Heater power supply fluctuations in metal oxide gas sensors: impact on gas sensing performance

Abstract

This work reports the impact of deviations in heater current caused by an imprecise 5V power source on the parameters utilized in gas sensing modules in MQ series towards 62 ppm of Ethanol vapor. The gas sensing experiments involved three MQ series gas sensors under lab-made chamber for continuous Ethanol vapor measurement. To investigate how heaters’ current irregularities, affect the gas sensing performance parameters, the sensor’s response/recovery time, pattern recognition techniques of principal component analysis (PCA) and hierarchical cluster analysis (HCA) were employed. While minor voltage drops (±100 mV) may not significantly affect sensing resistance (R_S) due to real-time input voltage (Vin) adjustment, a constant current source is essential for heating resistance (R_H). The study revealed that a slight increase (±3 mA) in heater supply, particularly from 154 mA (94 °C) to 157 mA (96 °C), can significantly accelerate the recovery time (Trec) of the MQ-7 sensor from 484 s to 316 s, resulting in a difference of over 150 s. This improvement can be attributed to the desorption of gas molecules at higher temperatures, aiding in sensor cleaning. However, this small change does not significantly affect the response time (Tres), which remains between 245 and 295 s at worst. Our gas sensor exhibits enhanced sensitivity and operational stability thanks to a calibrated circuit and stable 5V power supply. Strong correlations between normalized response and sensing films’ temperatures, with a correlation coefficient of 0.985, provide insights into the relationship between heater currents, temperature effects, and gas sensitivity. These findings offer insights for optimizing sensing performance under gas exposure conditions.