Gas detection with infrared absortion

Many substances are absorbing infrared light. They take energy out of infrared light in order to trigger an atomic oscillation. A typical example is the C – H bond in hydrocarbons. To trigger the oscillation, a well – defined frequency of the light is required. Infrared gas detectors use this effect for gas detection. The absorption wavelength of different substances is very specific, just like a fingerprint, but the absorption at 3.4 mm is common for all hydrocarbons.


An infrared gas detector consists of a light source and two light detectors. The light is divided into two beams, one with 3.4 mm wavelength and a reference beam with a different wavelength, at which the gas not absorb light. If hydrocarbon gas enters the cuvette, it consumes energy out of the 3.4 mm beam, while the reference beam is not affected. The bigger difference between the two detector signals, the more gas is present.

Gas detection with infrared absorption is very useful to detect gases which are not very reactive, and gas mixtures without oxygen. Another big advantage is, that this method is resistant against corrosive gases or catalyst poison.  It is not suitable to detect gases which are not hydrocarbons such as ammonia or carbon monoxide.

The expected lifetime of infrared gas detectors is several years. Even if an infrared gas detector fails, the failure can never go unnoticed: As well a light source damage as a failure of a light detector will be detected as full – scale gas detection.

Compur Monitors safe and reliable infrared gas detection

The infrared gas detector family from Compur Monitors is mainly used in the chemical and petrochemical industry. Statox 501, Statox MC IR, Statox LC IR and Infratox offer utmost plant safety and industrial hygiene.