Uncertainty Analysis of Evaporation Rate in Magnetic Suspension Balance/Diffusion-Tube Humidity Generator

Abstract

An analysis method for the uncertainty of a small evaporation rate in a magnetic suspension balance/diffusion-tube humidity generator has been developed. Using experimentally obtained data, the uncertainty is evaluated as a function of measurement time. It is found that the observed standard deviation of the evaporation rate in a region of short measurement time (short term) is inversely proportional to the measurement time, and that in a region of long measurement time (long term) the standard deviation does not vary markedly with increasing measurement time. The behavior of the observed standard deviation in the short term is attributable mainly to the uncertainty of the balance reading, and that in the long term to the variability of room temperature. The results of the investigation show that the use of only least-squares analysis leads to underestimation of the uncertainty.

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

“…A similar experiment was performed as reported in [8], and the quantity value of c R estimated from the data was 0.20 °C(°C) −1 at a chamber temperature of 25 °C, more than twice that observed in this study. In [8], the tube connected to the inlet of the chamber was exposed to the atmosphere, whereas it was covered with a thermal insulator in this study. This suggests that the primary source of u g (q) is heat transfer from the outside through the dry nitrogen introduced into the chamber via the tube.…”

“…s(T G ) was obtained from measurement using the PRT and is a component of u(T). We found that the variability of the room temperature, T R , also affected the stability of the evaporation [8] and that s(T R ) is also a component of u(T). We thus obtain…”

“…Note that u e (q) cannot be evaluated using a single experimental data set. The evaluation of u e (q) is discussed in [8], in which it is denoted as u e (q f ).…”

“…The National Metrology Institute of Japan (NMIJ) previously developed a magnetic suspension balance/diffusiontube humidity generator (MSB/DTG) [4,[6][7][8][9] and started a calibration service for trace-moisture analyzers in the range of 12 nmol mol −1 -1.4 µmol mol −1 [4] on the basis of a primary trace-moisture standard realized using the MSB/DTG. In this article, we report full details of the uncertainty analysis performed on experimental data expressed in mole fractions and obtained using the 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.…”