CO gas detecting device and circuit for driving the same

A CO gas detecting device comprising:

• a CO gas sensor provided with a gas sensitive member comprising an oxide semiconductor whose resistance value is changed when contacted with a reducing gas, a pair of electrodes provided on said gas sensitive member, and a catalyst layer comprising one or more catalyst metals selected from the group consisting of Pt, Pd and Rh and at least one carrier selected from the group consisting of Al.sub.2 O.sub.3, ZrO.sub.2 and SiO.sub.2, provided on said gas sensitive member;
• and
• a reference sensor substantially without sensitivity to CO gas provided with a gas sensitive member comprising an oxide semiconductor whose resistance value is changed when contacted with a reducing gas, a pair of electrodes provided on said gas sensitive member, and an insulative catalyst layer comprising Ag and at least one carrier selected from the group consisting of Al.sub.2 O.sub.3, ZrO.sub.2 and SiO.sub.2, provided on said gas sensitive member
• wherein said catalyst layers of each of said sensors comprise said catalyst metals in an amount of from about 0.05 to 20 wt. % based on the catalyst carrier in a thick film of from 10 to 50 .mu.m and from about 1 to 90 wt. % based on the catalyst carrier in a thin film of from about 5 to 1000 nm, such that the amounts of said catalyst metals are below levels at which the electroconductivity of said layers hampers measurement of said resistance value.