The influence of relative humidity on the response of tin oxide gas sensors to carbon monoxide

Abstract It is well known that the selectivity of tin oxide gas sensors is not very good. In particular, if the sensors are submitted to real life conditions, their response becomes ambiguous because of ambient water vapour. There are several techniques to cope with this problem. A first method to decrease the influence of the relative humidity is to incorporate additives into the tin oxide. However, with this method it is impossible to eliminate the influence of water to an acceptable level. Another method is to use an array of sensors and to convert the response of this array by means of mathematical algorithms, in order to obtain a response that is insensitive to water vapour. The method presented in this paper consists of switching a single tin oxide gas sensor between two well-defined temperatures. With this method, it is possible to decrease the sensitivity to water vapour to an acceptable level, while the high sensitivity to CO is unaffected.