Investigations on Capacitive-based Relative Humidity Sensors and Their Stability at High Temperature

The performance of high-temperature, polymer-based RH sensors was investigated in order to evaluate their long-term stability. The work is aimed at understanding howsevere temperature cycles may alter the characteristics of relative humidity (RH) sensors, how they impact the measurements, and how they contribute to the measurement uncertainty. The tests involved 10 high-temperature RH sensor probes available from five European manufacturers. They were initially calibrated against suitable humidity standards in the range from 10%rh to 85%rh with air temperatures from 20 ◦C to 80◦C, and subsequently, they were exposed to air temperature at about 145 ◦C for several cycles, each cycle lasting (50–100) h. After each high-temperature exposure, a calibration check at 80 ◦C was carried out. The test lasted until the sensor exposure time exceeded 300 h. The paper presents the characteristics of such probes, the investigation results, and the comparison of the specified versus the experimental performances.