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附录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.

可编程控制器摘自WikipediaPLC和输入输出接口的排布一台PLC或者称为程序控制器是用于机电一体化进程的全自动工控机，如对机械装配流水线、汽车驾乘、照明系统的控制。PLC可用于许多不同的仪器设备上，比如：包装机械和半导体仪器。PLC不同于平常使用的计算机，它的开发源自于大量的输入与输出信号的排布，能够在较大的温度范围下保持良好的工作状态，不受电磁噪音的干扰，不受震动和撞击的影响。用于控制机械运作的程序被存储在使用电池的记忆体或者具有闪存作用的存储器中。PLC是典型的在线系统，在有输入信号之后的很短的时间内一定会有输出，否则会有不必要的结果产生。PLC的作用：基于PLC的控制面板（控制设备的核心部分是PLC）。整个面板是由几个具有独立功能的模块组成，从左到右：电源，控制器，继电器等……实现了输入到输出的功能。PLC与普通计算机之间的主要区别在于PLC能够在任何环境下保持良好的工作状态（包括有灰尘，潮湿，高温，低温等等）并且有许多闲置的接口可以用来进行信号的输入输出。这些接口连接了PLC和传感器与激励端口。PLC能够读取限位开关信号；模拟工艺参数（比如温度和压强），和对整个系统各个部件定位。一些PLC甚至可以用于机械动作的模拟。作为激励端，PLC控制了电机，汽缸或是液压缸，电磁继电器，螺线管，或者可以模拟输出。一系列的输入输出端口可以集成在一台PLC上，PLC也可以通过特定的模块来连接控制端的微机。系统的数量范围一台小型PLC有一定数量的输入输出端口。作为PLC的一大特点，当主机输入输出接口数量不够的时候，可以外接扩展端口。PLC的扩展模块都带有一种底盘（也可称为支架），根据不同的用途将模块放入不同的位置。不同模块的处理器和选择器的输入输出接口可根据特定的用途来选择。一些个别的模块可以有一台独立的处理器来直接驱动，并且可以容纳大量的输入输出信号。为了降低大型工厂的配线成本，一种特制的高速I/O接口被广泛应用以使那些独立的模块可以与主处理器分放在不同的位置。用户界面：PLC需要在外观结构，报警记录，以及日常的控制上适应操作者。人机界面（HMI）实现了这样的目的，HMI与MMI和GUI属于同一类型的操作界面。为了适应操作者，一个简单的系统需要具备按钮和显示。显示的程序可在触摸屏上直接调试。许多复杂的编译程序和监控软件都安装在计算机上，该计算机与PLC通过数据接口连接。通信方式PLC的通信接口一般采用9针的RS232接口，并且兼容RS485和以太网络接口。常用的通信协议包含了Modbus或者DF1。其他可供选择的也包括了不同的fieldbuses，例如devicenet或者profibus。同时自动通信协议已经包含了其他的通信协议。大多数最新的PLC已经可以通过网络与另一台PLC的系统通信，正如一台电脑运行SCADA（数据采集与监视控制系统）或者运行一个网页浏览器。在大流量输入输出系统中，两台PLC之间的通信采用了P2P（对等联网）技术。这让独立的几个复杂进程能够在当子系统在相互通信的时候被单独控制。这种通信方式也常使用于人机交互界面，比如键盘或者计算机工作站。当今世界上已经有部分的PLC支持更广泛的信号传输方式，包括RS-485接口，同步传输，甚至可以当网络传输速度达到100Mbit/s时利用以太网直接使用计算机控制.PLC与其他控制系统的比较PLC能够很好的适应大部分自动化控制任务。在传统工艺流水线上，开发以及维护全自动系统的成本要高于整个PLC控制系统，同时，现代工业正期待这样的转变。PLC自带的输入输出设备使得工业控制器和设备得到了很好的协调；微电子技术在现代工业被广泛的需求，设计中心采用了梯形图（或者功能表图）的程序编译方法。