人體熱釋電紅外傳感器PIR原理解析

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)出特定波長10pm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10pm左右的紅外線而進(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)警信號(hào)。這種探頭是以探測(cè)人體輻射為目標(biāo)的。所以熱釋

2、電元件對(duì)波長為10pm左右的紅外輻射必須非常敏感。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。被動(dòng)紅外探頭，其傳感器包含兩個(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)輸出。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。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(chǎng)，視場(chǎng)越多，控制越嚴(yán)密。被動(dòng)式熱釋電紅外

3、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：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?？闺姶鸥蓴_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)?？篃艄飧蓴_探測(cè)器在正常靈敏度的范圍內(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)，

4、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(cè)范圍內(nèi)不得隔屏、家具、大型盆景或其他隔離物。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。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

5、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)出的紅外線就不斷

6、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PIR。PIR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

7、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)可先用蒸餾水或普通凈水沖洗，再用脫脂棉擦拭。3.HowInfraredmotiondetectorcomponentsworkInfraredRadiationInfraredradiationexistsintheelectromagneticspectrumatawavelengththatisIongerthanvisiblelight.Itcannotbeseenbutitcanbedetected.Objectsthatgenerateheatalsogenerateinfraredradiationandthoseobjec

8、tsincludeanimalsandthehumanbodywhoseradiationisstrongestatawavelengthof9.4um.Infraredinthisrangewillnotpassthroughmanytypesofmaterialthatpassvisiblelightsuchasordinarywindowglassandplastic.Howeveritwillpassthrough,withsomeattenuation,materialthatisopaquetovisiblelightsuchasgermaniumandsilicon.Anunpr

9、ocessedsiliconwafermakesagoodIRwindowinaweatherproofenclosureforoutdooruse.Italsoprovidesadditionalfilteringforlightinthevisiblerange.9.4uminfraredwillalsopassthroughpolyethylenewhichisusuallyusedtomakeFresnellensestofocustheinfararedontosensorelements.PyroelectricSensors.Thepyroelectricsensorismade

10、ofacrystallinematerialthatgeneratesasurfaceelectricchargewhenexposedtoheatintheformofinfraredradiation.Whentheamountofradiationstrikingthecrystalchanges,theamountofchargealsochangesandcanthenbemeasuredwithasensitiveFETdevicebuiltintothesensor.Thesensorelementsaresensitivetoradiationoverawiderangesoa

11、filterwindowisaddedtotheTO5packagetolimitdetectableradiationtothe8to14mmrangewhichismostsensitivetohumanbodyradiation.Typically,theFETsourceterminalpin2connectsthroughapulldownresistorofabout100Ktogroundandfeedsintoatwostageamplifierhavingsignalconditioningcircuits.Theamplifieristypicallybandwidthli

12、mitedtobelow10Hztorejecthighfrequencynoiseandisfollowedbyawindowcomparatorthatrespondstoboththepositiveandnegativetransitionsofthesensoroutputsignal.Awellfilteredpowersourceoffrom3to15voltsshouldbeconnectedtotheFETdrainterminalpin1.TVPICALCONFIGURATIONAMPLIFIERCOMPARATOROUTPUTQThePIR325sensorhastwos

13、ensingelementsconnectedinavoltagebuckingconfiguration.Thisarrangementcancelssignalscausedbyvibration,temperaturechangesandsunlight.Abodypassinginfrontofthesensorwillactivatefirstoneandthentheotherelementwhereasothersourceswillaffectbothelementssimultaneouslyandbecancelled.Theradiationsourcemustpassa

14、crossthesensorinahorizontaldirectionwhensensorpins1and2areonahorizontalplanesothattheelementsaresequentiallyexposedtotheIRsource.AfocusingdeviceisusuallyusedinfrontofthesensordetectingareainfraredsourcemovementThefigurebelowshowsthePIR325electricalspecificationsandlayoutinitsTO5package.Notethewidevi

