人體熱釋電紅外傳感器PIR原理

1、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(cè)器領(lǐng)域中， 被動(dòng)式熱釋電紅外探測(cè)器的應(yīng)用非常廣泛， 因其價(jià)格低廉、 技術(shù)性能穩(wěn)定而受到廣大用戶和專業(yè)人士的歡迎。被動(dòng)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(huì)發(fā)生特定波長(zhǎng) 10 以 m 左右的紅外線， 被動(dòng)式紅外探頭就是靠探測(cè)人體發(fā)射的10 以 m&右的紅外線而進(jìn)行工作的。人體發(fā)射的 10pm 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(shí)就會(huì)失去電荷平衡， 向外釋放電荷， 后續(xù)電路經(jīng)檢測(cè)處理后就能產(chǎn)生報(bào)

2、警信號(hào)。(1)這種探頭是以探測(cè)人體輻射為目標(biāo)的。所以熱釋電元件對(duì)波長(zhǎng)為 10pm 左右的紅外輻射必須非常敏感。(2)為了僅僅對(duì)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(dòng)紅外探頭，具傳感器包含兩個(gè)互相串聯(lián)或并聯(lián)的熱釋電元。 而且制成的兩個(gè)電極化方向正好相反， 環(huán)境背景輻射對(duì)兩個(gè)熱釋元件幾乎具有相同的作用， 使其產(chǎn)生釋電效應(yīng)相互抵消， 于是探測(cè)器無信號(hào)輸由。(4)一旦人侵入探測(cè)區(qū)域內(nèi)，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(hào)處理而報(bào)警。(5)菲涅爾濾光片根據(jù)性能要求

3、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(chǎng)，視場(chǎng)越多，控制越嚴(yán)密。被動(dòng)式熱釋電紅外探頭的優(yōu)缺點(diǎn)：優(yōu)點(diǎn)：本身不發(fā)任何類型的輻射，器件功耗很小，隱蔽性好。價(jià)格低廉。缺點(diǎn)：容易受各種熱源、光源干擾被動(dòng)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。易受射頻輻射的干擾。環(huán)境溫度和人體溫度接近時(shí)，探測(cè)和靈敏度明顯下降，有時(shí)造成短時(shí)失靈。抗干擾性能：1,防小動(dòng)物干擾探測(cè)器安裝在推薦地使用高度，對(duì)探測(cè)范圍內(nèi)地面上地小動(dòng)物，一般不產(chǎn)生報(bào)警。2,抗電磁干擾探測(cè)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(huì)引起誤報(bào)。3.抗燈光干擾探測(cè)器在正常靈敏度的范圍

4、內(nèi)，受 3 米外 H4 鹵素?zé)敉高^玻璃照射，不產(chǎn)生報(bào)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(bào)率與安裝的位置和方式有極大的關(guān)系，正確的安裝應(yīng)滿足下列條1.紅外線熱釋電傳感器應(yīng)離地面 2.0-2.2 米。2 .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。3 .紅外線熱釋電傳感器探測(cè)范圍內(nèi)不得隔屏、家具、大型盆景或其他隔離物。4 .紅外線熱釋電傳感器不要直對(duì)窗口，否則窗外的熱氣流擾動(dòng)和人員走動(dòng)會(huì)引起誤報(bào)， 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(dòng)的地方。紅外線熱釋電傳感器對(duì)人體的敏感程度還和人的運(yùn)動(dòng)方向關(guān)系很大。

