人体热释电红外传感器PIR原理

1、标准实用1. 人体热释电红外传感器PIR原理详解在电子防盗、人体探测器领域中，被动式热释电红外探测器的应用非常广泛，因其价格低廉、 技术性能稳定而受到广大用户和专业人士的欢迎。被动式热释电红外探头的工作原理及特性：人体都有恒定的体温，一般在37度，所以会发出特定波长|l0 m左右的红外线，被动式红外探头就是靠探测人体发射的10 m左右的红外线而进行工作的。人体发射的|l0 m左右的红外线通过菲涅尔滤光片增强后聚集到红外感应源上。红外感应 源通常采用热释电元件，这种元件在接收到人体红外辐射温度发生变化时就会失去电荷平衡，向外释放电荷，后续电路经检测处理后就能产生报警信号。(1) 这种探头是以探测

2、人体辐射为目标的。所以热释电元件对波长为 10 pm左右的红外辐射必须非常敏感。(2) 为了仅仅对红外辐射敏感，在它的辐射照面通常覆盖有特殊的菲涅尔滤光片，使环 境的干扰受到明显的控制作用。(3) 被动红外探头，其传感器包含两个互相串联或并联的热释电元。而且制成的两个电极化方向正好相反，环境背景辐射对两个热释元件几乎具有相同的作用，使其产生释电效应相互抵消，于是探测器无信号输出。(4) 一旦人侵入探测区域内，人体红外辐射通过部分镜面聚焦，并被热释电元接收，但是两片热释电元接收到的热量不同，热释电也不同，不能抵消，经信号处理而报警。(5) 菲涅尔滤光片根据性能要求不同，具有不同的焦距(感应距离)

3、，从而产生不同的监控视场，视场越多，控制越严密。被动式热释电红外探头的优缺点：优点：本身不发任何类型的辐射，器件功耗很小，隐蔽性好。价格低廉。缺点：容易受各种热源、光源干扰被动红外穿透力差，人体的红外辐射容易被遮挡，不易被探头接收。易受射频辐射的干扰。环境温度和人体温度接近时，探测和灵敏度明显下降，有时造成短时失灵。抗干扰性能：1. 防小动物干扰探测器安装在推荐地使用高度，对探测范围内地面上地小动物，一般不产生报警。2. 抗电磁干扰探测器的抗电磁波干扰性能符合GB10408中461要求，一般手机电磁干扰不会引起误报。3. 抗灯光干扰探测器在正常灵敏度的范围内，受3米外H4卤素灯透过玻璃照射，不

4、产生报警。红外线热释电传感器 的安装要求：红外线热释电人体传感器只能安装在室内，其误报率与安装的位置和方式有极大的关 系，正确的安装应满足下列条件：1. 红外线热释电传感器应离地面2.0-2.2米。2. 红外线热释电传感器远离空调 ，冰箱，火炉等空气温度变化敏感的地方。3. 红外线热释电传感器探测范围内不得隔屏、家具、大型盆景或其他隔离物。4. 红外线热释电传感器不要直对窗口，否则窗外的热气流扰动和人员走动会引起误报，有条件的最好把窗帘拉上。红外线热释电传感器也不要安装在有强气流活动的地方。红外线热释电传感器对人体的敏感程度还和人的运动方向关系很大。热释电红外传感器对于径向移动反应最不敏感 ，

5、而对于横切方向 （即与半径垂直的方向）移动则最为敏感在 现场选择合适的安装位置是避免红外探头误报、求得最佳检测灵敏度极为重要的一环。2. 菲涅尔透镜2.1概述菲涅尔透镜多是由聚烯烃材料注压而成的薄片,镜片表面一面为光面,另一面刻录了由小到文案大全效果较好，但成本菲涅尔透镜作用有两大的同心圆。菲涅尔透镜的在很多时候相当于红外线及可见光的凸透镜, 比普通的凸透镜低很多。 菲涅尔透镜可按照光学设计或结构进行分类。个：一是聚焦作用；二是将探测区域内分为若干个明区和暗区，使进入探测区域的移动物体 能以温度变化的形式在 PIR （被动红外线探测器）上产生变化热释红外信号。2.2 作用菲涅尔透镜利用透镜的特

