Testing the reliability of humidity sensors through prolonged measurements traceable to calibration standards

This study looked at the accuracy of relative humidity sensors over a seven-month period at five locations. They were subjected to monthly traceable calibration in a climate-controlled chamber. We found the calibration output variance within sensors was smaller (0.4 ± 0.2 %RH: n= 5 sensors, each of which was exposed to nine humidity levels in the climatic chamber) than the manufacturers specifications (± 3.5 %RH). The study found differences in sensor output variance, which might be related to their working environment. Powered sensors in low ambient RH environments showed minimal differences over time (p > 0.05) when compared to powered sensors exposed to higher humidity environments (p < 0.05). To the author's knowledge, there have been no previous reports on stability of calibration of humidity sensors over prolonged periods (seven months). This work gives the first indication of stability in relation to environmental conditions of use. It can be concluded that sensors should obtain regular recalibration if used continually (suggested every 6 months), however those in higher humidity environments appear to require more frequent re-calibration (approximately every 3 months).