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

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 \((P_S) \) are functions of sensor circuit load resistance ( ). However, there is no well-established standard method for determining \(R_L\)  value that can simultaneously yield maximum sensor circuit sensitivity \((S_M) \) and acceptable  for a given value of gas concentration. To obtain optimum \(R_L, \) the dependence of \(S \)  and \(P_S \)on for a given gas concentration was thoroughly investigated. The model equations for determining \(S,P_S \) and \(R_L\)  at \(S_M \) \(R_(L,MAX)\) 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 \(P_S \)  with respect to \(R_L\) were investigated when each of the associated gases has concentration of 1000 ppm. The sensor circuit optimal  \(R_L \) must satisfy the dual conditions of (i) S= \(S_M \)  and (ii) \(P_S<set threshold.\)  Results obtained from the analysis revealed that the values of  \(R_(L,MAX) \) were 20, 24, 64, 120, and 152 \(kΩ \)  for liquefied petroleum gas (LPG), \(CH_4, \)\(H_2,\) alcohol and CO respectively, corresponding to sensor powers of 0.3125, 0.2589, 0.0977, 0.0521, and 0.0411 mW.