人體熱釋電紅外傳感器PIR原理

word文檔精品文檔分享1.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(lǐng)域中，被動式熱釋電紅外探測器的應(yīng)用非常廣泛，因其價格低廉、技術(shù)性能穩(wěn)定而受到廣闊用戶和專業(yè)人士的歡送。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m左右的紅外線，被動式紅外探頭就是靠探測人體發(fā)射的10m左右的紅外線而進(jìn)展工作的。人體發(fā)射的10m左右的紅外線通過菲涅爾濾光片增強(qiáng)后聚集到紅外感應(yīng)源上。紅外感應(yīng)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(biāo)的。所以熱釋電元件對波長為10m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一樣的作用，使其產(chǎn)生釋電效應(yīng)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(nèi)，人體紅外輻射通過局部鏡面聚焦，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(yīng)距離)，從而產(chǎn)生不同的監(jiān)控視場，視場越多，控制越嚴(yán)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。抗干擾性能：防小動物干擾探測器安裝在推薦地使用高度，對探測X圍內(nèi)地面上地小動物，一般不產(chǎn)生報警?？闺姶鸥蓴_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(jī)電磁干擾不會引起誤報。抗燈光干擾探測器在正常靈敏度的X圍內(nèi)，受3米外H4鹵素?zé)敉高^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(nèi)，其誤報率與安裝的位置和方式有極大的關(guān)系，正確的安裝應(yīng)滿足以下條件：紅外線熱釋電傳感器應(yīng)離地面2.0-2.2米。紅外線熱釋電傳感器遠(yuǎn)離空調(diào),冰箱，火爐等空氣溫度變化敏感的地方。紅外線熱釋電傳感器探測X圍內(nèi)不得隔屏、家具、大型盆景或其他隔離物。word文檔精品文檔分享紅外線熱釋電傳感器不要直對窗口，否那么窗外的熱氣流擾動和人員走動會引起誤報，有條件的最好把窗簾拉上。紅外線熱釋電傳感器也不要安裝在有強(qiáng)氣流活動的地方。紅外線熱釋電傳感器對人體的敏感程度還和人的運(yùn)動方向關(guān)系很大。熱釋電紅外傳感器對于徑向移動反響最不敏感,而對于橫切方向(即與半徑垂直的方向)移動那么最為敏感.在現(xiàn)場選擇適宜的安裝位置是防止紅外探頭誤報、求得最正確檢測靈敏度極為重要的一環(huán)。2.菲涅爾透鏡2.1概述菲涅爾透鏡多是由聚烯烴材料注壓而成的薄片，鏡片外表一面為光面，另一面刻錄了由小到大的同心圓。菲涅爾透鏡的在很多時候相當(dāng)于紅外線及可見光的凸透鏡，效果較好，但本錢比普通的凸透鏡低很多。菲涅爾透鏡可按照光學(xué)設(shè)計或構(gòu)造進(jìn)展分類。菲涅爾透鏡作用有兩個：一是聚XX用；二是將探測區(qū)域內(nèi)分為假設(shè)干個明區(qū)和暗區(qū)，使進(jìn)入探測區(qū)域的移動物體能以溫度變化的形式在PIR〔被動紅外線探測器〕上產(chǎn)生變化熱釋紅外信號。2.2作用菲涅爾透鏡利用透鏡的特殊光學(xué)原理，在探測器前方產(chǎn)生一個交替變化的區(qū)替從強(qiáng)其能量幅度。菲涅爾透鏡菲涅爾透鏡，簡單的說就是在透鏡的一側(cè)有等距的齒紋，通過這些齒紋，可以到達(dá)對指定光譜X圍的光帶通(反射或者折射)的作用。傳統(tǒng)的打磨光學(xué)器材的帶通光學(xué)濾鏡造價昂貴。菲涅爾透鏡可以極大的降低本錢。典型的例子就是PIR。PIR廣泛的用在警報器上。如果你拿一個看看，你會發(fā)現(xiàn)在每個PIR上都有個塑料的小帽子。這就是菲涅爾透鏡。小帽子的內(nèi)部都刻上了齒紋。這種菲涅爾透鏡可以將入射光的頻率峰值限制到10微米左右〔人體紅外線輻射的峰值〕。菲涅耳透鏡可以把透過窄帶干預(yù)濾光鏡的光聚焦在硅光電二級探測器的光敏面上，菲涅爾透鏡不能用任何有機(jī)溶液(如酒精等)擦拭，除塵時可先用蒸餾水或普通凈水沖洗，再用脫脂棉擦拭。word文檔精品文檔分享3.HowInfraredmotiondetectorcomponentsworkInfraredRadiation_____________Infraredradiationexistsintheelectromagneticspectrumatawavelengththatislongerthanvisiblelight.Itcannotbeseenbutitcanbedetected.Objectsthatgenerateheatalsogenerateinfraredradiationandthoseobjectsincludeanimalsandthehumanbodywhoseradiationisstrongestatawavelengthof9.4um.Infraredinthisrangewillnotpassthroughmanytypesofmaterialthatpassvisiblelightsuchasordinarywindowglassandplastic.Howeveritwillpassthrough,withsomeattenuation,materialthatisopaquetovisiblelightsuchasgermaniumandsilicon.AnunprocessedsiliconwafermakesagoodIRwindowinaweatherproofenclosureforoutdooruse.Italsoprovidesadditionalfilteringforlightinthevisiblerange.9.4uminfraredwillalsopassthroughpolyethylenewhichisusuallyusedtomakeFresnellensestofocustheinfararedontosensorelements.PyroelectricSensors_____________Thepyroelectricsensorismadeofacrystallinematerialthatgeneratesasurfaceelectricchargewhenexposedtoheatintheformofinfraredradiation.Whentheamountofradiationstrikingthecrystalchanges,theamountofchargealsochangesandcanthenbemeasuredwithasensitiveFETdevicebuiltintothesensor.ThesensorelementsaresensitivetoradiationoverawiderangesoafilterwindowisaddedtotheTO5packagetolimitdetectableradiationtothe8to14mmrangewhichismostsensitivetohumanbodyradiation.Typically,theFETsourceterminalpin2connectsthroughapulldownresistorofabout100Ktogroundandfeedsintoatwostageamplifierhavingsignalconditioningcircuits.Theamplifieristypicallybandwidthlimitedtobelow10Hztorejecthighfrequencynoiseandisfollowedbyawindowcomparatorthatrespondstoboththepositiveandnegativetransitionsofthesensoroutputsignal.Awellfilteredpowersourceoffrom3to15voltsshouldbeconnectedtotheFETdrainterminalpin1.ThePIR325sensorhastwosensingelementsconnectedinavoltagebuckingconfiguration.Thisarrangementcancelssignalscausedbyvibration,temperatureword文檔精品文檔分享changesandsunlight.Abodypassinginfrontofthesensorwillactivatefirstoneandthentheotherelementwhereasothersourceswillaffectbothelementssimultaneouslyandbecancelled.Theradiationsourcemustpassacrossthesensorinahorizontaldirectionwhensensorpins1and2areonahorizontalplanesothattheelementsaresequentiallyexposedtotheIRsource.AfocusingdeviceisusuallyusedinfrontofthesensorThefigurebelowshowsthePIR325electricalspecificationsandlayoutinitsTO5package.Notethewideviewinganglewithoutanexternallens.word文檔精品文檔分享Thisisatypicalapplicationcircuitthatdrivesarelay.R10andC6adjusttheamountoftimethatRY1remainsenergizedaftermotionisdetected.DownloadPDFdrawing.word文檔精品文檔分享FresnelLens_____________AFresnellens(pronouncedFrennel)isaPlanoConvexlensthathasbeencollapsedonitselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchsmallerinthicknessandthereforehaslessabsorptionlosses.OurFL65FresnellensismadeofaninfraredtransmittingmaterialthathasanIRtransmissionrangeof8to14umwhichismostsensitivetohumanbodyradiation.ItisdesignedtohaveitsgroovesfacingtheIRsensingelementsothatasmoothsurfaceispresentedtothesubjectsideofthelenswhichisusuallytheoutsideofanenclosurethathousesthesensor.Thelenselementisroundwithadiameterof1inchandhasaflangethatis1.5inchessquare.Thisflangeisusedformountingthelensinasuitableframeorenclosure.MountingcanbestandmosteasilybedonewithstripsofScotchtape.Siliconerubbercanword文檔精品文檔分享alsobeusedifitoverlapstheedgestoformacaptivemount.TheFL65hasafocallengthof0.65inchesfromthelenstothesensingelement.Ithasbeendeterminedbyexperimenttohaveafieldofviewofapproximately10degreeswhenusedwithaPIR325Pyroelectricsensor.ThisrelativelyinexpensiveandeasytousePyroelectricSensorandFresnelLenscanbeusedinavarietyofscienceprojects,robotsandotherusefuldevices.3.1FocusingdevicesforpyroelectricinfraredsensorsA.1Pyroelectricinfraredsensorsword文檔精品文檔分享A.2Firstwewilllookatapyroelectricinfraredsensorandseehowitismadeandwhyafocusingdeviceisnecessary.Acommonlyusedpyroelectricinfraredsensorhastwosensingelementsinternallyconnectedinavoltagebuckingconfiguration.ApyroelectricsensorhasaninfraredfilterwindowthatadmitsIRwithinthe5to15micrometerwavelengthrange.Oneendofthetwoseries-connectedelementsinananalogsensorisconnectedtopin3thatisnormallygrounded.TheotherendconnectsinternallytothegateofaFieldEffectTransistorandtoaveryhighvaluepulldownresistor.PowerisappliedtoFETdrainpin1andtheoutputsignalcomesfromFETsourcepin2whichusuallyconnectsthroughanexternalpulldownresistortogroundandtoanamplifier.Adigitalsensornotshownhere,word文檔精品文檔分享includesinternalprocessingcircuitsandoutputsdigitalpulses.A.3ThesensorishousedinaTO5typepackage.Sensingelementsareeach0.039inch(1mm)wideandarespaced0.039inch(1mm)apart.A.4Environmentalconditionssuchastemperaturechangesandsunlightwillaffectbothelementssimultaneouslyandwillproducethesameamountofoutputfromeachelementbutofopposingpolarityandwillthereforebecancelled.Thesensorwillonlyproduceachangeinitsoutputvoltagewhenoneofitselementsisexposedtoachangeinradiationandtheotherisnotexposed.word文檔精品文檔分享AnIRemittingbodymovingacrossthefrontofasensorwillexposefirstone,thenbothandthentheothersensorelement.Theoutputsignalwaveformfromananalogsensorshowsthatformotioninonedirection,firstapositive,thenzeroandthenanegativetransitionresults.Motionintheotherdirectionwillproducefirstaword文檔精品文檔分享negative,thenzeroandthenapositivetransition.A.5WhenalensisnotusedinfrontofasensorandanIRemittingbodyisclosetothesensor,about3or4feetanditmovesacrossthefrontofthesensor,theradiatedIRwillexposeoneelementmorethantheotherandavoltageoutputwillresult.However,whentheIRemittingbodyisfurtherawayfromthesensoritsradiationpatternbecomesblurredandbothelementsareexposedmoreequally,resultinginnovoltageoutput.Thelimiteddetectionrangeisduetoalackofunequalexposure.Placingalensinfrontofthesensorextendsitsdetectionrange.A.6TheFresnellensA.7AFresnellensisaPlanoConvexlensthathasbeencollapsedonitselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchthinnerandthereforehaslessabsorptionloss.AFresnellensisusuallythinandflexibleandisabout0.015inch(0.38mm)thickwithword文檔精品文檔分享groovesmoldedintoonesurface.ThegroovesideofthelensusuallyfacesthePIRsensor.AFresnellensbothcapturesmoreIRradiationandfocusesittoasmallpoint.ThisfocalpointmovesacrossthesensorastheIRsourcemovesandexposesoneelementatatime.AFresnellenscanextendword文檔精品文檔分享detectionrangetoabout100feet.AFresnellenswillgivethebestpossibleperformance,howeverotherdevicescanbeusedtoextendrange.