5、熱釋電紅外傳感器對(duì)于徑向移動(dòng)反應(yīng)最不敏感， 而對(duì)于橫切方向（即與半徑垂直的方向）移動(dòng)則最為敏感,在現(xiàn)場(chǎng)選擇合適的安裝位置是避免紅外探頭誤報(bào)、 求得最佳檢測(cè)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燒材料注壓而成的薄片，鏡片表面一面為光面， 另一面刻錄了由小到大的同心圓。 菲涅爾透鏡的在很多時(shí)候相當(dāng)于紅外線及可見光的凸透鏡， 效果較好， 但成本比普通的凸透鏡低很多。 菲涅爾透鏡可按照光學(xué)設(shè)計(jì)或結(jié)構(gòu)進(jìn)行分類。 菲涅爾透鏡作用有兩個(gè)：一是聚焦作用；二是將探測(cè)區(qū)域內(nèi)分為若干個(gè)明區(qū)和暗區(qū)，使進(jìn)入探測(cè)區(qū)域的移動(dòng)物體能以溫度變化的形式在 PIR （被動(dòng)紅外線探測(cè)器）上產(chǎn)生變化熱釋紅外

6、信號(hào)。2.2作用菲涅爾透鏡利用透鏡的特殊光學(xué)原理， 在探測(cè)器前方產(chǎn)生一個(gè)交替變化的“盲區(qū)”和“高靈敏區(qū)”， 以提高它的探測(cè)接收靈敏度。 當(dāng)有人從透鏡前走過時(shí)，人體發(fā)生的紅外線就不斷地交替從“盲區(qū)”進(jìn)入“高靈敏區(qū)”， 這樣就使接收到的紅外信號(hào)以忽強(qiáng)忽弱的脈沖形式輸入，從而強(qiáng)其能量幅度。菲涅爾透鏡菲涅爾透鏡， 簡(jiǎn)單的說就是在透鏡的一側(cè)有等距的齒紋， 通過這些齒紋，可以達(dá)到對(duì)指定光譜范圍的光帶通（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(jià)昂貴。菲涅爾透鏡可以極大的降低成本。典型的例子就是 PIRoPIR 廣泛的用在警報(bào)器上。如果你拿一個(gè)看看，你會(huì)發(fā)現(xiàn)在每個(gè) PIR 上都有個(gè)塑料的小帽

7、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涉濾光鏡的光聚焦在硅光電二級(jí)探測(cè)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(shí)可先用蒸儲(chǔ)水或普通凈水沖洗，再用脫脂棉擦拭。3.HowInfraredmotiondetectorcomponentsworkInfraredRadiationInfraredradiationexistsintheelectromagneticspectrumatawavelengththatislongerthanvisiblelight

8、.Itcannotbeseenbutitcanbedetected.Objectsthatgenerateheatalsogenerateinfraredradiationandthoseobjectsincludeanimalsandthehumanbodywhoseradiationisstrongestatawavelengthof9.4um.Infraredinthisrangewillnotpassthroughmanytypesofmaterialthatpassvisiblelightsuchasordinarywindowglassandplastic.Howeveritwil

9、lpassthrough,withsomeattenuation,materialthatisopaquetovisiblelightsuchasgermaniumandsilicon.AnunprocessedsiliconwafermakesagoodIRwindowinaweatherproofenclosureforoutdooruse.Italsoprovidesadditionalfilteringforlightinthevisiblerange.9.4uminfraredwillalsopassthroughpolyethylenewhichisusuallyusedtomak

10、eFresnellensestofocustheinfararedontosensorelements.PyroelectricSensorsThepyroelectricsensorismadeofacrystallinematerialthatgeneratesasurfaceelectricchargewhenexposedtoheatintheformofinfraredradiation.Whentheamountofradiationstrikingthecrystalchanges,theamountofchargealsochangesandcanthenbemeasuredw

11、ithasensitiveFETdevicebuiltintothesensor.ThesensorelementsaresensitivetoradiationoverawiderangesoafilterwindowisaddedtotheTO5packagetolimitdetectableradiationtothe8to14mmrangewhichismostsensitivetohumanbodyradiation.Typically,theFETsourceterminalpin2connectsthroughapulldownresistorofabout100Ktogroun

12、dandfeedsintoatwostageamplifierhavingsignalconditioningcircuits.Theamplifieristypicallybandwidthlimitedtobelow10Hztorejecthighfrequencynoiseandisfollowedbyawindowcomparatorthatrespondstoboththepositiveandnegativetransitionsofthesensoroutputsignal.Awellfilteredpowersourceoffrom3to15voltsshouldbeconne

