FLAME DETECTOR (INFRA-RED TYPE)
In addition to light, fires generate infrared and ultraviolet radiations which are less affected by smoke than normal white light.
By employing a photoelectric cell with infrared filters or an ultraviolet sensor, the presence of flames can be detected in spite of the smoke generated.
The signal from the photoelectric cell with infrared filters or an ultraviolet sensor can be arranged to trigger the alarm.
These devices suffer from the disadvantage that they will react to infrared or ultraviolet radiations from other sources and hence are prone to spurious alarms.
This disadvantage is overcome in a combined smoke and heat detecting system in which a modulated infrared beam is transmitted across the area to be protected.
Smoke and heat haze interfere with the beam and this is detected in the receiving unit which initiates the alarm.