Final report on CCT-K6: Comparison of local realisations of dew-point temperature scales in the range −50 °C to +20 °C

Abstract

A key comparison in dew-point temperature was carried out among the national standards held by NPL (pilot), NMIJ, INTA, VSL, INRIM, MIKES, NIST, NIM, VNIIFTRI-ESB and NMC. A pair of condensation-principle dew-point hygrometers was circulated and used to compare the local realisations of dew point for participant humidity generators in the range −50 °C to +20 °C. The duration of the comparison was prolonged by numerous problems with the hygrometers, requiring some repairs, and several additional check measurements by the pilot. Despite the problems and the extended timescale, the comparison was effective in providing evidence of equivalence. Agreement with the key comparison reference value was achieved in the majority of cases, and bilateral degrees of equivalence are also reported.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Bilateral key comparison SIM.T-K6.5 on humidity standards in the dew/frost-point temperature range from -30 °C to +20 °C

“…Here, e ( T DP/FP )= e w ( T DP ) for T DP/FP ≥ 0, where e w is the saturated vapor pressure for water, calculated using [1–2]. Also, e ( T DP/FP )= e i ( T FP ) for T DP/FP < 0, where e i is the saturated vapor pressure for ice, calculated using [5–6].…”

“…Because NIST participated in the CCT-K6 multilateral key comparison, some of the results of this bilateral comparison may be linked to the key comparison reference value (KCRV) for T DP/FP [1]. The degree of equivalence between T DP/FP realized by a NMI and the KCRV, D NMI/KCRV , is defined as $$D_{\text{NMI/KCRV}}false(T_{\text{DP/FP}}false)\equiv {\left[\mathrm{\Delta }{T}_{\text{DP/FP}}\right]}_{\text{NMI}}-{\left[\mathrm{\Delta }{T}_{\text{DP/FP}}\right]}_{\text{KCRV}}.$$…”

“…The National Institute of Standards and Technology (NIST, USA) participated in this key comparison. The comparison report was recently published [1]. …”

Bilateral key comparison SIM.T-K6.2 on humidity standards in the dew/frost-point temperature range from -20 °c to 20 °c

“…For T DP/FP ≥ −15 °C, the HHG operates as a conventional two-pressure generator, saturating air with water at a temperature T s and pressure P s to produce moist air with a molar fraction x g given by 1) Here, e(T s ) is the water vapor pressure at T s, calculated using [2][3] and f(T s , P s ) is the watervapor enhancement factor, calculated using [4]. The saturator temperature is measured by a standard platinum resistance thermometer (SPRT) immersed in the same temperaturecontrolled bath as the saturator.…”

“…Because NIST participated in the CCT-K6 multilateral key comparison, some of the results of this bilateral comparison may be linked to the key comparison reference value (KCRV) for T DP/FP [1]. The degree of equivalence between T DP/FP realized by a NMI and the KCRV,D NMI/KCRV , is defined as…”