13、ctedtotheFETdrainterminalpin1.ThePIR325sensorhastwosensingelementsconnectedinavoltagebuckingconfiguration.Thisarrangementcancelssignalscausedbyvibration,temperaturechangesandsunlight.Abodypassinginfrontofthesensorwillactivatefirstoneandthentheotherelementwhereasothersourceswillaffectbothelementssimu

14、ltaneouslyandbecancelled.TheradiationsourceFRESNELLENSTHERMALENERGYTYPICALCONFIGURATIONmustpassacrossthesensorinahorizontaldirectionwhensensorpins1and2areonahorizontalplanesothattheelementsaresequentiallyexposedtotheIRsource.AfocusingdeviceisusuallyusedinfrontofthesensorThefigurebelowshowsthePIR325e

15、lectricalspecificationsandlayoutinitsTO5package.Notethewideviewinganglewithoutanexternallens.infraredsourcemovementPIR325SENSITIVEAREA2ELEMENTSSPECTRALRESPONSE1411mOUTPUTVOLTAGEmvpp20NOISEuVpp20OFFSETVOLTAGEvolts1.0SUPPLYVOLTAGEvolts2,5-15OPERATINGTEMPc30-70TestConditionsforoutputvoltage:Supplyvolta

16、ge=5volts100Kloadresistorfrompin2to3IRsource=Handmoving6fromsensorThisisatypicalapplicationcircuitthatdrivesarelay.R10andC6adjusttheamountoftimethatRY1remainsenergizedaftermotionisdetected.DownloadPDFdrawing.BOTTOMVIEWFresnelLensAFresnellens(pronouncedFrennel)isaPlanoConvexlensthathasbeencollapsedon

17、itselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchsmallerinthicknessandthereforehaslessabsorptionlosses.FRESNELOurFL65FresnellensismadeofaninfraredtransmittingmaterialthathasanIRtransmissionrangeof8to14umwhichismostsensitivetohumanbodyradiation.ItisdesignedtohaveitsgroovesfacingIC1=L

18、M324ICZ=CW5MPIR=PIR325D1-D5=1N914R10KjohmsXCBmid=ONlimsRY1-coilvoHagerating=V+voflag0MOTIONDETECTORPLAMOCONVEXtheIRsensingelementsothatasmoothsurfaceispresentedtothesubjectsideofthelenswhichisusuallytheoutsideofanenclosurethathousesthesensor.Thelenselementisroundwithadiameterof1inchandhasaflangethat

19、is1.5inchessquare.Thisflangeisusedformountingthelensinasuitableframeorenclosure.MountingcanbestandmosteasilybedonewithstripsofScotchtape.Siliconerubbercanalsobeusedifitoverlapstheedgestoformacaptivemount.TheFL65hasafocallengthof0.65inchesfromthelenstothesensingelement.Ithasbeendeterminedbyexperiment

20、tohaveafieldofviewofapproximately10degreeswhenusedwithaPIR325Pyroelectricsensor.ThisrelativelyinexpensiveandeasyPyroelectricSensorandFresnelLenscanbeusedinavarietyofscienceprojects,robotsandotherusefuldevices.3.1FocusingdevicesforpyroelectricsensorsA.1PyroelectricinfraredsensorsA.2Firstwewilllookata

21、pyroelectricinfraredIRFRESNELLENSinstalllenswithgroovesfacingPIRfocallength_0,65_0.015thicknessOptimumtransmittanceinthe8to14urnregiontouseinfraredsensorandseehowitismadeandwhyafocusingdeviceisnecessary.Acommonlyusedpyroelectricinfraredsensorhastwosensingelementsinternallyconnectedinavoltagebuckingc

22、onfiguration.ApyroelectricsensorhasaninfraredfilterwindowthatadmitsIRwithinthe5to15micrometerwavelengthrange.Oneendofthetwoseries-connectedelementsinananalogsensorisconnectedtopin3thatisnormallygrounded.TheotherendconnectsinternallytothegateofaFieldEffectTransistorandtoaveryhighvaluepulldownresistor

