Sensitivity, response and recovery time of SnO2 based thick-film sensor array for H2, CO, CH4 and LPG

This paper deals with the studies carried out on sensitivity, response and recovery time of a sensor array comprising of undoped and doped (palladium, platinum and gold) thick-film SnO2 sensors. Initially, the sensitivity of all the sensors of the array has been studied for H-2, CO, CH4 and LPG followed by detailed analysis of transient response of Pd-doped sensors as it possesses better sensitivity for all the test gases. The response and recovery time of the Pd-doped sensor has been found to depend on type of gas and its concentration (upto 400 ppm). The response time is minimum for CO and maximum for H-2 while recovery time is maximum for LPG and approximately same for H-2 and CO. The observed results of response time have been explained on the basis of two-film theory, i.e. gas film-gas phase and solid-gas film interfaces. Further, the experimental result of the sensor array (sensitivity versus concentration and sensitivity versus response time) for all the test gases at an operating temperature of 350 degrees C have been validated with an analytical model and the observed results are found to be in good agreement to that predicted by the model. (C) 1998 Elsevier Science Ltd. All rights reserved.