Low-Pressure and Low-Temperature Dew/Frost-Point Generator

Lately demands for traceability and improved accuracy in climatic humidity measurements at extreme conditions have been increasing. To address these needs a new dew/frost-point generator was developed and constructed at the Centre for Metrology MIKES of the VTT Technical Research Centre of Finland Ltd. for the range from − 90 °C to + 15 °C. The generator operates in a single-pressure principle at the absolute air pressure range from 10 hPa to 3500 hPa. With an expansion valve it can be applied also in two-pressure mode. Within this paper the new low-pressure and low-temperature dew/frost-point generator and its characterization are presented in detail. The outcomes of the characterization show that when operating in a single-pressure mode within barometric pressure range a standard uncertainty of 0.043 °C is achieved in complete temperature range. When considering the complete pressure range the standard uncertainty is larger, but it does not exceed 0.06 °C.