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Passive infrared detector



Briefdescription

Relatedtypes:

Indoorpassiveinfrared:Thedetectiondistancerangesfrom25cmto20meters.

Indoorcurtaintype:Thedetectiondistancerangesfrom25cmto20meters.

Outdoorpassiveinfrared:thedetectiondistancerangesfrom10metersto150meters.

Outdoorpassiveinfraredcurtaindetector:thedistancerangesfrom10metersto150meters.

Workingprinciple

Thecorecomponentofapassiveinfrareddetectorisapyroelectricsensor.Itsmainbodyisathin-filmferroelectricmaterial,whichispolarizedundertheactionofanexternalelectricfield.Whenanelectricfieldisapplied,thepolarizationstateisstillmaintained,whichiscalledspontaneouspolarization.SpontaneouspolarizationandtemperaturehaveCuriepointtemperature.AttheCuriepointtemperature,apyroelectricsensorismanufacturedaccordingtotherelationshipbetweenpolarizationintensityandtemperature.Whenacertainintensityofinfraredradiationreachesthepolarizedferroelectricmaterial,thetemperatureofthethinskinwillrise,thepolarizationintensitywilldecrease,andthesurfacepolarizationchargewilldecrease.Thispartofthechargeisconvertedintoanoutputvoltagebytheamplifier.Iftheradiationofthesameintensitycontinuestobeirradiated,thetemperatureoftheferroelectricmaterialstabilizesatacertainpointandnomorechargeisreleased,thatis,thereisnovoltageoutput.Sincethepyroelectricsensoronlyhasavoltagesignaloutputduringthetemperatureriseandfall,theopticalsystemofthepassiveinfrareddetectormustnotonlyhavetheabilitytoconcentrateinfraredradiation,butalsoallowtheheatradiatedonthepyroelectricsensortoriseandfall.,Toensurethatthepassiveinfrareddetectorhasavoltagesignaloutputwhensomeoneinvades.Inthedigitalpassiveinfrareddetector,theweakelectricalsignaloutputbythepyroelectricsensorisdirectlyinputtoapowerfulmicroprocessor,andallsignalconversion,amplification,filtering,etc.arecarriedoutinaprocessingchip,therebyimprovingthepassiveinfraredThereliabilityofthedetector.

Activeinfrareddetector

Activeinfrareddetectoriscomposedoftwoparts:receivingandtransmittingdevice.Thetransmittingdeviceradiatesabeamofinfraredraystothereceivingdeviceinstalledafewmetersorevenhundredsofmetersaway.Whenitisblocked,thereceivingdevicewillsendoutanalarmsignal.Therefore,itisalsoablockingalarmorathrough-beamdetector.Usually,thetransmittingdeviceiscomposedofamultivibrator,awaveformconversioncircuit,aninfraredlight-emittingtube,andanopticallens.Theoscillatorgeneratesapulsesignal,afterthewaveformistransformedandamplified,theinfraredlight-emittingtubeiscontrolledtogenerateinfraredpulselight,andtheinfraredlightischangedintoathininfraredbeamthroughthefocusinglens,whichisdirectedtothereceivingend. 

Thereceivingdeviceiscomposedofopticallens,infraredphotoelectrictube,magnifyingandshapingcircuit,powerdriverandactuator.Thephotoelectrictubeconvertsthereceivedinfraredlightsignalintoanelectricsignal,andaftershapingandamplifyingit,theactuatorispushedtostartthealarmdevice.Activeinfraredalarmshavealongtransmissiondistance.Becauseinfraredlightisanon-visiblelightsource,itisdifficultforintruderstodetectandavoid,andthedefensiveboundaryisveryclear.Activeinfraredalarmisapoint-typeandline-typedetectiondevice.Inadditiontobeingusedasasingle-unitpointandlinewarning,inordertoeffectivelypreventitinalargerarea,itcanalsousemultipleunitstoinstallalightwalloropticalnetworktoformawarningBlockadeorsecurityblockadenetwork,andevenformathree-dimensionalsecurityzone.Asingleopticalrouteconsistsofatransmitterandareceiver. 

Dualopticalroutingconsistsoftwopairsoftransmittersandreceivers.Thetwopairsofreceivingandtransmittingdevicesareopposedtoeachothertoeliminatecrossmisfires;multipleopticalpathsconstituteawarningsurface;andasinglereflectiveopticalpathconstitutesawarningarea.  

Passiveinfraredalarm

Passiveinfraredalarmdoesnotradiateenergyintospace,butinsteadreliesonreceivinginfraredradiationfromthehumanbodytogiveanalarm.Anyobjectwithtemperatureisconstantlyradiatinginfraredraystotheoutsideworld.Thesurfacetemperatureofthehumanbodyis36-27°C,andmostofitsradiationenergyisconcentratedinthewavelengthrangeof8-12um.Passiveinfraredalarmcanbedividedintoinfrareddetector(infraredprobe)andalarmcontrolpartinstructure.Themostcommonlyusedinfrareddetectorisapyroelectricdetector,whichisasensorthatconvertshumaninfraredradiationintoelectricity.Ifhumaninfraredradiationisdirectlyirradiatedonthedetector,ofcourseitwillalsocausetemperaturechangesandoutputsignals,butinthisway,thedetectiondistancewillnotbefar.Inordertolengthenthedetectionrangeofthedetector,anadditionalopticalsystemisrequiredtocollectinfraredradiation.Usually,aplasticmetal-platedopticalreflectionsystemoraplasticFresnellensisusedastheinfraredradiationfocusingsystem.Inthedetectionarea,theinfraredradiationenergyofthehumanbodythroughtheclothingisreceivedbythelensofthedetectorandfocusedonthepyroelectricsensor.Whenthehumanbody(intruder)movesinthismonitoringrange,itentersacertainfieldofviewonebyone,andthenwalksoutofthisfieldofview.Thepyroelectricsensorcanseethemovinghumanbodyforawhile,butnotforawhile,sothehumanbodyTheinfraredradiationcontinuouslychangesthetemperatureofthepyroelectricbody,causingittooutputoneafteranothercorrespondingsignal,whichisthealarmsignal. 

Themainfeaturesofthepassiveinfraredalarmareasfollows: 

Becauseitispassiveanddoesnotactivelyemitinfraredrays,itspowerconsumptionisverysmallanditiseasytoinstall.   

Comparedwithmicrowavealarms,infraredwavelengthscannotpassthroughordinarybuildingssuchasbricksandcement.Whenusedindoors,thereisnoneedtoworryaboutfalsealarmscausedbyoutdoormovingtargets.Wheninstallingmultiplepassiveinfraredalarmsinalargeareaindoors,becauseitispassive,itwillnotcausetheproblemofsystemmutualinterference.   

Theworkisnotaffectedbythesound,thatis,thesoundwillnotcauseittoproducefalsealarms.   

Systemdesignpoints 

Thelayoutofpassiveinfrareddetectors: 

Accordingtothefielddetectormode,itcanbedirectlyinstalledonthewall,ceilingorcorner.     

Payattentiontothedetectionrangeandhorizontalviewingangleofthedetectorwhenlayingout.      

Donotaimthedetectorattheheaterorair-conditioningoutletduct.     

Donotaimthedetectoratstronglightsources,doorsandwindowsexposedtodirectsunlight.  

Becarefulnottohavetallobstructionsorinterferencefromelectricfanbladesinthewarningarea,anddonotinstallitinaplacewithstrongelectricity.

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