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.