Author: Hans-Jürgen Schwarz
back to Air Humidity Measurement
The resistive sensors take advantage of the effect, that a material, which has been coated with a hygroscopic and ionically structured substance (e.g. LiCl) changes its conductivity with increasing moisture content. Because this moisture content is in equilibrium with the humidity in the ambient air, the relative humidity (RH) can be detected. The relationship between RH and conductivity is exponential. There is also an interdependence with temperature. The sensors are susceptible to chemical influences and freezing, but show a low tendency for drift and nearly no hysteresis. They are therefore particularly useful for the recording sorption isotherms. These sensors are less suitable for detecting low humidity levels, since the resistance increases with exponentially decreasing humidity. The measuring effect is relatively large, resulting in small demands on the subsequent electronics. It is therefore possible to produce relatively low-price measuring units. However, the sensors need to be calibrated separately.