Resistive humidity sensors

These sensors consist of a polymer film or polymer treated substrate which separates two electrodes in a porous probe. The probe is brought into equilibrium with a gas. The substrate either adsorbs or desorbs moisture depending on the changes in RH value. Changes in the electrical impedance of the hygroscopic substrate medium are then measured by the resistive humidity sensors. A well-defined relationship exists between RH with the sensor capacitance and the sensor resistance for a known polymer sensors. The laboratory measurements of either sensor capacitance or resistance could be used to back analyze the RH value using the well established calibration curves. The calibration curves for these sensors as reported by Lu and Likos (2004) are shown in Fig. 4.19.

The advantage of these sensors is that they are applicable for wide range of RH variations and exhibit low hysteresis, albeit inexpensive to use. Further, these sensors are known for quick measurements as the response time is typically less than 30 seconds. It was reported by Lu and Likos (2004) through few research citations that these sensors exhibited good measurement precision and have excellent practical applications in the bench scale study of alternative earthen fill cover.