SELECTIVE THERMALLY CYCLED GAS SENSING USING FAST FOURIER-TRANSFORM TECHNIQUES

The conductance versus time signatures of three types of thermally cycled gas sensors have been measured for a number of different reducing gases over a wide range of concentrations. A fast Fourier-transform data analysis technique is used to produce first-harmonic polar plots of phase angle versus magnitude of both single gases and mixtures as a function of concentration. It is found that this produces a good separation among many of the gases tested and leads to a clear selective criterion for the detection of single unknown gases. Gas mixtures can sometimes be distinguished as well, but with less reliability.