Development of the High-Temperature Dew-Point Generator Over the Past 15 Years

Abstract

At VSL a humidity generator was designed and constructed in the early 1990s. This generator was of the re-circulating-single-pressure type. Over the years, the generator has been thoroughly revised and several critical components have been replaced. Among others the pre-saturator and the change from re-circulation to single-pass mode. Validating experiments showed that the range of the new setup could be extended from $70\,{^{\circ }}\hbox {C}$ to $95\,{^{\circ }}\hbox {C}$ dew-point temperature, and the last modification allows an uncertainty of $0.048\,{^{\circ }}\hbox {C}$ (k = 2) at the maximum temperature. In 2009 the setup was used in the Euramet-T-K8 humidity intercomparison at temperatures up to $95\,{^{\circ }}\hbox {C}$. In the period from 2003 to 2015, four state-of-the-art chilled mirror hygrometers were regularly calibrated with the generator. One of these was also calibrated with the primary dew-point standards of several other European National Metrology Institutes, which made it possible to link the VSL generator to the generators used in these institutes. An analysis of the results of these calibrations shows an agreement in calibration capabilities within $0.01\,{^{\circ }}\hbox {C}$ with PTB and NPL.