自动化英文文献翻译.docx

自动化英文文献翻译.docx

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自动化英文文献翻译

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Programmablelogiccontroller

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PLC&input/outputarrangements

Aprogrammablelogiccontroller（PLC）orprogrammablecontrollerisadigitalcomputerusedforautomationofelectromechanicalprocesses,suchascontrolofmachineryonfactoryassemblylines,controlofamusementrides,orcontroloflightingfixtures.PLCsareusedinmanydifferentindustriesandmachinessuchaspackagingandsemiconductormachines.Unlikegeneral-purposecomputers,thePLCisdesignedformultipleinputsandoutputarrangements,extendedtemperatureranges,immunitytoelectricalnoise,andresistancetovibrationandimpact.Programstocontrolmachineoperationaretypicallystoredinbattery-backedornon-volatilememory.APLCisanexampleofarealtimesystemsinceoutputresultsmustbeproducedinresponsetoinputconditionswithinaboundedtime,otherwiseunintendedoperationwillresult.

Features

ControlpanelwithPLC（greyelementsinthecenter）.Theunitconsistsofseparateelements,fromlefttoright;powersupply,controller,relayunitsforin-andoutput

ThemaindifferencefromothercomputersisthatPLCsarearmoredforsevereconditions（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.

Userinterface

Seealso:

Listofhuman-computerinteractiontopics

PLCsmayneedtointeractwithpeopleforthepurposeofconfiguration,alarmreportingoreverydaycontrol.

AHuman-MachineInterface（HMI）isemployedforthispurpose.HMIsarealsoreferredtoasMMIs（ManMachineInterface）andGUI（GraphicalUserInterface）.

Asimplesystemmayusebuttonsandlightstointeractwiththeuser.Textdisplaysareavailableaswellasgraphicaltouchscreens.Morecomplexsystemsuseaprogrammingandmonitoringsoftwareinstalledonacomputer,withthePLCconnectedviaacommunicationinterface.

Communications

PLCshavebuiltincommunicationsportsusually9-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.

PLCcomparedwithothercontrolsystems

PLCsarewell-adaptedtoarangeofautomationtasks.Thesearetypicallyindustrialprocessesinmanufacturingwherethecostofdevelopingandmaintainingtheautomationsystemishighrelativetothetotalcostoftheautomation,andwherechangestothesystemwouldbeexpectedduringitsoperationallife.PLCscontaininputandoutputdevicescompatiblewithindustrialpilotdevicesandcontrols;littleelectricaldesignisrequired,andthedesignproblemcentersonexpressingthedesiredsequenceofoperationsinladderlogic（orfunctionchart）notation.PLCapplicationsaretypicallyhighlycustomizedsystemssothecostofapackagedPLCislowcomparedtothecostofaspecificcustom-builtcontrollerdesign.Ontheotherhand,inthecaseofmass-producedgoods,