Uncertainty analysis for trace-moisture standard realized using a magnetic suspension balance/diffusion-tube humidity generator developed at NMIJ

Abstract

A method of estimating the uncertainty for a primary trace-moisture standard realized using a magnetic suspension balance/diffusion-tube humidity generator (MSB/DTG) developed at the National Metrology Institute of Japan (NMIJ) is reported in full detail. The results of uncertainty analysis showed that the relative expanded uncertainties of the trace-moisture standard with a coverage factor of k = 2 are 6.9 % to 0.75 % for the amountof-substance fractions (mole fractions) of water in nitrogen in the range of 12 nmol mol −1 to 1400 nmol mol −1 . NMIJ participated in an international comparison of primary trace-moisture standards, and the results of the comparison demonstrated that the method of estimating uncertainty developed in this study is reasonable. The dominant uncertainty was attributable to the performance of the trace-moisture analyzer used to evaluate the uncertainty. We conclude that the development of a trace-moisture analyzer based on cavity ring-down spectroscopy with higher performance is needed to reduce the uncertainty of trace-moisture standards based on an MSB/DTG.

Trace-moisture measurement using cavity ring-down spectroscopy at NMIJ

“…NMIJ developed three trace-moisture generators using the diffusion method [7,[27][28][29][30][31][32][33]. In this section, the magnetic-suspensionbalance/diffusion-humity genertor (MSB/DTG), which was the first generator developed at NMIJ is briefly presented.…”

“…The standard uncertainty [35] of the trace-moisture standard realized using the MSB/DTG at the NMIJ evaluated, as summarized in Table 1 [31]. An international comparison of primary trace-moisture standards established by NMIs was organized by the European Association of National Metrology Institutes (EURAMET), and NMIJ participated in this comparison [8].…”

Gas dilution system using critical flow Venturi nozzles for generating primary trace-moisture standards in multiple gas species

“…This was because the derivative of the discharge coefficient with respect to P u at 84 kPa for Q 3 is six times greater than that at 612 kPa for Q 2 ; therefore, Q 3 was more susceptible to fluctuations in P u than Q 2 . This can also be explained using equations ( 5)- (10): equation (5) shows that Q m is proportional to C d . Equation (7) indicates that C d becomes more susceptible to change in Re Th as Re Th decreases.…”

“…Performance testing or calibration based on experiments traceable to the International System of Units (SI) is essential for reliable measurement, but is impossible to practice without primary standards. The National Metrology Institute of Japan (NMIJ) established a primary trace-moisture standard in N 2 [3][4][5]. NMIJ tested the performance of some commercial measuring instruments on the basis of the trace-moisture standard and found that those measuring instruments do not have a sufficient measurement capability in the range below 100 nmol mol −1 [4], despite manufacturers' performance claims.…”

“…We previously developed a two-stage dilution system for a secondary trace-moisture standard in N 2 using thermal mass flow controllers (MFCs) to control the flow rates of the gas [8]. The measured values of the flow rates were not used to calculate the standard values of trace moisture, because the standard values were determined from the values measured using a trace-moisture analyzer calibrated against the primary trace-moisture standard in N 2 that had been developed at NMIJ [3][4][5]. For a primary trace-moisture standard, in contrast to a secondary trace-moisture standard, the standard values must be determined from the measured values of the flow rates, requiring high accuracy of flow measurement.…”