可编程控制器 毕业论文外文翻译

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1、B：外文文献及译文SystemBlockDiagramAProgrammableControllerisaspecializedcomputer.Sinceitisacomputer,ithasallthebasiccomponentpartsthatanyothercomputerhas;aCentralProcessingUnit,Memory,InputInterfacingandOutputInterfacing.AtypicalprogrammablecontrollerblockdiagramisshowninFigure1.Figure1Programmable

2、ControllerBlockDiagramTheCentralProcessingUnit(CPU)isthecontrolportionofthePLC.Itinterpretstheprogramcommandsretrievedfrommemoryandactsonthosecommands.InpresentdayPLC'sthisunitisamicroprocessorbasedsystem.TheCPUishousedintheprocessormoduleofmodularizedsystems.Memoryinthesystemisgenerallyoft

3、wotypes;ROMandRAM.TheROMmemorycontainstheprograminformationthatallowstheCPUtointerpretandactontheLadderLogicprogramstoredintheRAMmemory.RAMmemoryisgenerallykeptalivewithanon-boardbatterysothatladderprogrammingisnotlostwhenthesystempowerisremoved.Thisbatterycanbeastandarddrycellorrechargeabl

4、enickel-cadmiumtype.NewerPLCunitsarenowavailablewithElectricallyErasableProgrammableReadOnlyMemory(EEPROM)whichdoesnotrequireabattery.Memoryisalsohousedintheprocessormoduleinmodularsystems.Inputunitscanbeanyofseveraldifferenttypesdependingoninputsignalsexpectedasdescribedabove.Whenpowerisap

5、pliedtoaprogrammablelogiccontroller,thePLC’soperationconsistsoftwosteps:(1)updateinputsandoutputsand(2)solvetheladder.ThefirstthingthePLCdoeswhenitbeginstofunctionisupdateI/O.Thismeansthatalldiscreteinputstatesarerecordedfromtheinputunitandalldiscretestatestobeoutputaretransferredtotheoutpu

6、tunit.Registerdatagenerallyhasspecificaddressesassociatedwithitforbothinputandoutputdatareferredtoasinputandoutputregisters.Theseregistersareavailabletotheinputandoutputmodulesrequiringthemandareupdatedwiththediscretedata.Sincethisisinput/outputupdating,itisreferredtoasI/O.AftertheI/Oupdate

7、hasbeenaccomplished,thePLCbeginsexecutingthecommandsprogrammedintoit.Thesecommandsaretypicallyreferredtoastheladderdiagram.Theladderdiagramisbasicallyarepresentation5oftheprogramstepsusingrelaycontactsandcoils.Theladderisdrawnwithcontactstotheleftsideoft