自動化英文文獻翻譯

附錄ProgrammablelogiccontrollerFromWikipedia,thefreeencyclopediaJumpto:navigation,searchPLC&input/outputarrangementsAprogrammablelogiccontroller(PLC)orprogrammablecontrollerisadigitalcomputerusedforautomationofelectromechanicalprocesses,suchascontrolofmachineryonfactoryassemblylines,controlofamusementrides,orcontroloflightingfixtures.PLCsareusedinmanydifferentindustriesandmachinessuchaspackagingandsemiconductormachines.Unlikegeneral-purposecomputers,thePLCisdesignedformultipleinputsandoutputarrangements,extendedtemperatureranges,immunitytoelectricalnoise,andresistancetovibrationandimpact.Programstocontrolmachineoperationaretypicallystoredinbattery-backedornon-volatilememory.APLCisanexampleofarealtimesystemsinceoutputresultsmustbeproducedinresponsetoinputconditionswithinaboundedtime,otherwiseunintendedoperationwillresult.FeaturesControlpanelwithPLC(greyelementsinthecenter).Theunitconsistsofseparateelements,fromlefttoright;powersupply,controller,relayunitsforin-andoutputThemaindifferencefromothercomputersisthatPLCsarearmoredforsevereconditions(dust,moisture,heat,cold,etc)andhavethefacilityforextensiveinput/output(I/O)arrangements.TheseconnectthePLCtosensorsandactuators.PLCsreadlimitswitches,analogprocessvariables(suchastemperatureandpressure),andthepositionsofcomplexpositioningsystems.Someevenusemachinevision.Ontheactuatorside,PLCsoperateelectricmotors,pneumaticorhydrauliccylinders,magneticrelaysorsolenoids,oranalogoutputs.Theinput/outputarrangementsmaybebuiltintoasimplePLC,orthePLCmayhaveexternalI/OmodulesattachedtoacomputernetworkthatplugsintothePLC.Systemscale AsmallPLCwillhaveafixednumberofconnectionsbuiltinforinputsandoutputs.Typically,expansionsareavailableifthebasemodeldoesnothaveenoughI/O.ModularPLCshaveachassis(alsocalledarack)intowhichareplacedmoduleswithdifferentfunctions.TheprocessorandselectionofI/Omodulesiscustomisedfortheparticularapplication.Severalrackscanbeadministeredbyasingleprocessor,andmayhavethousandsofinputsandoutputs.AspecialhighspeedserialI/Olinkisusedsothatrackscanbedistributedawayfromtheprocessor,reducingthewiringcostsforlargeplants.UserinterfaceSeealso:Listofhuman-computerinteractiontopicsPLCsmayneedtointeractwithpeopleforthepurposeofconfiguration,alarmreportingoreverydaycontrol.AHuman-MachineInterface(HMI)isemployedforthispurpose.HMIsarealsoreferredtoasMMIs(ManMachineInterface)andGUI(GraphicalUserInterface).Asimplesystemmayusebuttonsandlightstointeractwiththeuser.Textdisplaysareavailableaswellasgraphicaltouchscreens.Morecomplexsystemsuseaprogrammingandmonitoringsoftwareinstalledonacomputer,withthePLCconnectedviaacommunicationinterface.CommunicationsPLCshavebuiltincommunicationsportsusually9-PinRS232,andoptionallyforRS485andEthernet.ModbusorDF1isusuallyincludedasoneofthecommunicationsprotocols.Others'optionsincludevariousfieldbusessuchasDeviceNetorProfibus.OthercommunicationsprotocolsthatmaybeusedarelistedintheListofautomationprotocols.MostmodernPLCscancommunicateoveranetworktosomeothersystem,suchasacomputerrunningaSCADA(SupervisoryControlAndDataAcquisition)systemorwebbrowser.PLCsusedinlargerI/Osystemsmayhavepeer-to-peer(P2P)communicationbetweenprocessors.Thisallowsseparatepartsofacomplexprocesstohaveindividualcontrolwhileallowingthesubsystemstoco-ordinateoverthecommunicationlink.ThesecommunicationlinksarealsooftenusedforHMI(Human-MachineInterface)devicessuchaskeypadsorPC-typeworkstations.Someoftoday'sPLCscancommunicateoverawiderangeofmediaincludingRS-485,Coaxial,andevenEthernetforI/Ocontrolatnetworkspeedsupto100Mbit/s.PLCcomparedwithothercontrolsystemsPLCsarewell-adaptedtoarangeofautomationtasks.Thesearetypicallyindustrialprocessesinmanufacturingwherethecostofdevelopingandmaintainingtheautomationsystemishighrelativetothetotalcostoftheautomation,andwherechangestothesystemwouldbeexpectedduringitsoperationallife.PLCscontaininputandoutputdevicescompatiblewithindustrialpilotdevicesandcontrols;littleelectricaldesignisrequired,andthedesignproblemcentersonexpressingthedesiredsequenceofoperationsinladderlogic(orfunctionchart)notation.PLCapplicationsaretypicallyhighlycustomizedsystemssothecostofapackagedPLCislowcomparedtothecostofaspecificcustom-builtcontrollerdesign.Ontheotherhand,inthecaseofmass-producedgoods,customizedcontrolsystemsareeconomicduetothelowercostofthecomponents,whichcanbeoptimallychoseninsteadofa"generic"solution,andwherethenon-recurringengineeringchargesarespreadoverthousandsormillionsofunits.Forhighvolumeorverysimplefixedautomationtasks,differenttechniquesareused.Forexample,aconsumerdishwasherwouldbecontrolledbyanelectromechanicalcamtimercostingonlyafewdollarsinproductionquantities.Amicrocontroller-baseddesignwouldbeappropriatewherehundredsorthousandsofunitswillbeproducedandsothedevelopmentcost(designofpowersuppliesandinput/outputhardware)canbespreadovermanysales,andwheretheend-userwouldnotneedtoalterthecontrol.Automotiveapplicationsareanexample;millionsofunitsarebuilteachyear,andveryfewend-usersaltertheprogrammingofthesecontrollers.However,somespecialtyvehiclessuchastransitbusseseconomicallyusePLCsinsteadofcustom-designedcontrols,becausethevolumesarelowandthedevelopmentcostwouldbeuneconomic.Verycomplexprocesscontrol,suchasusedinthechemicalindustry,mayrequirealgorithmsandperformancebeyondthecapabilityofevenhigh-performancePLCs.Veryhigh-speedorprecisioncontrolsmayalsorequirecustomizedsolutions;forexample,aircraftflightcontrols.Programmablecontrollersarewidelyusedinmotioncontrol,positioningcontrolandtorquecontrol.SomemanufacturersproducemotioncontrolunitstobeintegratedwithPLCsothatG-code(involvingaCNCmachine)canbeusedtoinstructmachinemovements.[1]PLCsmayincludelogicforsingle-variablefeedbackanalogcontrolloop,a"proportional,integral,derivative"or"PIDcontroller."APIDloopcouldbeusedtocontrolthetemperatureofamanufacturingprocess,forexample.HistoricallyPLCswereusuallyconfiguredwithonlyafewanalogcontrolloops;whereprocessesrequiredhundredsorthousandsofloops,adistributedcontrolsystem(DCS)wouldinsteadbeused.However,asPLCshavebecomemorepowerful,theboundarybetweenDCSandPLCapplicationshasbecomelessclear-cut.PLCshavesimilarfunctionalityasRemoteTerminalUnits.AnRTU,however,usuallydoesnotsupportcontrolalgorithmsorcontrolloops.Ashardwarerapidlybecomesmorepowerfulandcheaper,RTUs,PLCsandDCSsareincreasinglybeginningtooverlapinresponsibilities,andmanyvendorssellRTUswithPLC-likefeaturesandviceversa.TheindustryhasstandardizedontheIEC61131-3functionalblocklanguageforcreatingprogramstorunonRTUsandPLCs,althoughnearlyallvendorsalsoofferproprietaryalternativesandassociateddevelopmentenvironments.DigitalandanalogsignalsDigitalordiscretesignalsbehaveasbinaryswitches,yieldingsimplyanOnorOffsignal(1or0,TrueorFalse,respectively).Pushbuttons,limitswitches,andphotoelectricsensorsareexamplesofdevicesprovidingadiscretesignal.Discretesignalsaresentusingeithervoltageorcurrent,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.Analogsignalscanusevoltageorcurrentwithamagnitudeproportionaltothevalueoftheprocesssignal.Forexample,ananalog4-20mAor0-10

