Investigation of the humidity effects on SnO2-based sensors in CO detection

An algorithm for compensating H2O vapor pressure in CO detection is proposed here and tested on SnO2 thick-film gas sensors. For each sensor working at a fixed temp., the conductance, G, is fitted by an anal. surface, whose expression can be inverted to det. the CO concn. once the H2O partial pressure is measured. As soon as the rate of H2O-vapor pressure change is slower than .apprx.300 Pa/min, G is a function of the temp., H2O vapor and CO concn. If quicker H2O vapor variations occur instead, the sensing film undergoes a nonnegligible transitory phenomenon during which G assumes different values even at fixed H2O vapor pressure and temp. This phenomenon prevents the compensation from working properly. An explanation of the behavior is offered by the interpretation of kinetics equations at surface.