6、殊光学原理，在探测器前方产生一个交替变化的“盲区”和“高灵敏区”，以提高它的探测接收灵敏度。当有人从透镜前走过时，人体发出的红外线就不断地 交替从“盲区”进入“高灵敏区”，这样就使接收到的红外信号以忽强忽弱的脉冲形式输入,从而强其能量幅度。菲涅尔透镜菲涅尔透镜，简单的说就是在透镜的一侧有等距的齿纹，通过这些齿纹，可以达到对指定光谱范围的光带通（反射或者折射）的作用。传统的打磨光学器材的带通光学滤镜造价昂贵。菲 涅尔透镜可以极大的降低成本。典型的例子就是 PIR。PIR广泛的用在警报器上。如果你拿一个看看，你会发现在每个PIR上都有个塑料的小帽子。 这就是菲涅尔透镜。 小帽子的内部都刻上了齿纹。

7、这种菲涅尔透镜可以将入射光的频率峰值限制到10微米左右（人体红外线辐射的峰值）。菲涅耳透镜可以把透过窄带干涉滤光镜的光聚焦在硅光电二级探测器的光敏面上，菲涅尔透镜不能用任何有机溶液（如酒精等）擦拭，除尘时可先用蒸馏水或普通净水冲洗，再用脱脂棉 擦拭。3. How Infrared motion detector components workInfrared RadiationIn frared radiati onexists in the electromag netic spectrum at a wavele ngth that isIon ger tha n visible ligh

8、t. It cannot be see n but it can be detected. Objects that gen erate heat also gen erate in frared radiatio n and those objects in clude ani malsand the human body whose radiation is strongest at a wavelength of 9.4um.In frared in this range will not pass through many types of material that pass vis

9、iblelight such as ordinary window glass and plastic. However it will pass through, withsome attenuation, material that is opaque to visible light such as germanium andsilicon. An unprocessed silicon wafer makes a good IR window in a weatherproof enclosure for outdoor use. It also provides additional

10、 filtering for light in the visible ran ge. 9.4um in frared will also pass through polyethyle ne which is usually used to make Fres nel le nses to focus the in farared on tosen sor eleme nts.Pyroelectric SensorsThe pyroelectric sen sor is made of a crystall ine material that gen erates a surface ele

11、ctric charge whe n exposed to heat in the form of in frared radiati on. When the amount of radiati on strik ing the crystal cha nges, the amount of charge also cha nges and can the n be measured with a sen sitive FET device built into the sen sor.The sen sor eleme nts are sen sitive to radiati on ov

12、er a wide range so a filter wi ndowis added to the TO5 package to limit detectable radiati on to the 8 to 14mm range which is most sen sitive to huma n body radiati on.Typically, the FET source terminalpin 2 connects through a pulldownresistor ofabout 100 K to ground and feeds into a two stage ampli

13、fierhavingsignalcon diti oning circuits. The amplifier is typically ban dwidth limited to below 10Hz to reject high freque ncy no ise and is followed by a wi ndow comparator that resp onds to both the positive and negativetransitions of the sensor output signal. A wellfiltered power source of from 3

14、 to 15 volts should be conn ected to the FET drain terminal pin 1.The PIR325 sensor has two sensingelementsconnectedin a voltage bucking con figurati on. This arran geme nt can cels sig nals caused by vibrati on, temperature cha nges and sun light. A body pass ing in front of the sen sor will activa

15、te first and then the other element whereas other sources will affect both elementsbe can celled. Thediation source must pass across the sen sor in a horiz on tal direct ion whe n sen sor pins 1 and 2 are on a horiz on tal pla ne so thatfocus ing deviceis usuallythe eleme nts are seque ntially expos

