INTELLIGENT GAS-SENSING USING AN INTEGRATED SENSOR PAIR

The performance of conductometric gas sensors (e.g. semiconducting oxi de) is often reduced by the poisoning of the active film or by poor lo ng-term stability of the output signal. In this paper we propose the u se of an integrated pair of sensing elements, one with a narrow electr ode gap and the other with a wide electrode gap compared with the film thickness, to recognise or overcome these disadvantages. Equations ar e derived that describe the steady-state response of such a device for the two limiting cases of a uniform gas concentration within the film (type I) and a distance-dependent one with a boundary (type II). The characteristic response, or operating curve, of a sensor pair for a ty pe I material can then be used as a realtime diagnostic for poisoning of the film, whereas the response for a type II material can be used t o improve sensor stability by eliminating undesirable common-mode sign als. The basic principles apply to several classes of materials includ ing both organic semiconductors (usually type I) and inorganic semicon ductors (usually type II).