人體熱釋電紅外傳感器PIR原理

人體熱釋電紅外傳感器PIR原理詳解在電子防盜、人體探測器領域中，被動式熱釋電紅外探測器的應用非常廣泛，因其價格低廉、技術性能穩(wěn)定而受到廣大用戶和專業(yè)人士的歡迎。被動式熱釋電紅外探頭的工作原理及特性：人體都有恒定的體溫，一般在37度，所以會發(fā)出特定波長10μm左右的紅外線，被動式紅外探頭就是靠探測人體發(fā)射的10μm左右的紅外線而進行工作的。人體發(fā)射的10μm左右的紅外線通過菲涅爾濾光片增強后聚集到紅外感應源上。紅外感應源通常采用熱釋電元件，這種元件在接收到人體紅外輻射溫度發(fā)生變化時就會失去電荷平衡，向外釋放電荷，后續(xù)電路經(jīng)檢測處理后就能產(chǎn)生報警信號。(1)這種探頭是以探測人體輻射為目標的。所以熱釋電元件對波長為10μm左右的紅外輻射必須非常敏感。(2)為了僅僅對紅外輻射敏感，在它的輻射照面通常覆蓋有特殊的菲涅爾濾光片，使環(huán)境的干擾受到明顯的控制作用。(3)被動紅外探頭，其傳感器包含兩個互相串聯(lián)或并聯(lián)的熱釋電元。而且制成的兩個電極化方向正好相反，環(huán)境背景輻射對兩個熱釋元件幾乎具有相同的作用，使其產(chǎn)生釋電效應相互抵消，于是探測器無信號輸出。(4)一旦人侵入探測區(qū)域內，人體紅外輻射通過部分鏡面聚焦，并被熱釋電元接收，但是兩片熱釋電元接收到的熱量不同，熱釋電也不同，不能抵消，經(jīng)信號處理而報警。(5)菲涅爾濾光片根據(jù)性能要求不同，具有不同的焦距(感應距離)，從而產(chǎn)生不同的監(jiān)控視場，視場越多，控制越嚴密。被動式熱釋電紅外探頭的優(yōu)缺點：優(yōu)點：本身不發(fā)任何類型的輻射，器件功耗很小，隱蔽性好。價格低廉。缺點：◆容易受各種熱源、光源干擾◆被動紅外穿透力差，人體的紅外輻射容易被遮擋，不易被探頭接收?！粢资苌漕l輻射的干擾?！舡h(huán)境溫度和人體溫度接近時，探測和靈敏度明顯下降，有時造成短時失靈?？垢蓴_性能：1.防小動物干擾探測器安裝在推薦地使用高度，對探測范圍內地面上地小動物，一般不產(chǎn)生報警。2.抗電磁干擾探測器的抗電磁波干擾性能符合GB10408中4.6.1要求，一般手機電磁干擾不會引起誤報。3.抗燈光干擾探測器在正常靈敏度的范圍內，受3米外H4鹵素燈透過玻璃照射，不產(chǎn)生報警。紅外線熱釋電傳感器的安裝要求：紅外線熱釋電人體傳感器只能安裝在室內，其誤報率與安裝的位置和方式有極大的關系，正確的安裝應滿足下列條件：1.紅外線熱釋電傳感器應離地面2.0-2.2米。2.紅外線熱釋電傳感器遠離空調,冰箱，火爐等空氣溫度變化敏感的地方。3.紅外線熱釋電傳感器探測范圍內不得隔屏、家具、大型盆景或其他隔離物。Thisisatypicalapplicationcircuitthatdrivesarelay.R10andC6adjusttheamountoftimethatRY1remainsenergizedaftermotionisdetected.DownloadPDFdrawing.

