Advanced dew-point control system in two-pressure humidity generator to stabilize dew-point generation in low dew-point range

Abstract

We developed a novel dew-point control system [advanced dew-point control system (ADCS)] in a primary standard humidity generator based on the two-pressure technique. In the ADCS, the actual vapor–liquid equilibrium temperature of water was estimated for the dew-point control, and the pressure inside the main saturator was controlled by adjusting the variable opening of an expansion valve. Using the ADCS, the periodic variation (oscillation) in the dew point observed in the low dew-point range was greatly reduced. The stability of dew-point generation was improved by 23-fold.