Vinputwouldbeconvertedintoanintegervalueof0-32767.Currentinputsarelesssensitivetoelectricalnoise(i.e.fromweldersorelectricmotorstarts)thanvoltageinputs.ExampleAsanexample,sayafacilityneedstostorewaterinatank.Thewaterisdrawnfromthetankbyanothersystem,asneeded,andourexamplesystemmustmanagethewaterlevelinthetank.Usingonlydigitalsignals,thePLChastwodigitalinputsfromfloatswitches(LowLevelandHighLevel).Whenthewaterlevelisabovetheswitchitclosesacontactandpassesasignaltoaninput.ThePLCusesadigitaloutputtoopenandclosetheinletvalveintothetank.WhenthewaterleveldropsenoughsothattheLowLevelfloatswitchisoff(down),thePLCwillopenthevalvetoletmorewaterin.OncethewaterlevelraisesenoughsothattheHighLevelswitchison(up),thePLCwillshuttheinlettostopthewaterfromoverflowing.Thisrungisanexampleofsealinlogic.Theoutputissealedinuntilsomeconditionbreaksthecircuit.|||LowLevelHighLevelFillValve||------[/]------|------[/]----------------------(OUT)---------|||||||||||FillValve|||------[]------||||||Ananalogsystemmightuseawaterpressuresensororaloadcell,andanadjustable(throttling)drippingoutofthetank,thevalveadjuststoslowlydripwaterbackintothetank.Inthissystem,toavoid'flutter'adjustmentsthatcanwearoutthevalve,manyPLCsincorporate"hysteresis"whichessentiallycreatesa"deadband"ofactivity.Atechnicianadjuststhisdeadbandsothevalvemovesonlyforasignificantchangeinrate.Thiswillinturnminimizethemotionofthevalve,andreduceitswear.Arealsystemmightcombinebothapproaches,usingfloatswitchesandsimplevalvestopreventspills,andaratesensorandratevalvetooptimizerefillratesandpreventwaterhammer.Backupandmaintenancemethodscanmakearealsystemverycomplicated.ProgrammingPLCprogramsaretypicallywritteninaspecialapplicationonapersonalcomputer,thendownloadedbyadirect-connectioncableoroveranetworktothePLC.TheprogramisstoredinthePLCeitherinbattery-backed-upRAMorsomeothernon-volatileflashmemory.Often,asinglePLCcanbeprogrammedtoreplacethousandsofrelays.UndertheIEC61131-3standard,PLCscanbeprogrammedusingstandards-basedprogramminglanguages.AgraphicalprogrammingnotationcalledSequentialFunctionChartsisavailableoncertainprogrammablecontrollers.Recently,theInternationalstandardIEC61131-3hasbecomepopular.IEC61131-3currentlydefinesfiveprogramminglanguagesforprogrammablecontrolsystems:FBD(Functionblockdiagram),LD(Ladderdiagram),ST(Structuredtext,similartothePascalprogramminglanguage),IL(Instructionlist,similartoassemblylanguage)andSFC(Sequentialfunctionchart).Thesetechniquesemphasizelogicalorganizationofoperations.WhilethefundamentalconceptsofPLCprogrammingarecommontoallmanufacturers,differencesinI/Oaddressing,memoryorganizationandinstructionsetsmeanthatPLCprogramsareneverperfectlyinterchangeablebetweendifferentmakers.Evenwithinthesameproductlineofasinglemanufacturer,differentmodelsmaynotbedirectlycompatible.HistoryOriginThePLCwasinventedinresponsetotheneedsoftheAmericanautomotivemanufacturingindustry.Programmablecontrollerswereinitiallyadoptedbytheautomotiveindustrywheresoftwarerevisionreplacedthere-wiringofhard-wiredcontrolpanelswhenproductionmodelschanged.BeforethePLC,control,sequencing,andsafetyinterlocklogicformanufacturingautomobileswasaccomplishedusinghundredsorthousandsofrelays,camtimers,anddrumsequencersanddedicatedclosed-loopcontrollers.Theprocessforupdatingsuchfacilitiesfortheyearlymodelchange-overwasverytimeconsumingandexpensive,astherelaysystemsneededtoberewiredbyskilledelectricians.In1968GMHydramatic(theautomatictransmissiondivisionofGeneralMotors)issuedarequestforproposalforanelectronicreplacementforhard-wiredrelaysystems.ThewinningproposalcamefromBedfordAssociatesofBedford,Massachusetts.ThefirstPLC,designatedthe084becauseitwasBedfordAssociates'eighty-fourthproject,wastheresult.BedfordAssociatesstartedanewcompanydedicatedtodeveloping,manufacturing,selling,andservicingthisnewproduct:Modicon,whichstoodforMOdularDIgitalCONtroller.OneofthepeoplewhoworkedonthatprojectwasDickMorley,whoisconsideredtobethe"father"ofthePLC.TheModiconbrandwassoldin1977toGouldElectronics,andlateracquiredbyGermanCompanyAEGandthenbyFrenchSchneiderElectric,thecurrentowner.Oneoftheveryfirst084modelsbuiltisnowondisplayatModicon'sheadquartersinNorthAndover,Massachusetts.ItwaspresentedtoModiconbyGM,whentheunitwasretiredafternearlytwentyyearsofuninterruptedservice.TheautomotiveindustryisstilloneofthelargestusersofPLCs,andModiconstillnumberssomeofitscontrollermodelssuchthattheyendwitheighty-four.DevelopmentEarlyPLCsweredesignedtoreplacerelaylogicsystems.ThesePLCswereprogrammedin"ladderlogic",whichstronglyresemblesaschematicdiagramofrelaylogic.ModernPLCscanbeprogrammedinavarietyofways,fromladderlogictomoretraditionalprogramminglanguagessuchasBASICandC.AnothermethodisStateLogic,aVeryHighLevelProgrammingLanguagedesignedtoprogramPLCsbasedonStateTransitionDiagrams.ManyoftheearliestPLCsexpressedalldecisionmakinglogicinsimpleladderlogicwhichappearedsimilartoelectricalschematicdiagrams.Theelectricianswerequiteabletotraceoutcircuitproblemswithschematicdiagramsusingladderlogic.Thisprogramnotationwaschosentoreducetrainingdemandsfortheexistingtechnicians.OtherearlyPLCsusedaformofinstructionlistprogramming,basedonastack-basedlogicsolver.ProgrammingEarlyPLCs,uptothemid-1980s,wereprogrammedusingproprietaryprogrammingpanelsorspecial-purposeprogrammingterminals,whichoftenhaddedicatedfunctionkeysrepresentingthevariouslogicalelementsofPLCprograms.Programswerestoredoncassettetapecartridges.Facilitiesforprintinganddocumentationwereveryminimalduetolackofmemorycapacity.TheveryoldestPLCsusednon-volatilemagneticcorememory.FunctionalityThefunctionalityofthePLChasevolvedovertheyearstoincludesequentialrelaycontrol,motioncontrol,processcontrol,distributedcontrolsystemsandnetworking.Thedatahandling,storage,processingpowerandcommunicationcapabilitiesofsomemodernPLCsareapproximatelyequivalenttodesktopcomputers.PLC-likeprogrammingcombinedwithremoteI/Ohardware,allowageneral-purposedesktopcomputertooverlapsomePLCsincertainapplications.SuppliersWellknownPLCbrandsincludeSiemens,Allen-Bradley,IDEC,ABB,Mitsubishi,Omron,Honeywell,SchneiderElectric,Saia-BurgessControls,andGeneralElectric.