FresnelLens_____________AFresnellens(pronouncedFrennel)isaPlanoConvexlensthathasbeencollapsedonitselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchsmallerinthicknessandthereforehaslessabsorptionlosses.OurFL65FresnellensismadeofaninfraredtransmittingmaterialthathasanIRtransmissionrangeof8to14umwhichismostsensitivetohumanbodyradiation.ItisdesignedtohaveitsgroovesfacingtheIRsensingelementsothatasmoothsurfaceispresentedtothesubjectsideofthelenswhichisusuallytheoutsideofanenclosurethathousesthesensor.Thelenselementisroundwithadiameterof1inchandhasaflangethatis1.5inchessquare.Thisflangeisusedformountingthelensinasuitableframeorenclosure.MountingcanbestandmosteasilybedonewithstripsofScotchtape.Siliconerubbercanalsobeusedifitoverlapstheedgestoformacaptivemount.TheFL65hasafocallengthof0.65inchesfromthelenstothesensingelement.Ithasbeendeterminedbyexperimenttohaveafieldofviewofapproximately10degreeswhenusedwithaPIR325Pyroelectricsensor.

ThisrelativelyinexpensiveandeasytousePyroelectricSensorandFresnelLenscanbeusedinavarietyofscienceprojects,robotsandotherusefuldevices.FocusingdevicesforpyroelectricinfraredsensorsPyroelectricinfraredsensorsFirstwewilllookatapyroelectricinfraredsensorandseehowitismadeandwhyafocusingdeviceisnecessary.Acommonlyusedpyroelectricinfraredsensorhastwosensingelementsinternallyconnectedinavoltagebuckingconfiguration.ApyroelectricsensorhasaninfraredfilterwindowthatadmitsIRwithinthe5to15micrometerwavelengthrange.Oneendofthetwoseries-connectedelementsinananalogsensorisconnectedtopin3thatisnormallygrounded.TheotherendconnectsinternallytothegateofaFieldEffectTransistorandtoaveryhighvaluepulldownresistor.PowerisappliedtoFETdrainpin1andtheoutputsignalcomesfromFETsourcepin2whichusuallyconnectsthroughanexternalpulldownresistortogroundandtoanamplifier.Adigitalsensornotshownhere,includesinternalprocessingcircuitsandoutputsdigitalpulses.ThesensorishousedinaTO5typepackage.Sensingelementsareeach0.039inch(1mm)wideandarespaced0.039inch(1mm)apart.Environmentalconditionssuchastemperaturechangesandsunlightwillaffectbothelements