Althoughthefollowingdevicesmaynotfitthedescriptionofalens,wewillcallthemlensesanyway.ThisdiagramshowsIRexposingbothelementsequallywhennolensisused.ShadowlensSincesimultaneousexposureofbothelementsisthecauseoflimiteddetectionrange,allweneedissomemethodofpreventingtheIRfromexposingbothelementssimultaneouslyastheIRemittingbodymovesacrossthefrontofthesensor,evenatgreaterdistancesfromthesensor.Thesensorelementsare0.039inch(1mm)wideandarespaced0.039inch(1mm)apart.IfweplaceathinverticalstripofIRopaquematerialabout0.060inch(1.5mm)widecenteredinfrontofthesensorwecanpreventsomeoftheIRfromstrikingthesurfaceofthesensorbyproducingashadow,eveniftheIRemittingbodyisatagreaterdistancefromthesensor.ThefollowingfigureshowssuchabafflebutinthisexampletheIRstillexposesbothelementsequally.word文檔精品文檔分享Byplacingabaffleormaskinfrontofthesensor,wecanblocksomeoftheIRandproduceashadowonthesensorThisnextfigureshowswhathappenswhentheIRemittingbodymovesacrossthefrontofthesensorevenatgreaterdistances.Thebaffleallowsfullexposureofelement1whileblockingtheIRsoitproducesashadowoverelement2anddoesnotexposeit.Thissimplelensextendsdetectionrangeupto20feetandiseasilymadefromastripofpaperorothermaterial.Thebafflecanbespaced1/2inch(12mm)to1inch(25mm)infrontofthesensor.Thegreaterspacinggivesanarrowerdetectionangle.AstheIRsourcemoves,thebaffleblocksitfromexposingoneofthesensorelementswhilefullyexposingtheword文檔精品文檔分享other.Thissameideacanbeexpandedtoproduceawideanglelens.MultiplebafflestripscanbeplacedinfrontofthesensortoalternatelyblockIRfromonesensorelementatatimeevenwhentheIRemittingbodyisatgreateranglestothefrontofthesensor.Thismultiplebaffleshadowlensprovidesawidedetectionangle.Thelensshouldbecurvedsoallbafflesarethesamedistancefromthefrontofthesensor.PinholelensAnothersimplefocusingdevicethatwillexposeonePIRsensorelementatatimecanbemadeusingathinpieceofIRopaquematerialwithaholeinitthatwillfunctionasapinholelenssimilartothelensofapinholecamera.Thefunctionofapinholecameralensisdescribedin://science.howstuffworks/question131.htm.ThelensholeinacameraisusuallysmallbutcanbemuchlargerinasensorapplicationwhereimagedetailisnotnecessaryandonlytheIRradiationfromtheanimalmustbefocusedontoonesensingelementatatime.IRinthe5~15micrometerwavelengthrangewillnotpassthroughmostmaterialssoyoucanmakealensofpaper,plasticormetalfoil.Theholeshouldbeaboutinch(6.4mm)diameter.word文檔精品文檔分享Lensspacingisnotcriticalbutitshouldbeaboutinch(12mm)to1inch(25mm)fromthefrontofthesensor.Adetectionrangeofupto20feetcanbeobtainedwiththistypeoflens.Althoughanarrowfieldofviewisusuallymostdesirableforanimalphotos,awidefieldofviewcanbeobtainedbyplacingseveralholesinthelensmaterialandcurvingthelensinfrontofthesensorsoallholesareanequaldistancefromthefrontofthesensor.Anothertypeoflenscanbemadebyplacingatubeab