Infrared Gas Detectors make use of the property of Hydrocarbons and other gases to absorb infra-red energy at certain wavelengths but not others. For HCs the absorption peak occurs around 3.4 µm.
A reference measurement is normally made close to the measurement wavelength that is not absorbed by expected gases.
The ratio from the two measurements gives the gas concentration free from variations in signal intensity and detection sensitivity.
Set Point: Infra-red detectors have a typical recommended minimum alarm setting of 20 % LFL and 60 % LFL to indicate low and high level of gas