交互界面，比如鍵盤或者計(jì)算機(jī)工作站。當(dāng)今世界上已經(jīng)有部分的PLC支持更廣泛的信號(hào)傳輸方式，包括RS-485接口，同步傳輸，甚至可以當(dāng)網(wǎng)絡(luò)傳輸速度達(dá)到100Mbit/s時(shí)利用以太網(wǎng)直接使用計(jì)算機(jī)控制.PLC與其他控制系統(tǒng)的比較PLC能夠很好的適應(yīng)大部分自動(dòng)化控制任務(wù)。在傳統(tǒng)工藝流水線上，開發(fā)以及維護(hù)全自動(dòng)系統(tǒng)的成本要高于整個(gè)PLC控制系統(tǒng)，同時(shí)，現(xiàn)代工業(yè)正期待這樣的轉(zhuǎn)變。PLC自帶的輸入輸出設(shè)備使得工業(yè)控制器和設(shè)備得到了很好的協(xié)調(diào)；微電子技術(shù)在現(xiàn)代工業(yè)被廣泛的需求，設(shè)計(jì)中心采用了梯形圖（或者功能表圖）的程序編譯方法。PLC的控制界面非常友好，整臺(tái)PLC設(shè)備的成本比同級(jí)的特制控制器低出不少。從另一方面看，由于大批量生產(chǎn)，定制控件系統(tǒng)的開發(fā)源于生產(chǎn)成本的控制，定制控件系統(tǒng)將取代“一般的”解決方案，在這個(gè)系統(tǒng)中，大量一次性電器電源被集成在一起不同的技術(shù)用于大信息容量或者簡(jiǎn)單的自動(dòng)控制系統(tǒng)中。例如：一臺(tái)家用洗碗機(jī)所使用的機(jī)電一體化時(shí)序控制器的成本僅為幾美元。一臺(tái)基于微型控制器的設(shè)計(jì)將會(huì)因?yàn)槭褂糜猛緩V泛使得整個(gè)工程的開發(fā)經(jīng)費(fèi)（電源的設(shè)計(jì)以及輸入輸出設(shè)備的成本）分?jǐn)偟礁鱾€(gè)商業(yè)領(lǐng)域，并且終端用戶無(wú)需修改其中的控制程序。自動(dòng)分類系統(tǒng)便是一個(gè)典型的例子；每年有大量的產(chǎn)品，僅僅有極少數(shù)的客戶需要自主修改一些控制程序。然而，一些特制的汽車（運(yùn)輸巴士）從經(jīng)濟(jì)的角度上出發(fā)使用PLC而不是定制控件系統(tǒng)，因?yàn)橛休^低的信息存儲(chǔ)量和并不低廉的開發(fā)成本。非常復(fù)雜的程序控制，一般用于化工業(yè)，需要一系列的運(yùn)算法則，即使是高性能的PLC也是很難達(dá)到的。極高的運(yùn)算速度和運(yùn)算精度可能需要特殊的解決方案；例如宇宙飛船的飛行控制。程序控制器常常在運(yùn)動(dòng)控制系統(tǒng)中被廣泛應(yīng)用，定位控制和控制扭矩。一些制造商把運(yùn)動(dòng)控制單元與PLC結(jié)合生成G代碼（在數(shù)控機(jī)床中被運(yùn)用）以用于對(duì)機(jī)械運(yùn)動(dòng)的控制。正如操作臺(tái)一樣，PLC的邏輯系統(tǒng)為帶有反饋的循環(huán)控制系統(tǒng)，一種“比例，積分，微分控制”或者是“PID控制”，例如一個(gè)PID循環(huán)可用于對(duì)制造過(guò)程中的溫度控制。傳統(tǒng)的PLC常常僅配置了簡(jiǎn)單的操作系統(tǒng)。處理器需要成百上千的循環(huán)，所以一種分布式控制系統(tǒng)（DCS）將取而代之。然而，即使PLC的功能已經(jīng)如此強(qiáng)大，有關(guān)與PLC以及DCS系統(tǒng)的相關(guān)軟件少之又少。PLC在使用的廣泛性上與遠(yuǎn)程終端設(shè)備（RTU）有著相似之處。然而RTU并不支持函數(shù)計(jì)算和反饋系統(tǒng)。由于硬件變得更加強(qiáng)大而且廉價(jià)，RTU,PLC,以及DCS的發(fā)展在功能上已經(jīng)相互補(bǔ)足了，許多廠商將RTU設(shè)備嵌入PLC界面中，同樣反之亦然。工業(yè)上已經(jīng)對(duì)IEC61131-3的功能模塊的編譯語(yǔ)言進(jìn)行了規(guī)范化以便于在RTU和PLC上使用，盡管生產(chǎn)廠商已經(jīng)向客戶提供了編譯軟件。數(shù)字與模擬信號(hào)數(shù)字信號(hào)（離散信號(hào)）一般為二進(jìn)制轉(zhuǎn)換，僅受開關(guān)信號(hào)（1或者0；正確或錯(cuò)誤；識(shí)別）的影響。按鈕，限位開關(guān)，光電傳感器都是輸出離散信號(hào)的典型元器件。離散信號(hào)通過(guò)電壓或者電流傳輸，當(dāng)電壓或者電流在指定范圍內(nèi)接通反之或者斷開。例如，一臺(tái)使用24v直流電源的PLC的輸入輸出接口，當(dāng)電壓大于22V的時(shí)候接口接通，當(dāng)直流電壓低于2V的時(shí)候接口斷開，2V~22V中的電壓并不確定接通或斷開。最初的PLC只有離散型接口（數(shù)字接口）。模擬信號(hào)的控制與音量的控制類似，有一個(gè)大小的零位和上限，在PLC上被認(rèn)為是計(jì)數(shù)器，依靠驅(qū)動(dòng)器具有廣泛的調(diào)整空間和精度并且一系列的數(shù)據(jù)可以被存儲(chǔ)下來(lái)。典型的PLC使用16進(jìn)制處理器，信號(hào)數(shù)值的范圍在-32768至+32767之間。壓強(qiáng)，溫度，流量，以及重量可以被轉(zhuǎn)化為模擬信號(hào)。通過(guò)電流或電壓可以按比例放大或縮小模擬信號(hào)。例如：一個(gè)4~20毫安或者0~10伏的輸入模擬信號(hào)可通過(guò)轉(zhuǎn)換獲得的值可任意在0~32767范圍之間。電流輸入信號(hào)的抗電磁干擾能力要強(qiáng)于電壓輸入信號(hào)。范例舉個(gè)例子，假定某個(gè)設(shè)備需要將水存儲(chǔ)在水槽中。水槽的水能夠在需要的時(shí)候被某個(gè)系統(tǒng)抽出，我們的范例系統(tǒng)需要能夠控制槽中水位。僅僅使用數(shù)字信號(hào)，PLC的兩種輸入信號(hào)來(lái)浮球開關(guān)（高電平和低電平），當(dāng)水位高于限位開關(guān)時(shí)，開關(guān)自動(dòng)切斷進(jìn)水信號(hào)。PLC利用數(shù)字脈沖輸出控制水槽的進(jìn)出閥門。當(dāng)水位足夠低