Evaluation of commercial metal-oxide based NO2 sensors

Purpose - Selection of a gas sensor requires consideration of environmental effects that can significantly affect performance and cause false alarms. Metal-oxide sensors have high sensitivity due to the specific interactions of gas molecules with thin metal-oxide films, however, the films can also be sensitive to variations in temperature and humidity and some oxidizing and deoxidizing gases. The purpose of this paper is to evaluate the environmental effect on metal-oxide nitrogen dioxide (NO2) sensors quantitatively. Design/methodology/approach - Three commercial metal-oxide NO2 sensors and one electrochemical sensor were tested simultaneously under controlled gas concentrations and various environmental conditions. For this test, a customized sensor testing setup was prepared including a gas mixer, heating module, gas chamber, electronics, and data acquisition units. Findings - Based on the test results for NO2 gas concentrations ranging from 0 to 10 ppm, the metal-oxide sensors showed significant signal variations at elevated temperatures and humidity. The results provide overall sensor performance. Linearity, repeatability, selectivity and sensitivity of the metal-oxide sensors were measured and compared to an electrochemical sensor. Originality/value - A systematic evaluation to characterize metal-oxide NO2 sensors is presented, and their comparison regarding sensitivity, selectivity linearity; and dependence on humidity and temperature is reported. The result provides sensor performance data and guideline for sensor evaluation.