Abstract
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.
Highlights
There are several techniques used to generate humidity references by using stream of saturated gas with wellknown water vapor content to be used in calibration of chilled-mirror hygrometers such as two-pressure humidity generator, one-temperature dew-point temperature scale, and two-temperature humidity generator [1,2,3]
The results showed good performance for the generator complying with the concerned range and a measurement expanded uncertainties ranging from ±0.065 °C to ±0.074 °C at dew-point temperatures of 0 to À40 °C, respectively [4]
The obtained results from measurements of the saturator system is given in the temperature range from À10 to +50 °C, increasing by +10 °C (i.e., À10, 0, +10, +20, +30, +40, +50 °C), showing a temperature stability in the dewpoint temperate range
Summary
There are several techniques used to generate humidity references by using stream of saturated gas with wellknown water vapor content to be used in calibration of chilled-mirror hygrometers such as two-pressure humidity generator, one-temperature dew-point temperature scale, and two-temperature humidity generator [1,2,3]. NIS primary two-temperature (2-T) humidity generator was previously developed and characterized in the dew-point temperature range from À50 to +10 °C. Characterization of the generator and efficiency tests were carried out through studies on the temperature stability of its liquid bath and the variation of air flow rate at a different temperature in the dew-point range from À50 to +10 °C. The results showed good performance for the generator complying with the concerned range and a measurement expanded uncertainties ranging from ±0.065 °C to ±0.074 °C at dew-point temperatures of 0 to À40 °C, respectively [4]. This work describes the realization of the dew-point temperature scale in the range from À10 to +50 °C using (2-T) humidity generator for the first time at NIS to extend the calibration capabilities to the high dew-point range. Dew-point temperature above ambient temperature should be measured with special provisions; the dew-point meter
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