simultaneouslyandwillproducethesameamountofoutputfromeachelementbutofopposingpolarityandwillthereforebecancelled.Thesensorwillonlyproduceachangeinitsoutputvoltagewhenoneofitselementsisexposedtoachangeinradiationandtheotherisnotexposed.AnIRemittingbodymovingacrossthefrontofasensorwillexposefirstone,thenbothandthentheothersensorelement.Theoutputsignalwaveformfromananalogsensorshowsthatformotioninonedirection,firstapositive,thenzeroandthenanegativetransitionresults.Motionintheotherdirectionwillproducefirstanegative,thenzeroandthenapositivetransition.WhenalensisnotusedinfrontofasensorandanIRemittingbodyisclosetothesensor,about3or4feetanditmovesacrossthefrontofthesensor,theradiatedIRwillexposeoneelementmorethantheotherandavoltageoutputwillresult.However,whentheIRemittingbodyisfurtherawayfromthesensoritsradiationpatternbecomesblurredandbothelementsareexposedmoreequally,resultinginnovoltageoutput.Thelimiteddetectionrangeisduetoalackofunequalexposure.Placingalensinfrontofthesensorextendsitsdetectionrange.TheFresnellensAFresnellensisaPlanoConvexlensthathasbeencollapsedonitselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchthinnerandthereforehaslessabsorptionloss.AFresnellensisusuallythinandflexibleandisabout0.015inch(0.38mm)thickwithgroovesmoldedintoonesurface.ThegroovesideofthelensusuallyfacesthePIRsensor.AFresnellensbothcapturesmoreIRradiationandfocusesittoasmallpoint.ThisfocalpointmovesacrossthesensorastheIRsourcemovesandexposesoneelementatatime.AFresnellenscanextenddetectionrangetoabout100feet.AFresnellenswillgivethebestpossibleperformance,howeverotherdevicescanbeusedtoextendrange.Althoughthefollowingdevicesmaynotfitthedescriptionofalens,wewillcallthemlensesanyway.ThisdiagramshowsIRexposingbothelementsequallywhennolensisused.ShadowlensSincesimultaneousexposureofbothelementsisthecauseoflimiteddetectionrange,allweneedissomemethodofpreventingtheIRfromexposingbothelementssimultaneouslyastheIRemittingbodymovesacrossthefrontofthesensor,evenatgreaterdistancesfromthesensor.Thesensorelementsare0.039inch(1mm)wideandarespaced0.039inch(1mm)apart.IfweplaceathinverticalstripofIRopaquematerialabout0.060inch(1.5mm)widecenteredinfrontofthesensorwecanpreventsomeoftheIRfromstrikingthesurfaceofthesensorbyproducingashadow,eveniftheIRemittingbodyisatagreaterdistancefromthesensor.ThefollowingfigureshowssuchabafflebutinthisexampletheIRstillexposesbothelementsequally.Byplacingabaffleormaskinfrontofthesensor,wecanblocksomeoftheIRandproduceashadowonthesensorThisnextfigureshowswhathappenswhentheIRemittingbodymovesacrossthefrontofthesensorevenatgreaterdistances.Thebaffleallowsfullexposureofelement1whileblockingtheIRsoitproducesashadowoverelement2anddoesnotexposeit.Thissimplelensextendsdetectionrangeupto20feetandiseasilymadefromastripofpaperorothermaterial.Thebafflecanbespaced1/2inch(12mm)to1inch(25mm)infrontofthesensor.Thegreaterspacinggivesanarrowerdetectionangle.AstheIRsourcemoves,thebaffleblocksitfromexposingoneofthesensorelementswhilefullyexposingtheother.Thissameideacanbeexpandedtoproduceawideanglelens.MultiplebafflestripscanbeplacedinfrontofthesensortoalternatelyblockIRfromonesensorelementatatimeevenwhentheIRemittingbodyisatgreateranglestothefrontofthesensor.Thismultiplebaffleshadowlensprovidesawidedetectionangle.Thelensshouldbecurvedsoallbafflesarethesamedistancefromthefrontofthesensor.PinholelensAnothersimplefocusingdevicethatwillexposeonePIRsensorelementatatimecanbemadeusingathinpieceofIRopaquematerialwithaholeinitthatwillfunctionasapinholelenssimilartothelensofapinholecamera.

Thefunctionofapinholecameralensisdescribedin/question131.htm.

ThelensholeinacameraisusuallysmallbutcanbemuchlargerinasensorapplicationwhereimagedetailisnotnecessaryandonlytheIRradiationfromtheanimalmustbefocusedontoonesensingelementatatime.IRinthe5~15micrometerwavelengthrangewillnotpassthroughmostmaterialssoyoucanmakealensofpaper,plasticormetalfoil.Theholeshouldbeaboutinch(6.4mm)diameter.Lensspacingisnotcriticalbutitshouldbeaboutinch(12mm)to1inch(25mm)fromthefrontofthesensor.Adetectionrangeofupto20feetcanbeobtainedwiththistypeoflens.

Althoughanarrowfieldofviewisusuallymostdesirableforanimalphotos,awidefieldofviewcanbeobtainedbyplacingseveralholesinthelensmaterialandcurvingthelensinfrontofthesensorsoallholesareanequaldistancefromthefrontofthesensor.Anothertypeoflenscanbemadebyplacingatubeabout3/8inch(10mm)diameterand2inch(50mm)longoverthefrontofthesensor.

Thislenswillhaveanarrowfieldofview.InfraredwindowApyroelectricsensorisverysensitivetorapidtemperaturechanges.Arapidchangeinairtemperatureduetoabreezefromanopenwindoworfromanairconditionerorheatercancausefalsetriggering.Theshadowandpinholelensesdescribedabovedonotofferprote