人体热释电红外传感器PIR原理

1、WORD格式 - 可编辑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 10 m左右的红外线，被动式红外探头就是靠探测人体 发射的 10m左右的红外线而进行工作的。 人体发射的 10 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

2、测处理后就能产生报警信号。(1) 这种探头是以探测人体辐射为目标的。所以热释电 元件对波长为 10m 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。(

3、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 ) ，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：WORD格式 - 可编辑容易受各种热源、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 4.

4、6.1 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

5、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 , 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。WORD格式 - 可编辑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，效果较好，但 成本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。菲涅尔透镜

6、作用有两个：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

7、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。这种菲涅尔WORD格式 - 可编辑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 w

8、orkInfrared RadiationInfrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. It cannot be seen but it can be detected. Objects that generate heat also generate infrared radiation and those objects include animals and the human body whose radiation

9、 is strongest at a wavelength of 9.4um. Infrared in this range will not pass through many types of material that pass visible light such as ordinary window glass and plastic. However it will pass through, with some attenuation, material that is opaque to visible light such as germanium and silicon.

10、An unprocessed silicon wafer makes a good IR window in a weatherproof enclosure for outdoor use. It also provides additional filtering for light in the visible range. 9.4um infrared will also pass through polyethylene which is usually used to make Fresnel lenses to focus the infarared ontosensor ele

11、ments.Pyroelectric SensorsThe pyroelectric sensor is made of a crystalline material that generates a surface electric charge when exposed to heat in the form of infrared radiation. WhenWORD格式 - 可编辑the amount of radiation striking the crystal changes,the amount of charge also changes and can then be

12、measured with a sensitive FET device built into the sensor. The sensor elements are sensitive to radiation over a wide range so a filter window is added to the TO5 package to limit detectable radiation to the 8 to 14mm range which is most sensitive to human body radiation.Typically, the FET source t

13、erminal pin 2 connects through a pulldown resistor of about 100 K to ground and feeds intoa two stage amplifier having signalconditioning circuits. The amplifier is typically bandwidth limited to below 10Hz to reject high frequency noise and is followed by a window comparator that responds to both t

14、he positive and negative transitions of the sensor output signal. A well filtered power source of from 3 to 15 volts should be connected to the FET drain terminal pin 1.The PIR325 sensor has two sensing elements connected in a voltage bucking configuration. This arrangement cancels signals caused by

15、 vibration, temperature changes and sunlight. A body passing in front of thesensor willactivatefirstoneand then the otherelement whereas othersourceswillaffect both elementssimultaneously and be cancelled. The radiation sourceWORD格式 - 可编辑must pass across the sensor in a horizontal direction when sen

16、sor pins 1 and 2 are on a horizontal plane so that the elements are sequentially exposed to the IR source. A focusing device is usually used in front of the sensorThe figure below shows the PIR325 electrical specifications and layout in its TO5 package. Note the wide viewing angle without an externa

17、l lens.WORD格式 - 可编辑This is a typical application circuit that drives a relay. R10 and C6 adjust the amount of time that RY1 remains energized after motion is detected. Download PDF drawing.WORD格式 - 可编辑Fresnel LensA Fresnel lens (pronounced Frennel) is a Plano Convex lens that has been collapsed on i

18、tself to form a flat lens that retains its optical characteristics but is much smaller in thickness and therefore has less absorption losses.Our FL65 Fresnel lens is made of an infrared transmitting material that has an IR transmission range of 8 to 14um which is most sensitive to human body radiati

19、on. It is designed to have its grooves facingWORD格式 - 可编辑the IR sensing element so that a smooth surface is presented to the subject side of the lens which is usually the outside of an enclosure that houses the sensor.The lens element is round with a diameter of 1 inch and has a flange that is 1.5 i

20、nches square. This flange is used for mounting the lens in a suitable frame or enclosure. 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 length of 0.65 inches from the lens t

21、o the sensing element. It has been determined by experiment to have a field of view of approximately 10 degrees when used with a PIR325 Pyroelectric sensor.WORD格式 - 可编辑This relatively inexpensive and easy to use Pyroelectric Sensor and Fresnel Lens can be used in a variety of science projects, robot

22、s and other useful devices.3.1 Focusing devices for pyroelectric infrared sensorsA.1 Pyroelectric infrared sensorsA.2 First we will look at a pyroelectric infraredWORD格式 - 可编辑sensor and see how it is made and why a focusing device is necessary. A commonly used pyroelectric infrared sensor has two se

23、nsing elements internally connected in a voltage bucking configuration.A pyroelectric sensor has an infrared filter window that admits IR within the 5 to 15 micrometer wavelength range. One end of the two series-connected elements in an analog sensor is connected to pin 3 that is normally grounded.

