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1、中文3475字ControlDevicesandPLCJosephLaFauciFromWikipedia,thefreeencyclopediaSeveraltypesofcontroldevicesareusedinindustrytosatisfythefollowingcontrolneeds.MechanicalControl、PneumaticControl、ElectromechanicalControl、ElectronicControl、ComputerControl、ProgrammableLogicC
2、ontrol(PLC)Mechanicalcontrolincludescamsandgovernors.Althoughtheyhavebeenusedforthecontrolofverycomplexmachines,tobecosteffectively,todaytheyareusedforsimpleandfixed-cycletaskcontrol.Someautomatedmachines,suchasscrewmachines,stillusecam-basedcontrol.Mechanicalcont
3、rolisdifficulttomanufactureandissubjecttowear.Pneumaticcontrolisstillverypopularforcertainapplications.Itusescompressedair,valves,andswitchestoconstructsimplecontrollogic,butisrelativelyslow.Becausestandardcomponentsareusedtoconstructthelogic,itiseasiertobuildthan
4、amechanicalcontrol.Pneumaticcontrolpartsaresubjecttowear.Asdoesamechanicalcontrol,anelectromechanicalcontroluseswitches,relays,timers,counters,andsoon,toconstructlogic.Becauseelectriccurrentisused,itisfasterandmoreflexible.Thecontrollersusingelectromechanicalcontr
5、olarecalledrelaydevices.Electriccontrolissimilartoelectromechanicalcontrol,exceptthatthemovingmechanicalcomponentsinanelectromechanicalcontroldevicearereplacedbyelectronicswitches,whichworksfasterandismorereliable.Computercontrolisthemostversatilecontrolsystem.The
6、logicofthecontrolisprogrammedintothecomputermemoryusingsoftware.Itnotonlycanbeformachineandmanufacturingsystemcontrol,butalsofordatacommunication.Verycomplexcontrolstrategieswithextensivecomputationscanbeprogrammed.Thefirstistheinterfacewiththeoutsideworld.Interna
7、lly,thecomputerusesalowvoltage(5to12volts)andalowcurrent(severalmilliamps).Machinerequiresmuchhighervoltages(24,110,or220voltages)andcurrents(measuredinamps).Theinterfacenotonlyhastoconvertthevoltagedifference,butalsomustfilterouttheelectricnoiseusuallyfoundinthes
8、hop.Theinterfacethusmustbecustom-builtforeachapplication.Inordertousetheadvantagesofallthosecontrollersandeliminatethedifficulties,theprogrammablelogicc