可編程控制器摘自WikipediaPLC和輸入輸出接口的排布一臺PLC或者稱為程序控制器是用于機電一體化進程的全自動工控機，如對機械裝配流水線、汽車駕乘、照明系統(tǒng)的控制。PLC可用于許多不同的儀器設備上，比如：包裝機械和半導體儀器。PLC不同于平常使用的計算機，它的開發(fā)源自于大量的輸入與輸出信號的排布，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，不受震動和撞擊的影響。用于控制機械運作的程序被存儲在使用電池的記憶體或者具有閃存作用的存儲器中。PLC是典型的在線系統(tǒng)，在有輸入信號之后的很短的時間內(nèi)一定會有輸出，否則會有不必要的結果產(chǎn)生。PLC的作用：基于PLC的控制面板（控制設備的核心部分是PLC）。整個面板是由幾個具有獨立功能的模塊組成，從左到右：電源，控制器，繼電器等……實現(xiàn)了輸入到輸出的功能。PLC與普通計算機之間的主要區(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進行信號的輸入輸出。這些接口連接了PLC和傳感器與激勵端口。PLC能夠讀取限位開關信號；模擬工藝參數(shù)（比如溫度和壓強），和對整個系統(tǒng)各個部件定位。一些PLC甚至可以用于機械動作的模擬。作為激勵端，PLC控制了電機，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PLC上，PLC也可以通過特定的模塊來連接控制端的微機。系統(tǒng)的數(shù)量范圍一臺小型PLC有一定數(shù)量的輸入輸出端口。作為PLC的一大特點，當主機輸入輸出接口數(shù)量不夠的時候，可以外接擴展端口。PLC的擴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)特定的用途來選擇。一些個別的模塊可以有一臺獨立的處理器來直接驅動，并且可以容納大量的輸入輸出信號。為了降低大型工廠的配線成本，一種特制的高速I/O接口被廣泛應用以使那些獨立的模塊可以與主處理器分放在不同的位置。用戶界面：PLC需要在外觀結構，報警記錄，以及日常的控制上適應操作者。人機界面（HMI）實現(xiàn)了這樣的目的，HMI與MMI和GUI屬于同一類型的操作界面。為了適應操作者，一個簡單的系統(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。許多復雜的編譯程序和監(jiān)控軟件都安裝在計算機上，該計算機與PLC通過數(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。同時自動通信協(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)可以通過網(wǎng)絡與另一臺PLC的系統(tǒng)通信，正如一臺電腦運行SCADA（數(shù)據(jù)采集與監(jiān)視控制系統(tǒng)）或者運行一個網(wǎng)頁瀏覽器。在大流量輸入輸出系統(tǒng)中，兩臺PLC之間的通信采用了P2P（對等聯(lián)網(wǎng)）技術。這讓獨立的幾個復雜進程能夠在當子系統(tǒng)在相互通信的時候被單獨控制。這種通信方式也常使用于人機交互界面，比如鍵盤或者計算機工作站。當今世界上已經(jīng)有部分的PLC支持更廣泛的信號傳輸方式，包括RS-485接口，同步傳輸，甚至可以當網(wǎng)絡傳輸速度達到100Mbit/s時利用以太網(wǎng)直接使用計算機控制.PLC與其他控制系統(tǒng)的比較PLC能夠很好的適應大部分自動化控制任務。在傳統(tǒng)工藝流水線上，開發(fā)以及維護全自動系統(tǒng)的成本要高于整個PLC控制系統(tǒng)，同時，現(xiàn)代工業(yè)正期待這樣的轉變。PLC自帶的輸入輸出設備使得工業(yè)控制器和設備得到了很好的協(xié)調(diào)；微電子技術在現(xiàn)代工業(yè)被廣泛的需求，設計中心采用了梯形圖（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PLC設備的成本比同級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，在這個系統(tǒng)中，大量一次性電器電源被集成在一起不同的技術用于大信息容量或者簡單的自動控制系統(tǒng)中。