In order to compensate for environmental influences like temperature, humidity, wind etc. a second coil without catalytic coating is used as an inactive compensation element. Both elements are electrically connected in a Wheatstone bridge.
If a combustible gas diffuses to the detector element, it is oxydized by the catalytic material. Since oxygen is required for the combustion, the sensor can only be used in ambient air.
The heat of the combustion produces an increase in temperature which results in a change of the internal resistance of the detector element. This change is proportional to the concentration of combustible gas and produces a misalignment of the Wheatstone bridge which after amplification is shown on a LCD display in % LEL.
