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1、LADDERLOGIC"Ladder"diagramsLadderdiagramsarespecializedschematicscommonlyusedtodocumentindustrialcontrollogicsystems.Theyarecalled"ladder"diagramsbecausetheyresemblealadder,withtwoverticalrails(supplypower)andasmany"rungs"(horizontallines)astherearecontrolcircuitstorepresent.Ifwewanted
2、todrawasimpleladderdiagramshowingalampthatiscontrolledbyahandswitch,itwouldlooklikethis:The"L1"and"L2"designationsrefertothetwopolesofa120VACsupply,unlessotherwisenoted.L1isthe"hot"conductor,andL2isthegrounded("neutral")conductor.Thesedesignationshavenothingtodowithinductors,justtomake
3、thingsconfusing.Theactualtransformerorgeneratorsupplyingpowertothiscircuitisomittedforsimplicity.Inreality,thecircuitlookssomethinglikethis:Typicallyinindustrialrelaylogiccircuits,butnotalways,theoperatingvoltagefortheswitchcontactsandrelaycoilswillbe120voltsAC.LowervoltageACandevenDCs
4、ystemsaresometimesbuiltanddocumentedaccordingto"ladder"diagrams:Solongastheswitchcontactsandrelaycoilsarealladequatelyrated,itreallydoesn'tmatterwhatlevelofvoltageischosenforthesystemtooperatewith.Notethenumber"1"onthewirebetweentheswitchandthelamp.Intherealworld,thatwirewouldbelabeled
5、withthatnumber,usingheat-shrinkoradhesivetags,whereveritwasconvenienttoidentify.Wiresleadingtotheswitchwouldbelabeled"L1"and"1,"respectively.Wiresleadingtothelampwouldbelabeled"1"and"L2,"respectively.Thesewirenumbersmakeassemblyandmaintenanceveryeasy.Eachconductorhasitsownuniquewirenum
6、berforthecontrolsystemthatit'susedin.Wirenumbersdonotchangeatanyjunctionornode,evenifwiresize,color,orlengthchangesgoingintooroutofaconnectionpoint.Ofcourse,itispreferabletomaintainconsistentwirecolors,butthisisnotalwayspractical.Whatmattersisthatanyone,electricallycontinuouspointinaco
7、ntrolcircuitpossessesthesamewirenumber.Takethiscircuitsection,forexample,withwire#25asasingle,electricallycontinuouspointthreadingtomanydifferentdevices:Inladderdiagrams,theloaddevice(lamp,relaycoil,solenoidcoil,etc.)isalmostalwaysdrawnattheright-handsideoftherung.Whileitdoesn'tmatte