16、ed to the IR source. A used in front of the sen sor、Pyroetecfrtc sensorFresnel fensdetecting areainfrared source movementOUTPUTThe figure below shows the PIR325 electrical specifications and layout in its TO5 package. Note the wide viewing angle without an external lens.This is a typical application

17、 circuit that drives a relay. R10 and C6 adjust the amountof time that RY1 remains energized after motion is detected. DownloadPDFdraw ing.PIFt=PIR325RIQKcMifi X OMDl D5 1N44Ry1 - port vDtage rafeng 誉 W vcmsgeMOTION DETECTORFresnel LensA Fres nel le ns (pronounced Frenn el) is a Plano Convex lens th

18、at has bee n collapsed on itself to form a flat lens that retains its optical characteristics but is much smaller in thick ness and therefore has less absorpti on losses.or10Our FL65 Fresnel lens is made of an infrared transmitting material that has an IR tran smissi on range of 8 to 14um which is m

19、ost sen sitive to huma n body radiati on. It is desig ned to have its grooves facing the IR sensing eleme nt so that a smooth surface is prese nted to the subject side of the lens which is usually the outside of an en closure that houses the sen sor.The lens eleme nt is round with a diameter of 1 in

20、ch and has a flange that is 1.5inches square. This flange is used for mountingthe lens in a suitable frameenclosure. Mounting can best and most easily be done with strips of Scotch tape.Silicone rubber can also be used if it overlaps the edges to form a captive mount.The FL65 has a focal le ngth of

21、0.65 in ches from the lens to the sensing eleme nt. Ithas been determined by experiment to have a field of view of approximately degrees whe n used with a PIR325 Pyroelectric sen sor.This relatively in expe nsive and easy to use Pyroelectric Sen sor and Fres nel Lens can be used in a variety of scie

22、 nee projects, robots and other useful devices.3.1 Focus ing devices for pyroelectric in frared sen sorsA.1 Pyroelectric in frared sen sorsA.2 First we will look at a pyroelectric infrared sensor and see how it is made and why a focus ing device is n ecessary. A com monly used pyroelectric in frared

23、 sen sor has two sensing eleme nts in ternally conn ected in a voltage buck ing con figurati on.A pyroelectric sensor has an in frared filter win dow that admits IR within the 5 to 15 micrometer wavele ngth ran ge. One end of the two series-c onn ecte d eleme nts in an an alog sen sor is conn ected

24、to pin 3 that is n ormally groun ded. The other end conn ects in ternally to thegate of a Field Effect Tran sistor and to a very high value pulldow n resistor. Power is applied to FET drain pin 1 and the output sig nal comes from FET source pin 2 which usually conn ects through an exter nal pulldow

25、n resistor to ground and to an amplifier. A digital sen sornot show n here, in cludes in ternal process ing circuits and outputs digital pulses.A.3The sen sor is housed in a TO5 type package. Sensing eleme ntsare each 0.039 inch (1mm) wide and are spaced 0.039 inch (1mm)apart.andwillA.4 Environmenta

26、l conditions such as temperature changessun light will affect both eleme nts simulta neously andproduce the same amount of output from each eleme nt but ofoppos ing polarity and will therefore be can celled. The sen sor willonly produce a change in its output voltage when one of itseleme nts is expo

27、sed to a cha nge in radiati on and the other is notexposed.An IR emitti ng body movi ng across the front of a sensor will expose first one, the n both and the n the other sensor eleme nt.The output sig nal wavefor m from an an alog sensor shows that for moti on in one directi on ,first a positive, t

28、he n zero and the n a n egative tran sitio n results.Motion in the other directi on will produce first a n egative, the n zero and the n a positive tran sitio n.A.5 Whe n a lens is not used in front of a sen sor and an IR emitt ingbody is close to the sensor, about 3 or 4 feet and it moves acrossthe

29、 front of the sensor, the radiated IR will expose one elementmore than the other and a voltage output will result. However, when the IR emitting body is further away from the sensor its radiati on pattern becomes blurred and both eleme nts areexposed more equally, resulting in no voltage output. The