15、ewinganglewithoutanexternallens.BOTTOMVIEWPIR325SENSITIVEAREA2ELEMENTSSPECTRALRESPONSE5-14umOUTPUTVOLTAGEmvpp20NOISEuVpp20OFFSETVOLTAGEvolts1.0SUPPLYVOLTAGEvolts2.5-15OPERATINGTEMPc30-70TestConditionsforoutputvoltage:Supplyvoltage=5volts100Kloadresistorfromp州2to3IRsource=Handmoving6fromsensorViewAng

16、leThisisatypicalapplicationcircuitthatdrivesarelay.R10andC6adjusttheamountoftimethatRY1remainsenergizedaftermotionisdetected.DownloadPDFdrawing.O+-412VOLTSIC1=LM3Z4IC2七D4器EF1K=PIR3Z5K10KipnisXCfinM=ONlinemsDi-IDS=1N91IRV1-coilruling口V*vottageMOTIONDETECTORFresnelLensAFresnellens(pronouncedFrennel)is

17、aPlanoConvexlensthathasbeencollapsedonitselftoformaflatlensthatretainsitsopticalcharacteristicsbutismuchsmallerinthicknessandthereforehaslessabsorptionlosses.FRESNELOurFL65FresnellensismadeofaninfraredtransmittingmaterialthathasanIRtransmissionrangeof8to14umwhichismostsensitivetohumanbodyradiation.I

18、tisdesignedtohaveitsgroovesfacingtheIRsensingelementsothatasmoothsurfaceispresentedtothesubjectsideofthelenswhichisusuallytheoutsideofanenclosurethathousesthesensor.Thelenselementisroundwithadiameterof1inchandhasaflangethatis1.5inchessquare.Thisflangeisusedformountingthelensinasuitableframeorenclosu

19、re.MountingcanbestandmosteasilybedonewithstripsofScotchtape.Siliconerubbercanalsobeusedifitoverlapstheedgestoformacaptivemount.TheFL65hasafocallengthof0.65inchesfromthelenstothesensingelement.Ithasbeendeterminedbyexperimenttohaveafieldofviewofapproximately10degreeswhenusedwithaPIR325Pyroelectricsens

20、or.focallength0.G5-i.iLinstalllenswithLENSgroovesfatingPIR1.6mountingborderactivearea0015thickneOptimumtransmittanceinthe8to14urnregionThisrelativelyinexpensiveandeasytousePyroelectricSensorandFresnelLenscanbeusedinavarietyofscieneeprojects,robotsandotherusefuldevices.3.1Focusingdevicesforpyroelectr

21、icinfraredsensorsA.1PyroelectricinfraredsensorsA.2Firstwewilllookatapyroelectricinfraredsensorandseehowitismadeandwhyafocusingdeviceisnecessary.Acommonlyusedpyroelectricinfraredsensorhastwosensingelementsinternallyconnectedinavoltagebuckingconfiguration.PIRApyroelectricsensorhasaninfraredfilterwindo

22、wthatadmitsIRwithinthe5to15micrometerwavelengthrange.Oneendofthetwoseries-connectedelementsinananalogsensorisconnectedtopin3thatisnormallygrounded.TheotherendconnectsinternallytothegateofaFieldEffectTransistorandtoaveryhighvaluepulldownresistor.PowerisappliedtoFETdrainpin1andtheoutputsignalcomesfrom

23、FETsourcepin2whichusuallyconnectsthroughanexternalpulldownresistortogroundandtoanamplifier.Adigitalsensornotshownhere,ineludesinternalprocessingcircuitsandoutputsdigitalpulses.A.3ThesensorishousedinaTO5typepackage.Sensingelementsareeach0.039inch(1mm)wideandarespaced0.039inch(1mm)apart.aOTHklVIEnVA.4

24、Environmentalconditionssuchastemperaturechangesandsunlightwillaffectbothelementssimultaneouslyandwillproducethesameamountofoutputfromeachelementbutofopposingpolarityandwillthereforebecancelled.Thesensorwillonlyproduceachangeinitsoutputvoltagewhenoneofitselementsisexposedtoachangeinradiationandtheoth

