SENSITIVITY AND SELECTIVITY OF DOPED SNO2 THICK-FILM SENSORS TO H2S IN THE CONSTANT-TEMPERATURE AND PULSED-TEMPERATURE MODES

The H2S response of some SnO2-based thick-film gas sensors containing Ag and Al2O3 has been studied in the concentration range 0 to 10 ppm. Several different operational parameters related to the response and recovery times, sensitivity and the interfering effects of NO, CO and H2O have been tested. The response measurements are carried out both in the constant-temperature and temperature-pulsed modes in order to find the advantages of each mode in relation to sensitivity, selectivity and response time. In the case of temperature pulsing, both the response and recovery times are very short compared to those in the constant-temperature mode. The constant-temperature mode, however, has to be used at concentrations below 0.5 ppm, which is about the observation limit in the case of temperature pulsing. The interfering effects of both CO and NO are small in the case of the constant-temperature mode, but very pronounced in the case of temperature pulsing. Some experiments concerning monitoring of H2S as a pollutant in city air have also been conducted with the present sensors.