Extension of dew-point temperature scale has been performed using a two-temperature (2-T), constant pressure humidity generator that is developed for the first time by the National Institute of Standard (NIS) in order to extend the calibration capabilities to the high dew-point temperature range at NIS. It relies on the saturation of a stream of gas flowing over a water surface maintained at constant, well-known, temperature. In this paper, primary realization of dew-point temperature scale in a dew-point temperature range up to +50 °C was performed to extend calibration capabilities and to improve the uncertainties of the dew-point temperature scale realization. Several experiments were carried out in order to characterize the generator. Characterization comprises studies of the saturator efficiency, temperature stability and a comparison with a calibrated chilled-mirror hygrometer. The results of the efficiency tests showed good performance of the generator. For uncertainty of measurements, a thorough analysis was also described representing estimations of contributions for all the sources that possibly affect measurements.
Extending dew-point temperature scale up to +50 °C