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Photoelectric Smoke Detector

Photoelectric And Ionization Smoke Detectors

By Tricia Jones on September 20, 2010

There are different types of smoke detectors that have been developed for various purposes. The importance of detectors is being realized through the level of safety they provide to industries and also in residences. The types of smoke detectors that are widely used are ionization detectors and photoelectric detectors. Ionization detectors use a detection chamber and ionization radiation as its source. The source of ionization radiation contains at least 1/5000th of americium-241 which produces alpha particles from nuclei of helium elements. The ionization chamber is composed of two plates having a centimeter distance between them. A battery is used to apply voltage to charge one plate positive and the other negative. The americium-241 releases alpha particles to knock off electrons of the atoms in the chamber causing the positively charged oxygen and nitrogen atoms to bond with the surface particles of negative plate and electrons are attracted to the positive plate, producing a minute and continuous electric current.

The drop in current between parallel plates causes the alarm to set off. This happens when the ionization chamber senses smoke whose particles automatically attach to the ions to neutralize and prevent them to reach the plate. Another type of smoke detector is the photoelectric detector. The photoelectric device allows the smoke to block a light beam. This means a reduction in light going to a photocell. When this happens, alarm sets off. In the photoelectric unit there is a T-shaped chamber containing a light emitting diode (LED) that focuses the beam of light across the horizontal bar of the T. At the bottom of the vertical base of the T, a photocell is placed to produce a current upon exposure to the light. If there is no smoke, the light beam crosses the top of the T in straight line. When smoke enters the T-chamber, its particles cause the light to bend towards the photocell. When the photocell is hit by sufficient light, the current sets off the alarm.

Photoelectric detectors are as effective as ionization detectors in sensing smoke. Ionization unit responds to flaming fires with smaller particles; photoelectric detectors respond more quickly to all fires. Photoelectric detectors are more expensive than ionization units but the latter provides a level of built-in security not found in photoelectric detectors. The difference between these detectors is also apparent during the change of batteries. The alarm of ionization detectors sound to hint that the battery should be changed. The sound is caused by the drop in the ion current. In contrast, photoelectric detectors can be provided with back-up batteries, but don't provide this added benefit

Original article published on SooperArticles.com

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