READIT-2007 - Indira Gandhi Centre for Atomic Research

sensing devices are named as sensors / detectors. The following are the various types
of Smoke sensors / detectors.
1. Ionization Smoke Detector
2. Photoelectric Smoke Detector
3. Optical Smoke Detectors. And
4. Beam Detector
Ionization Smoke Detectors:
Detectors sense the smoke arising out of
the bursting of fire is known as ionization
smoke detectors. In the event of fire, some
materials in Libraries and Archives may
generate or release a large amount of solid
particles, as constituent particles of
smoke, in the atmosphere. These types of
detectors are ideal for Libraries and
Archives.
Fig-3: Ionization Smoke Detectors
Heat Detectors: Heat Detector ideally suited to locations where high sensitivity is
required for change in heat and where smoke detectors are found unsuitable for
detection of fire. Generally, smoke detectors, do not work efficiently in the places
where material stores and produces little smoke in the initial stage of out breaking of
fire or where adverse environmental conditions are prevailing.
Optical Smoke Detectors:
An optical smoke detector
includes a light source
(infra-red LED) and a
photodiode or other
photoelectric sensor at
right-angles to the light
beam. In the absence of
smoke, the light passes in
front of the detector in a
straight line and light
sensor does not get any
light.
Fig-4: Optical Smoke Detectors
When the smoke enters into optical chamber, that is the path of the light beam, some
light is scattered by the smoke particles, and same is detected by the sensor. These
75