Infrared type flame detectors are normally used to protect large open areas where an immediate, flame-producing fire is expected such as in the protection of flammable liquid hazard.
Infrared type flame detectors
IR detectors are constructed essentially of a lens and filter system that screens out unwanted wavelengths and focuses the incoming energy on a photovoltaic or other type cell that is sensitive to infrared energy.
These types of detectors often also measure the infrared radiation emitted from a flame (spiking at the 4.3 micron peak radiation wavelength due to the presence of concentrated carbon dioxide within the flame) and characteristic flame flicker associated with the flaming mode of a fire that is in the 5 –30 Hz frequency range.
Infrared detectors can be subject to interference and false alarms from solar radiation if not properly applied. One method employed is to use multiple IR detectors to measure the amount of radiation in two or more wavelength bands to discriminate between a flame and other IR sources.