Humidity measurements in carbon dioxide with Sensirion SHT85 humidity sensors under simulated Martian atmospheric conditions

Abstract

Humidity sensors that function under extreme conditions are needed in experimental chambers in which the atmospheric conditions near the surface of Mars are simulated, as well as for in situ measurements of humidity on the surface of Mars. Experimental setups with such sensors have already been constructed at the German Aerospace Center (DLR) and published. However, the SHT75 sensors from Sensirion used at that time are no longer in production and have been replaced by a new generation of sensors: SHT85. The SHT85 sensors are more precise than their predecessors, have a new sensor chip, and feature a PTFE membrane over the humidity-sensitive layer to protect the sensor from dust and liquids. The data interface to the I2C bus has also changed. Due to these significant changes, it was necessary to verify the sensor's capabilities under extreme conditions. For this purpose, the sensors were tested under the same conditions and in parallel to the calibration of the MEDA HS sensor from the Finnish Meteorological Institute (FMI), on board NASA's Mars 2020 rover. The results show that the SHT85 is, as its predecessor SHT75, suitable for measurements under Martian atmospheric conditions when the relative humidity is in the range higher 5 %.