23、.PowerisappliedtoFETPIRdrainpin1andtheoutputsignalcomesfromFEIsourcepin2whichusuallyconnectsthroughanexternalpulldownresistortogroundandtoanamplifier.Adigitalsensornotshownhere,includesinternalprocessingcircuitsandoutputsdigitalpulses.A.3ThesensorishousedinaTO5typepackage.Sensingelementsareeach0.039

24、inch(1mm)wideandarespaced0.039inch(1mm)apart.A.4Environmentalconditionssuchastemperaturechangesandsunlightwillaffectbothelementssimultaneouslyandwillproducethesameamountofoutputfromeachelementbutofopposingpolarityandwillthereforebecancelled.Thesensorwillonlyproduceachangeinitsoutputvoltagewhenoneofi

25、tselementsisexposedtoachangeinradiationandtheotherisnotexposed.AnIRemittingbodymovingacrossthefrontofasensorwillexposefirstone,thenbothandthentheothersensorEHvl&ixelement.Theoutputsignalwaveformfromananalogsensorshowsthatformotioninonedirection,firstapositive,thenzeroandthenanegativetransitionre

26、sults.Motionintheotherdirectionwillproducefirstanegative,thenzeroandthenapositivetransition.WhenalensisnotusedinfrontofasensorandanIRemittingbodyisclosetothesensor,aboutA.53or4feetanditmovesacrossthefrontofthesensor,theradiatedIRwillexposeoneelementmorethantheotherandavoltageoutputwillresult.However

27、,whentheIRemittingbodyisfurtherawayfromthesensoritsradiationpatternbecomesblurredandbothelementsareexposedmoreequally,resultinginnovoltageoutput.Thelimiteddetectionrangeisduetoalackofunequalexposure.Placingalensinfrontofthesensorextendsitsdetectionrange.A.6TheFresnellensA.7AFresnellensisaPlanoConvex

28、lensthathasbeencollapsedonitselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchthinnerandthereforehaslessabsorptionloss.AFresnellensisusuallythinandflexibleandisabout0.015inch(0.38mm)thickwithgroovesmoldedintoonesurface.n.r?joror.VFKThegroovesideofthelensusuallyfacesthePIRsensor.AFresne

29、llensbothcapturesmoreIRradiationandfocusesittoasmallpoint.ThisfocalpointmovesacrossthesensorastheIRsourcemovesandexposesoneelement065FRESNELg-lens廿曲LEMSgroowsf&cinqPRatatime.AFresnellenscanextenddetectionrangetoabout100feet.AFresnellenswillgivethebestpossibleperformance,howeverotherdevicescanbeu

30、sedtoextendrange.Althoughthefollowingdevicesmaynotfitthedescriptionofalens,wewillcallthemlensesanyway.ThisdiagramshowsIRexposingbothelementsequallywhennolensisused.ShadowlensSincesimultaneousexposureofbothelementsisthecauseoflimiteddetectionrange,allweneedissomemethodofpreventingtheIRfromexposingbot

31、helementssimultaneouslyastheIRemittingbodymovesacrossthefrontofthesensor,evenatgreaterdistancesfromtheTO=If/JLAZIIC.O：9inFnwmADEfchDSPACEDQ-.N口imn)sensor.Thesensorelementsare0.039inch(1mm)wideandarespaced0.039inch(1mm)apart.IfweplaceathinverticalstripofIRopaquematerialabout0.060inch(1.5mm)widecenteredinfrontofthesensorwecanpreventsomeoftheIRfromstrikingthesurfaceofthesensorbyproducingashadow,eveniftheIRemittingbodyisatagreaterdistancefromthesensor.ThefollowingfigureshowssuchabafflebutinthisexampletheIRstillexposesbothelementsequally.Byplacingabaffleormaskinfrontoft