Dewpoint Measurement in gases - Transmitters and Analyzers
Optimal dew point measurement with DKS
Al2O3 (aluminum oxide) is most frequently used here. Due to its interactions with water, the oxide is considered a sensitive layer and is used for moisture sensors. The water accumulates on the surface of the metal oxide. The sensor is built up in two layers. The base electrode is made of aluminum on which the porous oxide layer is applied. The best way to compare the sensor is to due that with a capacitor. A water-vapor-permeable thin layer of gold is applied to the counter electrode. The sensitive layer must be as large as possible in order to be highly sensitive. The water vapor passes through the gold layer into the pores of the sensitive layer and accumulates. Chemical sorption separates the water molecules on the surface into a hydroxyl group. Additional water molecules can now be bound to the hydroxyl groups by "Van der Waals" forces. The bound water molecules are now in equilibrium with the surrounding air humidity and influence the capacity and thus the conductivity of the "condenser". A measured value is then obtained by a comparatively simple impedance measurement. There is a good correlation to absolute humidity. The aging effects of the sensitive layer require regular calibration, which cannot be carried out by the end customer. The process is also not suitable for aggressive gases.