30、 limiteddetecti on range is due to a lack of un equal exposure. Placi ng alens in front of the sen sor exte nds its detect ion ran ge.A.6 The Fres nel le nsA.7A Fres nel le ns is a Pla no Con vex lens that has bee n collapsed onitself to form a flat lens that retai ns its optical characteristics but

31、is much thinner and therefore has less absorpti on loss.A Fresnel lensisusually thin and flexible andisabout 0.015 inch (0.38mm) thick with grooves molded into onesurface. The groove sideofthelensusually faces the PIR sen sor.AFres nel lens both captures more IR radiatio n and focuses it to a small

32、poi nt.This focal poi nt moves across the sensor as the IR source moves and exposes one eleme nt at a time. A Fres nel lens can exte nd detectio n rangeto about100 feet.A Fresnel lens will give the best possible performanee, however other devices can be used to exte nd ran ge. Although the follow in

33、g devices may not fit the descripti on of a lens, we will call them len ses any way.This diagram shows IR expos in g both eleme nt s equally whe n no lensisused.Shadow lens Si nee simulta neous exposure of both eleme nts is the cause of limited detect ion ran ge, all we n eed is some method of preve

34、 nti ng the IR from expos ing both eleme nts simulta neously as the IR emitti ng body moves across the front of the sen sor, eve n at greater dista nces from the sen sor. The sen sor eleme nts are 0.039 inch (1mm) wide and are spaced 0.039 inch (1mm) apart. If we place a th in vertical strip of IR o

35、paque material about 0.060 inch (1.5mm) wide cen tered in front of the sen sor we can preve nt some of the IR from strik ing the surface of the sen sor by producing a shadow, even if the IR emitting body is at a greater distance from the sensor. The following figure shows such a baffle but in this e

36、xample the IR still exposes both elements equally.By plac ing a baffle or mask in front of the sen sor, we can blocksome of the IR and produc e a shadow on the sensorThis n ext figure shows what happe ns whe n the IR emitt ing body moves across the front of the sen sor eve n at greater dista nces. T

37、he baffle allows full exposure of eleme nt 1 while block ing the IR so it produces a shadow over eleme nt 2 and does not expose it. This simple lens exte nds detect ion range up to 20 feet and is easily made from a strip of paper or other material. The baffle can be spaced 1/2 inch (12mm) to 1 inch

38、(25mm) in front of the sen sor. The greater spaci ng gives a n arrower detect ion an gle.As the IR source moves, the baffle blocks it from expos in g one of the sensor eleme nt s while fully expos in g the other.This same idea can be expa nded to produce a wide an gle lens. Multiple baffle strips ca

39、n be placed in front of the sensor to alternately block IRfrom one sensor element at a time even when the IR emitting body is at greater an gles to the front of the sen sor.This multiple baffle shadow lens provides a wide detectio n an gle. The lens should be curved so all baffles are the same dista

40、 nee from thefront of the sen sor.Pin hole lensAnother simple focusing device that will expose one PIR sensor element at a time can be made using a thin piece of IR opaque material with a hole in it that will function as a pin hole lens similar to the lens of a pi nhole camera.The fun ctio n of a pi

41、n hole camera lens is described in. The lens holein a camera is usually small but can be much larger in a sensor applicati on where image detail is not n ecessary and only the IR radiati on from the ani mal must be focused onto one sensing eleme nt at a time. IR in the 5 15 micrometer wavele ngth ra

42、nge will not pass through most materials so you can make a lens of paper, plastic or metal foil. The hole should be about inch (6.4mm) diameter. Lens spaci ng is not critical but it should be about inch (12mm) to 1 inch (25mm) from the front of the sen sor. A detect ion range of up to 20 feet can be

43、 obta ined with this type of lens.Although a narrow field of view is usually most desirable for animal photos, a wide field of view can be obta ined by placi ng several holes in the lens material and curv ing the lens in front of the sen sor so all holesare an equal dista nee from the front of the sen sor. Ano ther type of lenscan be made by placi ng a tube about 3/8 inch (10mm) diamet