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1、PhotoelectricSensorsTheoryofOperationAphotoelectricsensorisanothertypeofpositionsensingdevice.Photoelectricsensors,similartotheonesshownbelow,useamodulatedlightbeamthatiseitherbrokenorreflectedbythetarget.Thecontrolconsistsofanemitter(lightsource),areceivertodetecttheemittedligh
2、t,andassociatedelectronicsthatevaluateandamplifythedetectedsignalcausingthephotoelectric’soutputswitchtochangestate.Weareallfamiliarwiththesimpleapplicationofaphotoelectricsensorplacedintheentranceofastoretoalertthepresenceofacustomer.This,ofcourse,isonlyonepossibleapplication.8
3、0ModulatedLightModulatedlightincreasesthesensingrangewhilereducingtheeffectofambientlight.Modulatedlightispulsedataspecificfrequencybetween5and30KHz.Thephotoelectricsensorisabletodistinguishthemodulatedlightfromambientlight.Lightsourcesusedbythesesensorsrangeinthelightspectrumfr
4、omvisiblegreentoinvisibleinfrared.Light-emittingdiode(LED)sourcesaretypicallyused.ClearanceItispossiblethattwophotoelectricdevicesoperatingincloseproximitytoeachothercancauseinterference.Theproblemmayberectifiedwithalignmentorcovers.Thefollowingclearancesbetweensensorsaregivenas
5、astartingpoint.Insomecasesitmaybenecessarytoincreasethedistancebetweensensors.SensorModelDistanceD4mm/M550mmM12250mmM18250mmK31250mmK30500mmK40750mmK80500mmL18150mmL50(Diffuse)30mmL50(Thru-Beam)80mm81ExcessGainManyenvironments,particularlyindustrialapplications,includedust,dirt,
6、smoke,moisture,orotherairbornecontaminants.Asensoroperatinginanenvironmentthatcontainsthesecontaminantsrequiresmorelighttooperateproperly.Therearesixgradesofcontamination:1.CleanAir(Idealcondition,climatecontrolledorsterile)2.SlightContamination(Indoor,nonindustrialareas,officeb
7、uildings)3.LowContamination(Warehouse,lightindustry,materialhandlingoperations)4.ModerateContamination(Millingoperations,highhumidity,steam)5.HighContamination(Heavyparticleladenair,extremewashdownenvironments,grainelevators)6.Extreme/SevereContamination(Coalbins,residueonlens)E
8、xcessgainrepresentstheamountoflightemittedbythe
