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10pm左右的紅外線，被動式紅外探頭就是靠探測人體發(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。這種探頭是以探測人體輻射為目標(biāo)的。所以熱釋

2、電元件對波長為10pm左右的紅外輻射必須非常敏感。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。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(yīng)相互抵消，于是探測器無信號輸出。一旦人侵入探測區(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)信號處理而報警。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，視場越多，控制越嚴(yán)密。被動式熱釋電紅外

3、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。易受射頻輻射的干擾。環(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，對探測范圍內(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?？篃艄飧蓴_探測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窗口，否則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動方向關(guān)系很大。熱釋電紅外傳感器對于徑向移動反應(yīng)最不敏感，而對于橫切方向（即與半徑垂直的方向）移動則最為敏感在現(xiàn)場選擇合適的安裝位置是避免紅外探頭誤報、求得最佳檢測靈敏

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)計或結(jié)構(gòu)進(jìn)行分類。菲涅爾透鏡作用有兩個：一是聚焦作用；二是將探測區(qū)域內(nèi)分為若干個明區(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“盲區(qū)”和“高靈敏區(qū)”，以提高它的探測接收靈敏度。當(dāng)有人從透鏡前走過時，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涉濾光鏡的光聚焦在硅光電二級探測器的光敏

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