New primary dew-point generators at HMI/FSB-LPM in the range from -70°C to +60°C

To extend the dew-point range and to improve the uncertainties of the humidity scale realization at HMI/FSB-LPM, new primary low- and high-range dew-point generators were developed and implemented in cooperation with MIKES, in 2009 through EUROMET Project No. 912. The low-range saturator is designed for primary realization of the dew-point temperature scale from −70 °C to + 5 °C, while the high-range saturator covers the range from 1 °C to 60 °C. The system is designed as a single-pressure, single-pass dew-point generator. MIKES designed and constructed both the saturators to be implemented in dew-point calibration systems at LPM. The LPM took care of purchasing and adapting liquid baths, of implementing the temperature and pressure measurement equipment appropriate for use in the systems, and development of gas preparation and flow control systems as well as of the computer-based automated data acquisition. The principle and the design of the generator are described in detail and schematically depicted. The tests were performed at MIKES to investigate how close both the saturators are to an ideal saturator. Results of the tests show that both the saturators are efficient enough for a primary realization of the dew-point temperature scale from −70 °C to + 60 °C, in the specified flow-rate ranges. The estimated standard uncertainties due to the non-ideal saturation efficiency are between 0.02 °C and 0.05 °C.