两种烟雾传感器(原理及对比).doc

1、 There are two main types of smoke detectors: ionization detectors and photoelectric detectors. A smoke alarm uses one or both methods, sometimes plus a heat detector, to warn of a fire. The devices may be powered by a 9-volt battery, lithium battery, or 120-volt house wiring.Ionization DetectorsIon

2、ization detectors have an ionization chamber and a source of ionizing radiation. The source of ionizing radiation is a minute quantity of americium-241 (perhaps 1/5000th of a gram), which is a source of alpha particles (helium nuclei). The ionization chamber consists of two plates separated by about

3、 a centimeter. The battery applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the americium knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber. The positively-charged oxygen

4、 and nitrogen atoms are attracted to the negative plate and the electrons are attracted to the positive plate, generating a small, continuous electric current. When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they do not reach the plate. The dr

5、op in current between the plates triggers the alarm.Photoelectric DetectorsIn one type of photoelectric device, smoke can block a light beam. In this case, the reduction in light reaching a photocell sets off the alarm. In the most common type of photoelectric unit, however, light is scattered by sm

6、oke particles onto a photocell, initiating an alarm. In this type of detector there is a T-shaped chamber with a light-emitting diode (LED) that shoots a beam of light across the horizontal bar of the T. A photocell, positioned at the bottom of the vertical base of the T, generates a current when it

7、 is exposed to light. Under smoke-free conditions, the light beam crosses the top of the T in an uninterrupted straight line, not striking the photocell positioned at a right angle below the beam. When smoke is present, the light is scattered by smoke particles, and some of the light is directed dow

8、n the vertical part of the T to strike the photocell. When sufficient light hits the cell, the current triggers the alarm.Which Method is Better?Both ionization and photoelectric detectors are effective smoke sensors. Both types of smoke detectors must pass the same test to be certified as UL smoke

9、detectors. Ionization detectors respond more quickly to flaming fires with smaller combustion particles; photoelectric detectors respond more quickly to smoldering fires. In either type of detector, steam or high humidity can lead to condensation on the circuit board and sensor, causing the alarm to

10、 sound. Ionization detectors are less expensive than photoelectric detectors, but some users purposely disable them because they are more likely to sound an alarm from normal cooking due to their sensitivity to minute smoke particles. However, ionization detectors have a degree of built-in security

11、not inherent to photoelectric detectors. When the battery starts to fail in an ionization detector, the ion current falls and the alarm sounds, warning that it is time to change the battery before the detector becomes ineffective. Back-up batteries may be used for photoelectric detectors.主要有两种类型的感烟探

12、测器：电离检测器和光电探测器。烟雾报警器使用一种或两种方法，有时也加了热探测器，警告火灾。这些设备可以通过一个 9 伏电池，锂电池，或 120伏的室内布线供电。 离子化检测器 离子化检测器有一个电离室和电离辐射的来源。电离辐射的源是镅-241（一克的也许 1 /第5000） ，它是 粒子（氦核）的源极的微小量。该电离室包括由约一厘米分开的两个板组成。电池施加电压于板，充电一个板正面和另一板负。 粒子不断地释放由镅敲电子空气中的原子，离子化室中的氧和氮原子。带正电荷的氧和氮原子被吸引到阴极板和电子被吸引到正极板，产生一个小的，连续的电流。当烟雾进入电离室，该烟颗粒附着到离子和中和它们，所以它们不

13、到达板。板之间的电流的下降将触发报警。 光电探测器 在一种类型的光电器件，烟雾可以阻挡光束。在这种情况下，光的减少到达光电池设置关闭报警。在光电单元中最常见的类型，但是，光被散射的烟雾颗粒到一个光电池，启动警报。在这种类型的探测器有一个 T 形的腔室用的发光二极管（LED） ，该拍摄横跨 T 的水平杆光电管，定位在 T 的垂直底座的底部的光束，产生电流，当它暴露于光。下无烟条件，光束相交于一个不间断直线 T 的顶部，而不是撞击位于所述光束下面直角的光电管。当烟存在时，光被散射的烟雾颗粒，并且一些光被引导向下的 T 求取光电管的垂直部分。当有足够的光照射到电池，目前触发报警。 哪种方法更好？ 这两种电离和光电探测器是有效的烟雾传感器。这两种类型的感烟探测器必须通过相同的测试被认证为 UL 烟雾探测器。离子化检测器更快速地燃烧的大火与小颗粒的燃烧反应;光电探测器更迅速地对阴燃火灾作出回应。在任一种类型的检测器，蒸气或高湿度会导致凝结在电路板和传感器，从而使警报声。离子化检测器比光电检测器比较便宜，但有些用户故意禁止他们，因为他们更容易对声音从一般的烹调报警，由于其对微小的烟雾粒子的灵敏度。然而，离子化检测器具有一定程度的内置安全不是固有的光电探测器。当电池电量开始在离子化检测器失效时，离子电流下降，报警声音，警告，现在是时候更换电池前，探测器就失效了。后备电池可用于光电检测器。