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The limits of a rayleigh scattering primary thermometer.

de Podesta, M; Edwards, G J (2008) The limits of a rayleigh scattering primary thermometer. Int. J. Thermophysics, 29 (5). pp. 1719-1729.

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We report progress in the development of an apparatus to compare the thermodynamic temperature of a gas with the temperature as determined by the International Temperature Scale of 1990 (ITS-90). The apparatus uses the Rayleigh scattering of light from a gas to provide an intensive measure of gas density, thus avoiding the need for corrections for dead volumes or wall adsorption required in conventional gas thermometry. A laser beam is shone through gas in two cells which are at the same pressure but different temperatures, and the measured ratio of the Rayleigh scattering signals from the two cells can be related to the ratio of the gas density in the cells. From the density ratio, the thermodynamic temperature of one cell can be inferred if the other cell is held close to the triple point of water. However, the Rayleigh scattering is weak and signals are small, making measurements with sufficiently small uncertainty extremely challenging. Since previous reports, the apparatus has been significantly modified and we describe these changes along with indicative results.

In this paper we present results of measurements in the range 211 K to 292 K using both argon and xenon. The results suffer from large systematic errors due to presence of contamination in one of the measurement cells. However, although the results do not provide reliable estimates of T -T90, they do indicate that the measurements with uncertainties below 1 mK are feasible.

Item Type: Article
Keywords: Gas thermometry, primary thermometry, Rayleigh Scattering
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4994

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