Patent ID: 7007542

Claim:
A method for determining poisoning of a gas sensing element comprising the steps of: a) forming an apparatus for detecting a combustible gas comprising: a gas sensing element including an electric heating element, a first layer coated on the electric heating element and comprising a precious metal catalyst supported on a porous oxide, the precious metal catalyst catalyzing combustion of a combustible gas to be detected by the sensing element, and a second layer overlaying the first layer, and comprising a catalytic compound capable of trapping gases which poison the precious metal catalyst, said catalytic compound being supported on a porous oxide; a compensating element comprising an electric heating element, said compensating element not including a catalyst capable of catalyzing combustion of a combustible gas to be detected by the sensing element; and an electrical circuit to which the sensing element and compensating element are connected, said electrical circuit being constructed and arranged to detect changes in resistance of the sensing element and compensating element, and to provide a reading of said changes; b) operating said apparatus in an atmosphere substantially without combustible gases to determine a baseline reading for said apparatus; and c) continuing to observe said baseline reading, with a drift of baseline indicating poisoning of said gas sensing element.