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 Ri.,wax were 20, 24, 64, 120, and 152 kH 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.