Accurate and precise dew-point control system based on active pressure control in two-pressure humidity generator.

We developed an accurate and precise system for controlling dew points by using an active pressure control system in a primary standard humidity generator. By using this system, an adjustment capability to a target value of 0.0008 °C was attained for dew-point generation, compared with the previous value of approximately 0.01 °C. In a two-pressure humidity generator, the drift in the dew point with time owing to a rapid drop in the water level in the presaturator and to fluctuations in atmospheric pressure was greatly suppressed. The standard deviation of the dew point obtained with our dew-point control system was 10 times smaller than the drift observed in the absence of the system. This dew-point control system makes it possible to calibrate humidity sensors at target values with greater efficiency.