PLC的控制界面非常友好，整台PLC设备的成本比同级的特制控制器低出不少。从另一方面看，由于大批量生产，定制控件系统的开发源于生产成本的控制，定制控件系统将取代“一般的”解决方案，在这个系统中，大量一次性电器电源被集成在一起不同的技术用于大信息容量或者简单的自动控制系统中。例如：一台家用洗碗机所使用的机电一体化时序控制器的成本仅为几美元。一台基于微型控制器的设计将会因为使用用途广泛使得整个工程的开发经费（电源的设计以及输入输出设备的成本）分摊到各个商业领域，并且终端用户无需修改其中的控制程序。自动分类系统便是一个典型的例子；每年有大量的产品，仅仅有极少数的客户需要自主修改一些控制程序。然而，一些特制的汽车（运输巴士）从经济的角度上出发使用PLC而不是定制控件系统，因为有较低的信息存储量和并不低廉的开发成本。非常复杂的程序控制，一般用于化工业，需要一系列的运算法则，即使是高性能的PLC也是很难达到的。极高的运算速度和运算精度可能需要特殊的解决方案；例如宇宙飞船的飞行控制。程序控制器常常在运动控制系统中被广泛应用，定位控制和控制扭矩。一些制造商把运动控制单元与PLC结合生成G代码（在数控机床中被运用）以用于对机械运动的控制。正如操作台一样，PLC的逻辑系统为带有反馈的循环控制系统，一种“比例，积分，微分控制”或者是“PID控制”，例如一个PID循环可用于对制造过程中的温度控制。传统的PLC常常仅配置了简单的操作系统。处理器需要成百上千的循环，所以一种分布式控制系统（DCS）将取而代之。然而，即使PLC的功能已经如此强大，有关与PLC以及DCS系统的相关软件少之又少。PLC在使用的广泛性上与远程终端设备（RTU）有着相似之处。然而RTU并不支持函数计算和反馈系统。由于硬件变得更加强大而且廉价，RTU,PLC,以及DCS的发展在功能上已经相互补足了，许多厂商将RTU设备嵌入PLC界面中，同样反之亦然。工业上已经对IEC61131-3的功能模块的编译语言进行了规范化以便于在RTU和PLC上使用，尽管生产厂商已经向客户提供了编译软件。数字与模拟信号数字信号（离散信号）一般为二进制转换，仅受开关信号（1或者0；正确或错误；识别）的影响。按钮，限位开关，光电传感器都是输出离散信号的典型元器件。离散信号通过电压或者电流传输，当电压或者电流在指定范围内接通反之或者断开。例如，一台使用24v直流电源的PLC的输入输出接口，当电压大于22V的时候接口接通，当直流电压低于2V的时候接口断开，2V~22V中的电压并不确定接通或断开。最初的PLC只有离散型接口（数字接口）。模拟信号的控制与音量的控制类似，有一个大小的零位和上限，在PLC上被认为是计数器，依靠驱动器具有广泛的调整空间和精度并且一系列的数据可以被存储下来。典型的PLC使用16进制处理器，信号数值的范围在-32768至+32767之间。压强，温度，流量，以及重量可以被转化为模拟信号。通过电流或电压可以按比例放大或缩小模拟信号。例如：一个4~20毫安或者0~10伏的输入模拟信号可通过转换获得的值可任意在0~32767范围之间。电流输入信号的抗电磁干扰能力要强于电压输入信号。范例举个例子，假定某个设备需要将水存储在水槽中。水槽的水能够在需要的时候被某个系统抽出，我们的范例系统需要能够控制槽中水位。仅仅使用数字信号，PLC的两种输入信号来浮球开关（高电平和低电平），当水位高于限位开关时，开关自动切断进水信号。PLC利用数字脉冲输出控制水槽的进出阀门。当水位足够低的时候，低水位限位开关将会断开，PLC将会打开进水阀门。当水位过高时，高水位限位开关将会接通，PLC将会关闭进水阀门。这是一个闭环控制系统的例子。当某些环节受到干扰的时候输出会被断开。|||低电平高电平满水||------[/]------|------[/]----------------------(OUT)---------||