The partial water vapour pressure of compressed air changes in proportion to the absolute pressure of the gas being monitored. As each value of a particular water vapour partial pressure is associated with a specific dewpoint, the dewpoint also changes if the pressure changes. Measurement, however, is not pressure dependent and the dewpoint sensor always indicates the currently prevailing dewpoint at the measurement point, without a correction value being required. Adsorption and desorption effect, on the other hand, cause the more harmful distortions, the lower the dewpoint temperature. That is why one measures within the range at which the highest dewpoint is to be expected. With every pressure release of the measured air following the measurement chamber, heat is conducted from the surroundings, so that the release is accompanied by cooling. The lower temperature of the air being monitored resulting from this, leads to an increase in the adsorption inclination of the moisture in the air concerned. For this reason, the pressure release point in the piping should be followed by a calming stretch of about 2m length and of spiral shape.
