INTELLIGENT GAS-SENSING USING AN INTEGRATED SENSOR PAIR

The performance of conductometric gas sensors (e.g. semiconducting oxide) is often reduced by the poisoning of the active film or by poor long-term stability of the output signal. In this paper we propose the use of an integrated pair of sensing elements, one with a narrow electrode gap and the other with a wide electrode gap compared with the film thickness, to recognise or overcome these disadvantages. Equations are 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 type 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 to improve sensor stability by eliminating undesirable common-mode signals. The basic principles apply to several classes of materials including both organic semiconductors (usually type I) and inorganic semiconductors (usually type II).