Determination of optimum load resistances of MQ-series gas sensor circuit for specific gas concentrations

Abstract

MQ-series gas sensors are frequently used in gas concentration sensing owing to their high sensitivity and relatively cheap cost. Reportedly, both the sensor’s circuit sensitivity (𝑆) and power dissipation (𝑃𝑆 ) are functions of sensor circuit load resistance (𝑅𝐿 ). However, there is no well-established standard method for determining 𝑅𝐿 value that can simultaneously yield maximum sensor circuit sensitivity (𝑆𝑀) and acceptable 𝑃𝑆 for a given value of gas concentration. To obtain optimum 𝑅𝐿 , the dependence of 𝑆 and 𝑃𝑆 on 𝑅𝐿 for a given gas concentration was thoroughly investigated. The model equations for determining 𝑆, 𝑃𝑆 and 𝑅𝐿 at 𝑆𝑀 (𝑅𝐿,𝑀𝐴𝑋) were derived and MQ-6 gas sensor’s response to its associated gases was used for demonstrating the proposed method. Variations of both 𝑆 and 𝑃𝑆 with respect to 𝑅𝐿 were investigated when each of the associated gases has concentration of 1000 ppm. The sensor circuit optimal 𝑅𝐿 must satisfy the dual conditions of (i) S=𝑆𝑀 and (ii) 𝑃𝑆 < set threshold. Results obtained from the analysis revealed that the values of 𝑅𝐿,𝑀𝐴𝑋 were 20, 24, 64, 120, and 152 kΩ for liquefied petroleum gas (LPG), CH4, H2, alcohol and CO respectively, corresponding to sensor powers of 0.3125, 0.2589, 0.0977, 0.0521, and 0.0411 mW.