Recognition of Indoor environmental gases using two sensing films on a substrate

Indoor environmental toxic gases by using a temperature modulation method with a tin oxide gas sensor were monitored. The sensor Was consisted of a Pt temperature sensor, a Pt heater, and SnO₂ and SnO₂/Pt sensing layers on an alumina substrate. Species and concentrations of used indoor environmental gases for the SnO₂ and SnO₂/Pt sensing layers were air, carbon dioxide (2500 and 5000 ppm), methane (5000 and 10000 ppm), propane (2000 and 4000 ppm), and butane (1800 and 3600 ppm), respectively. A gas concentration corresponding to the threshold limit values or the lower explosive levels of test gases was selected. Using a temperature modulation with a trapezoid shape, we got response curves from both SnO₂ film and SnO₂/Pt film. Various parameters from the response curves of the two sensing materials were extracted and a principal component analysis was adapted in these parameters. Combining a simple design device with two sensing films, the proposed temperature modulation, and a statistical method, we confirmed that the present method was very effective in monitoring of indoor environmental gases. Therefore, a real alert system can be implemented in a indoor environment.