Sensing different mixtures of H2, CH4 and CO through an array of chemiresistors

This work proposes a set up for sensing H₂, CH₄ and CO generated from biomass. The sensing is performed by commercially avaliable SnO₂ chemiresistors [6], one for each gas. The proposed set up has a gas dilution stage before the sensing step. One hundred and twenty five different gas mixtures were prepared from the combination of H₂, CH₄ and CO using nitrogen as carrier gas. The samples were evaluated under two different methods for sensor recovery: forced and natural. Based on the results, it was established that the cross sensitivities of the CO and CH₄ sensors are too high while the H₂ sensor presents selectivity of almost 100%. Also, the natural recovery method showed improved results because of the better thermal stability of the system. An artificial neural network was developed with the purpose of overcoming the problem of cross-sensitivities and indicated a minimum squared error energy (SSE) of 8.5×10^-8 for H₂, 2.0×10^-3 for CH₄ and 5.1×10^-3 for CO.