A European research project METefnet addresses a fundamental obstacle to improving energy intensive drying process control: due to ambiguous reference analysis methods and insufficient methods for estimating uncertainty in moisture measurements, the achievable accuracy in the past was limited and measurement uncertainties were largely unknown. This paper reports the developments in METefnet that provide a sound basis for the SI traceability: four new primary standards for realising the water mass fraction were set up, analysed and compared to each other. The operation of these standards is based on combining sample weighing with different water vapour detection techniques; cold trap, chilled mirror, electrolytic and coulometric Karl Fischer titration. The results show that an equivalence of 0.2 % has been achieved between the water mass fraction realisations and that the developed methods are applicable to wide range of materials.
The aim of this paper is to describe a bilateral comparison carried out by the hygrometry laboratories of the National Metrological Institutes of Brazil and Argentina, INMETRO and INTI, respectively. This comparison was planned and carried out as an informal comparison. But, in view of the lack of and the need for humidity comparison reports in the region of the Inter American Metrology System (SIM), we decided to register this comparison as a bilateral key comparison of the regional metrology organization (RMO), SIM.T-K6.4–INMETRO/INTI. The comparison was performed in the range from −20 ºC to +60 ºC dew/frost point temperatures in 20 °C steps. This paper presents the calibration methods of the laboratories, the uncertainty analysis and the comparison results. The measurements results of the comparison are also presented in terms of the normalised error (En) as a function of the dew/frost point temperature.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).
Main text This report presents the results of a comparison in the context of an international collaboration that gives confidence in the relative humidity measurements carried out by several Latin-American institutes within the Mutual Recognition Arrangement (MRA) of the International Committee on Weights and Measures (CIPM). This interlaboratory comparison of humidity standards, the first one in Latin-America and one of the few of this type in the world, was organized in two rounds and carried out by the following National Metrology Institutes: INMETRO (Brazil), IBMETRO (Bolivia), INEN (Ecuador), INM (Colombia), CENAMEP AIP (Panama), ENAER (Chile), INTI (Argentina), LATU (Uruguay) and INTN (Paraguay). The interlaboratory comparison was performed in the scope of relative humidity in the range from 30 %rh to 90 %rh at temperatures of 20 °C and 40 °C. In this comparison, INMETRO was the reference laboratory, and acted as coordinator together with IBMETRO. Two thermohygrometers with capacitive humidity sensors were used as transfer standards, which were calibrated three times by the reference laboratory during the course of the interlaboratory comparison. A technical protocol prepared by INMETRO and IBMETRO circulated among the participants for comments. To sum up, the participants used their own calibration procedures for calibrating the transfer standards together with some instructions given in the technical protocol. Besides, the participants had to submit with the measurement results the respective uncertainties estimated according to their internal procedures and the Guide to the Expression of Uncertainty in Measurement (GUM). The performance of each participating laboratory was evaluated by comparing its measurements results with those of the reference laboratory by means of the normalized error, according to ISO/IEC 17043:2010, and by the degree of equivalence. 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 https://www.bipm.org/kcdb/. 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).
Two methods for the uncertainty estimation in the dew/frost-point temperature and relative humidity are shown. The uncertainty estimation was performed propagating the uncertainties of pressure and temperature measurements in the corresponding equations in the classic method, and propagating the distributions of the input variables, pressure and temperature, (Monte Carlo simulation) in an alternative method. The results obtained by the different methods are compared for analyzing the validity of the uncertainty calculations, and the assumption of negligible correlations between the input variables. The agreement between the presented uncertainty analysis and the outcomes of the comparison with INMETRO is discussed. List of symbolsrh Relative humidity t dew Dew-point temperature t frost Frost-point temperature e w (t) Vapor pressure f (t, P) Enhancement factor P s Total pressure in saturator P c Total pressure in test chamber t s Temperature in saturator t c Temperature in test chamber 123 Int J Thermophys u(rh) Standard uncertainty in relative humidity u(t dew ) Standard uncertainty in dew-point temperature u(t frost ) Standard uncertainty in frost-point temperature u(e w ) Standard uncertainty in vapor pressure equation u( f ) Standard uncertainty in enhancement factor equation u(P s ) Standard uncertainty of saturation pressure measurement u(P c )Standard uncertainty of chamber pressure measurement u(t s ) Standard uncertainty of saturation temperature measurement u(t c )Standard uncertainty of chamber temperature measurement
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