24、The other end connects internally to the gate of a Field Effect Transistor and to a very high value pulldown resistor. Power is applied to FETWORD格式 - 可编辑drain pin 1 and the output signal comes from FET source pin 2 which usually connects through an external pulldown resistor to ground and to an amp

25、lifier. A digital sensor not shown here, includes internal processing circuits and outputs digital pulses.A.3 The sensor is housed in a TO5 type package. Sensing elements are each 0.039 inch (1mm) wide and are spaced 0.039 inch (1mm) apart.WORD格式 - 可编辑A.4 Environmental conditions such as temperature

26、 changes and sunlight will affect both elementssimultaneously and will produce thesame amount of output from each element but of opposing polarity and will therefore be cancelled. The sensor will only produce a change in its output voltage when one of its elements is exposed to achange in radiation

27、and the other is not exposed.An IR emitting body moving across the front of a sensor will expose first one, then both and then the other sensorWORD格式 - 可编辑element.The output signal waveform from an analog sensor shows that for motion in one direction, first a positive, then zero and then a negative

28、transition results. Motion in the other direction will produce first a negative, then zero and then a positive transition.A.5 When a lens is not used in front of a sensor andan IR emitting body is close to the sensor, aboutWORD格式 - 可编辑3 or 4 feet and it moves across the front of the sensor, the radi

29、ated IR will expose one element more than the other and a voltage output will result. However, when the IR emitting body is further away from the sensor its radiation pattern becomes blurred and both elements are exposed more equally, resulting in no voltage output. The limited detection range is du

30、e to a lack of unequal exposure. Placing a lens in front of the sensor extends its detection range.A.6 The Fresnel lensthatA.7 A Fresnel lens is a Plano Convex lens that has beencollapsed on itself to form a flat lens retains its optical characteristics but is much thinner and therefore has less abs

31、orption loss.A Fresnel lens is usually thin and flexible and is about 0.015 inch (0.38mm) thick with grooves molded into one surface.WORD格式 - 可编辑The groove side of the lens usually faces the PIR sensor.A Fresnel lens both captures more IR radiation and focuses it to a small point. This focal point m

32、oves across the sensor as the IR source moves and exposes one elementWORD格式 - 可编辑at a time. A Fresnel lens can extend detection range to about 100 feet.A Fresnel lens will give the best possible performance, however other devices can be used to extend range.Although the following devices may not fit

33、 the description of a lens, we will call them lenses anyway.This diagram shows IR exposing both elements equally when no lens is used.Shadow lensSince simultaneous exposure of both elements is the cause of limited detection range, all we need is some method of preventing the IR from exposing both el

34、ements simultaneously as the IR emitting body moves across the front of the sensor, even at greater distances from theWORD格式 - 可编辑sensor. The sensor elements are 0.039 inch (1mm) wide and are spaced 0.039 inch (1mm) apart. If we place a thin vertical strip of IR opaque material about 0.060 inch (1.5

35、mm) wide centered in front of the sensor we can prevent some of the IR from striking the surface of the sensor 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 example the IR still exposes both elements

36、 equally.By placing a baffle or mask in front of the sensor, we can block some of the IR and produce a shadow on the sensorThis next figure shows what happens when the IR emitting body moves across the front of the sensor even at greater distances. The baffle allows full exposure ofWORD格式 - 可编辑eleme

37、nt 1 while blocking the IR so it produces a shadow over element 2 and does not expose it. This simple lens extends detection 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 (25mm) in front of the sensor. The greater s

38、pacing gives a narrower detection angle.This same idea can be expanded to produce a wide angle lens. Multiple baffle strips can be placed in front of the sensor to alternately block IR from one sensor element at a time even when the IR emitting body is at greater angles to the front of the sensor.WO

39、RD格式 - 可编辑This multiple baffle shadow lens provides a wide detection angle. The lens should be curved so all baffles are the same distance from the front of the sensor.Pinhole lensAnother simple focusing device that will expose one PIR sensor element at a time can be made using a thin piece of IR op

40、aque material with a hole in it that will function as a pinhole lens similar to the lens of a pinhole camera. The function of a pinhole camera lens is described in .The lens hole in a camera is usually small but canbe much larger in a sensor application where imageWORD格式 - 可编辑detail is not necessary

41、 and only the IR radiation from the animal must be focused onto one sensing element at a time. IR in the 5 15 micrometer wavelength range 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 spacing is not c

42、ritical but it should be about inch (12mm) to 1 inch (25mm) from the front of the sensor. A detection range of up to 20 feet can be obtained 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 obtained by placing several holes in the lens material and curving the lens in front of the sensor so all holes are an equal distance from the front of the sensor. Another type of lens can be made by placing a tube about 3/8 inch (10mm) diameter and 2 inch (50mm