Discrimination of a refrigerant gas in a humidity controlled atmosphere by using modelling parameters

For real life conditions of use, the application based on tin oxide gas sensors must be humidity controlled, because humidity is a very influent parameter which may cause false gas detection. In our application, we want to distinguish a refrigerant gas (Forane R134a) in an air conditioned atmosphere using a TGS gas sensor array. At first, this paper presents a summary of the sensor array time-dependent response in a Forane R134a gas concentration (0-1000 ppm) for a humid air atmosphere (0-85%). We show that these responses can be well fitted by a double exponential model for which we extract five modelling parameters. These variables are coupled or not with two experimental parameters, the steady-state conductance and the conductance dynamic slope, and then arranged in data bases. Afterwards, these data bases are treated by using two complementary pattern recognition methods: the principal component analysis (PCA) followed by the discriminant factorial analysis (DFA). We show the ability to discriminate the target gas, whatever the humidity rate, when the modelling parameters are coupled or not with the experimental parameters. Finally, the identification of unknown cases is described. (C) 2000 Elsevier Science S.A. All rights reserved.