Dynamic model to estimate the dependence of gas sensor characteristics on temperature and humidity in environment

A gas sensor using tin oxide changes its electrical resistance (R_s) with a change in the concentration of a reducing gas (C). However, the R_s vs. C correlation is affected significantly by the temperature (t) and relative humidity (h) of the surrounding atmosphere. We propose a dynamic model to describe the influences of t and h. As is well-known, the R_s vs. C correlation was expressed satisfactorily by an equation, log₁₀ R_s = α log₁₀ C+β (α and β constant), under fixed conditions of t and h. Analysis of the observed data indicated that the values of α and β under various environmental conditions were distributed along a plane when plotted three-dimensionally against t and h. This fact allows to propose a simple model in which both α and β are linear functions of t and h, respectively. The three constants included in each function were determined experimentally. The resulting equation of α and β were found to describe the R_s vs. C correlation well under various conditions of t and h.