Resolving combustible gas mixtures using gas sensitive resistors with arrays of electrodes

Gas sensitive resistors using semiconducting oxides operating at elevated temperatures and having an array of different electrode spacings on a single device are functionally equivalent to an array of different sensors with differing patterns of response to different gases. Here, a single device with two different electrode spacings is used successfully to distinguish between gases having different combustion rates, and to analyse binary mixtures of combustible gases at low concentrations in air. Furthermore it is shown that devices of this type provide considerable insight into the mechanisms of both the surface-catalysed combustion and the gas response. The kinetic law for the surface catalysed combustion of the target gas is derived by comparison with the results of numerical simulations using an iterative procedure based on the Newton-Raphson method. The accurate analysis of the gas mixtures forced a reformulation of the response model which, for a mixture of n gases is shown to be (R/R(0))(1/beta)-1=Sigma(j=1)(n) A(j)P(j) where R denotes the resistance (R(0) in air), A(j) the response coefficient and P-j the partial pressure of gas j. The response order, beta, is the same for all gases.