HIGH-TEMPERATURE HUMIDITY SENSOR USING A LIMITING-CURRENT-TYPE PLANE MULTI-OXYGEN SENSOR FOR DIRECT FIRING SYSTEM

A high-temperature humidity sensor for use in ambient atmospheres has been developed, the first in industry, using a limiting-current zirconia solid-electrolyte planar oxygen sensor. We have now developed a multisensor capable of measuring both the humidity and oxygen content simultaneously by further improving the features of the planar electrode configuration of this high-temperature humidity sensor. In considering the application of this sensor to direct firing or combustion systems, we have investigated the individual effects of concentrations of O-2, CO2, CO, and NOx upon the water vapor pressure measurements. As a result, we find that the oxygen concentration has the most effect, and also that, in parallel with theoretical studies, approximately correct water vapor pressure measurements can be obtained when the data are compensated with respect to the oxygen concentration. We shall also report the effects of CO2, CO, and NOx. We verify that practical high-temperature humidity sensors can be realized for use in direct firing systems by using this multisensor.