Characterizing the Effect of Simultaneous Enhancements of Reducing Gas Species on Figaro Taguchi Gas Sensor Resistance Response

The resistance of the Figaro Taguchi Gas Sensor (TGS) decreases when exposed to reducing gas enhancements. TGS gas response can be characterized by comparing measured resistance to a reference resistance, representative of sampling in identical environmental conditions but with no reducing gas enhancement. Thus, this resistance ratio (RR) allows for characterization of reducing gas response, independent of other environmental effects. This work presents controlled laboratory experiments, measurements, and modeling for an analysis on the effect of reducing gas cross-sensitivities on RR. The methane mole fraction ([CH₄]) was raised to approximately 9 ppm from a 0.492 ppm reference level, and carbon monoxide mole fraction ([CO]) was raised to approximately 4 ppm from a 0 ppm reference level, through multiple simultaneous steps. The independent effect of each gas on RR was directly multiplied, resulting in an inferior RR compared with measurements, implying an interdependence effect. For example, for one TGS unit, when deriving [CH₄] from RR, a 6 ppm [CH₄] measurement would be underestimated by 6% at 1 ppm [CO], but only by 1.6% at 0.1 ppm [CO]. A key implication of residual interdependence effects is that any gas characterization must be conducted with the same reference levels of each other reducing gas expected during field deployment, even if measuring a single gas. A first-order interdependence correction is proposed to account for such interdependence effects. Yet, each TGS behaves differently, and interdependence testing takes time. Therefore, the TGS best serves to detect single reducing gases, assuming all other reducing gases to remain constant at their reference levels.