Abstract: A gas sensing thick film is positioned on an insulating substrate in contact with a pair of electrodes. A non-porous glass layer surrounds the film to stabilize it on the substrate. A heating element maintains the film at a preselected elevated temperature. The gas sensing thick film has a response characteristic for a preselected target gas to be detected which is enhanced by impregnating the film with platinum or palladium chlorine free compounds. The response characteristic of the gas sensing film is further increased by promoting combustion of interference gases on an outer filter layer fabricated of either conductive or nonconductive material. The incorporation of an insulating material between the gas sensing film and the outer filter layer also serves to increase the relative response of the gas sensing film to a preselected target gas.

Abstract: A gas sensing instrument provides programmable control of the operating temperatures of an array of gas sensors for the detection of target gases in air. The control facilitates precise temperature setpoint resolution. The gas sensors in the array have an improved construction density with reduction in size and an extended operating life provided by reduced power consumption. A programmable circuit functions as a programmable-resistor temperature controller in a Wheatstone bridge configuration. A multiplying digital to analog converter circuit controls the ratio of voltage to current that functions as a resistance equivalent. The programmable circuit is interfaced with a computer to provide selectable temperature control for at least 256 setpoints.