Design and validation of a new primary standard for calibration of the top-end humidity sensors

The article discusses the design and results of the initial testing of a primary single pressure dew-point generator, which is used for calibration of the top-end dew-point sensors and other types of humidity sensors. The dew-point generator operates in the dew/frost-point range from −60 °C up to +80 °C. The first experiments indicate that the expanded uncertainty of the generated dew/frost point is in the order of ±0.03 °C. Two saturators were designed and implemented in a single compact system. As the size of the saturators is quite large and the requirements to temperature gradients and stability of the saturators strict, special liquid baths were designed, which assures uncertainty due to temperature stability and uniformity below 2 mK. The dew-point generator was constructed to either work in single pass, partially recirculation or complete recirculation mode. This provides flexibility both when using the generator for calibration work but also when using the generator for experiments i.e. when evaluating the efficiency of the saturators. In order to achieve leak tight recirculation a new magnetically coupled pump has been developed. In this article, special attention is concentrated on the design of the saturators, the thermostats, and the pump.