Humidity measurement with capacitive humidity sensors between −70°C and 25°C in low vacuum

Abstract. At the German Aerospace Center (DLR), capacitive humidity sensors are used to measure relative humidity in experiments under extreme atmospheric conditions such as on Mars or in the coldest regions on Earth. This raises the question whether such experiments can be performed using low-cost humidity sensors with a tolerable measurement uncertainty. As part of the standardizing project SMADLUSEA (project no. SF11021A), nine capacitive humidity sensors (Sensirion SHT75) were investigated for pressure ranging from 10 to 1000 hPa (low vacuum) and temperatures from −70 to 25 °C. It has been shown that these sensors worked reliably and with reproducibly measured values over the entire investigated pressure and temperature range. There was no aging of the sensors observable. In addition to the known strong temperature dependency, the SHT75 also shows a pressure dependency below −10 °C. A characteristic curve for the SHT75 was calculated with an expanded uncertainty of 7% of the measured values.

In conclusion, low-cost capacitive humidity sensors offer the option to obtain reliably measured values even under extreme conditions with comparatively little effort.