例如：一臺家用洗碗機所使用的機電一體化時序控制器的成本僅為幾美元。一臺基于微型控制器的設計將會因為使用用途廣泛使得整個工程的開發(fā)經(jīng)費（電源的設計以及輸入輸出設備的成本）分攤到各個商業(yè)領域，并且終端用戶無需修改其中的控制程序。自動分類系統(tǒng)便是一個典型的例子；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（運輸巴士）從經(jīng)濟的角度上出發(fā)使用PLC而不是定制控件系統(tǒng)，因為有較低的信息存儲量和并不低廉的開發(fā)成本。非常復雜的程序控制，一般用于化工業(yè)，需要一系列的運算法則，即使是高性能的PLC也是很難達到的。極高的運算速度和運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動控制系統(tǒng)中被廣泛應用，定位控制和控制扭矩。一些制造商把運動控制單元與PLC結合生成G代碼（在數(shù)控機床中被運用）以用于對機械運動的控制。正如操作臺一樣，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PID循環(huán)可用于對制造過程中的溫度控制。傳統(tǒng)的PLC常常僅配置了簡單的操作系統(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)如此強大，有關與PLC以及DCS系統(tǒng)的相關軟件少之又少。PLC在使用的廣泛性上與遠程終端設備（RTU）有著相似之處。然而RTU并不支持函數(shù)計算和反饋系統(tǒng)。由于硬件變得更加強大而且廉價，RTU,PLC,以及DCS的發(fā)展在功能上已經(jīng)相互補足了，許多廠商將RTU設備嵌入PLC界面中，同樣反之亦然。工業(yè)上已經(jīng)對IEC61131-3的功能模塊的編譯語言進行了規(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)字與模擬信號數(shù)字信號（離散信號）一般為二進制轉換，僅受開關信號（1或者0；正確或錯誤；識別）的影響。按鈕，限位開關，光電傳感器都是輸出離散信號的典型元器件。離散信號通過電壓或者電流傳輸，當電壓或者電流在指定范圍內(nèi)接通反之或者斷開。例如，一臺使用24v直流電源的PLC的輸入輸出接口，當電壓大于22V的時候接口接通，當直流電壓低于2V的時候接口斷開，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）。模擬信號的控制與音量的控制類似，有一個大小的零位和上限，在PLC上被認為是計數(shù)器，依靠驅動器具有廣泛的調(diào)整空間和精度并且一系列的數(shù)據(jù)可以被存儲下來。典型的PLC使用16進制處理器，信號數(shù)值的范圍在-32768至+32767之間。壓強，溫度，流量，以及重量可以被轉化為模擬信號。通過電流或電壓可以按比例放大或縮小模擬信號。例如：一個4~20毫安或者0~10伏的輸入模擬信號可通過轉換獲得的值可任意在0~32767范圍之間。電流輸入信號的抗電磁干擾能力要強于電壓輸入信號。范例舉個例子，假定某個設備需要將水存儲在水槽中。水槽的水能夠在需要的時候被某個系統(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，PLC的兩種輸入信號來浮球開關（高電平和低電平），當水位高于限位開關時，開關自動切斷進水信號。PLC利用數(shù)字脈沖輸出控制水槽的進出閥門。當水位足夠低的時候，低水位限位開關將會斷開，PLC將會打開進水閥門。當水位過高時，高水位限位開關將會接通，PLC將會關閉進水閥門。這是一個閉環(huán)控制系統(tǒng)的例子。當某些環(huán)節(jié)受到干擾的時候輸出會被斷開。|||低電平高電平滿水||------[/]------|------[/]----------------------(OUT)---------||