Densimetry for Primary Temperature Metrology and a Method for the In-situ Determination of Densimeter Sinker Volumes
Mark O. McLinden
The feasibility of using gas-phase pressure-density-temperature (p-ρ-T) measurements as a method of determining thermodynamic temperatures is evaluated. Densities are measured at the unknown and reference temperatures at identical pressures, and the resulting density ratios are extrapolated to zero pressure to yield the ratio of the temperatures. The method utilizes a two-sinker densimeter with a magnetic suspension coupling to separate the sinkers (in the working gas) from the balance (in atmosphere). Numerical studies investigate the optimum working gas and the effects of experimental uncertainties on the uncertainty in temperature. The method is demonstrated using an existing densimeter over the range of 234 K to 505 K with argon, nitrogen, and neon as the working gas. Experimental protocols and data analysis techniques are developed. The technique is shown to be feasible, although the present densimeter has uncertainties which are too high for temperature metrology. In particular, the uncertainty in the sinker volumes is relatively large. The method is inverted to determine, in-situ, the sinker volumes as a function of temperature, reducing their uncertainties, and thus the uncertainties of fluid densities measured with this apparatus, by a factor of two compared to values computed using sinker volumes computed using thermal expansivities.
density, gas thermometer, temperature, two-sinker densimeter, volume
Densimetry for Primary Temperature Metrology and a Method for the In-situ Determination of Densimeter Sinker Volumes, Measurement Science & Technology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50305
(Accessed November 30, 2023)