Fire Detector

Fortunately elaborate fire detector systems such as those used in large buildings are not necessary for a private home. While it is wise to take precautions to prevent fires from starting, it is also wise to install a fire detector in your home just in case you do need a warning in case some accident does happen. With fires, time is all important and can mean the difference between life or death so the earlier the fire detector sounds the alarm, the better.

Although one type of fire detector is most usual in domestic alarms, we will take a look at the others so as to appreciate why they are used and where, and the reasons one type of fire detector is more suitable for domestic applications.

The optical smoke detector is a fire detector that uses the Tyndall effect, whereby light is scattered by particles of smoke. A small radiator directs a pulsed beam of infrared light at an angle into a detection chamber, while an infrared detector 'looks' into the chamber. As the chamber is matt black inside, no infra-red is reflected and the fire detector sees nothing.

If smoke enters the chamber, the infrared is scattered in all directions by the smoke particles and some is seen by the detector. The first few pulses are ignored to prevent false alarms from random dust particles, but any after that trigger the alarm circuit of the fire detector.

The ionization smoke detector is another type of fire detector. This fire detector has a small low-level radioactive radiation source such as americium 241 which maintains a flow of ions through the air in the detection chamber of the fire detector to a pick-up electrode. Smoke particles entering the chamber pass between the source and the electrode and reduce the flow. The drop in electrode current is sensed by a comparator circuit which triggers the fire detector alarm.

Infrared beam detection is another type of fire detector. The lamp and the fire detector face each other a high level where the beam will not be interrupted by any object or person. Smoke reduces the amount of infrared reaching the fire detector and an alarm is sounded when the circuits sense a drop. A delay in the response is usually incorporated to ignore momentary interruptions that could give a false alarm.

Another type of fire detector is the flame detector. This fire detector responds to infrared or ultraviolet radiation given off by the flames. The infrared type distinguished between flames and other sources of infrared such as heaters or persons by sensing flame flicker. Steady sources are thus ignored by the fire detector.