25、erisnotexposed.negative,thenzeroandthenapositivetransition.A.5WhenalensisnotusedinfrontofasensorandanIRemittingbodyisclosetothesensor,about3or4feetanditmovesacrossthefrontofthesensor,theradiatedIRwillexposeoneelementmorethantheotherandavoltageoutputwillresult.However,whentheIRemittingbodyisfurtheraw

26、ayfromthesensoritsradiationpatternbecomesblurredandbothelementsareexposedmoreequally,resultinginnovoltageoutput.Thelimiteddetectionrangeisduetoalackofunequalexposure.Placingalensinfrontofthesensorextendsitsdetectionrange.A.6TheFresnellensA.7AFresnellensisaPlanoConvexlensthathasbeencollapsedonitselft

27、oformaflatlensthatretainsitsopticalcharacteristicsbutismuchthinnerandthereforehaslessabsorptionloss.detectionrangetoabout100feet.AFresnellenswillgivethebestpossibleperformanee,howeverotherdevicescanbeusedtoextendrange.Althoughthefollowingdevicesmaynotfitthedescriptionofalens,wewillcallthemlensesanyw

28、ay.ShadowlensSincesimultaneousexposureofbothelementsisthecauseoflimiteddetectionrange,allweneedissomemethodofpreventingtheIRfromexposingbothelementssimultaneouslyastheIRemittingbodymovesacrossthefrontofthesensor,evenatgreaterdistancesfromthesensor.Thesensorelementsare0.039inch(1mm)wideandarespaced0.

29、039inch(1mm)apart.IfweplaceathinverticalstripofIRopaquematerialabout0.060inch(1.5mm)widecenteredinfrontofthesensorwecanpreventsomeoftheIRfromstrikingthesurfaceofthesensorbyproducingashadow,eveniftheIRemittingbodyisatagreaterdistancefromthesensor.ThefollowingfigureshowssuchabafflebutinthisexampletheI

30、Rstillexposesbothelementsequally.ThisnextfigureshowswhathappenswhentheIRemittingbodymovesacrossthefrontofthesensorevenatgreaterdistances.Thebaffleallowsfullexposureofelement1whileblockingtheIRsoitproducesashadowoverelement2anddoesnotexposeit.Thissimplelensextendsdetectionrangeupto20feetandiseasilyma

31、defromastripofpaperorothermaterial.Thebafflecanbespaced1/2inch(12mm)to1inch(25mm)infrontofthesensor.Thegreaterspacinggivesanarrowerdetectionangle.other.Thissameideacanbeexpandedtoproduceawideanglelens.MultiplebafflestripscanbeplacedinfrontofthesensortoalternatelyblockIRfromonesensorelementatatimeeve

32、nwhentheIRemittingbodyisatgreateranglestothefrontofthesensor.PinholelensAnothersimplefocusingdevicethatwillexposeonePIRsensorelementatatimecanbemadeusingathinpieceofIRopaquematerialwithaholeinitthatwillfunctionasapinholelenssimilartothelensofapinholecamera.Thefunctionofapinholecameralensisdescribedi

33、nhttp:/science.howstuffworkscom/question131htm.ThelensholeinacameraisusuallysmallbutcanbemuchlargerinasensorapplicationwhereimagedetailisnotnecessaryandonlytheIRradiationfromtheanimalmustbefocusedontoonesensingelementatatime.IRinthe515micrometerwavelengthrangewillnotpassthroughmostmaterialssoyoucanm

34、akealensofpaper,plasticormetalfoil.Theholeshouldbeaboutinch(6.4mm)diameter.Lensspacingisnotcriticalbutitshouldbeaboutinch(12mm)to1inch(25mm)fromthefrontofthesensor.Adetectionrangeofupto20feetcanbeobtainedwiththistypeoflens.Althoughanarrowfieldofviewisusuallymostdesirableforanimalphotos,awidefieldofviewcanbeobtainedbyplacingseveralholesinthelensmaterialandcurvingthelensinfrontofthesensorsoallholesareanequaldistancefromthefrontofthesensor.Anothertypeoflenscanbemadebyplacingatubeabout3/8inch(10mm)diameterand2inch(50mm)longoverthe