The infrared (IR) method of gas
detection relies on the IR absorption characteristics of gases to determine
their presence and concentration. IR gas detectors consist of an IR light
source (transmitter) and light detector (receiver) to measure the intensity
both at the absorption wavelength and a non-absorbed wavelength. If gas is
present in the optical path, it will affect the intensity of light transmitted
between the light source and the detector. This change in intensity provides
the data for determining that a specific gas or type of gas is present. This
method works only for gases that can absorb infrared radiation. Most
hydrocarbon based gases absorb IR radiation at around 3.4 micrometers, which is
transparent to both water and carbon dioxide vapors.Combustible IR gas detection can
take one of two forms: either the point detector or the open path detector. The
primary difference between point detectors and open path is the size of the IR
path and its relationship to the gas/vapor sample source. The self-contained
point detector has a smaller IR path than the open path detector, and is used
to monitor fixed areas of space. The open path detector usually consists of a
separate transmitter and receiver, which monitor much larger areas of space.
Consequently, in some instances a single open path detector serves the function
of multiple point detectors.
