Tew, W L*; Rusby, R L; Lin, P*; Lipinski, L*; Steur, P P M*; Ricketson, B W A* (2015) A standardized interpolation of temperature using rhodium-iron resistance thermometers over the interval 4.2 K to 24.5 K. Int. J. Thermophysics, 36 (8). pp. 2036-2059.

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Abstract

The worldwide history and current state of development of rhodium-iron resistance thermometers (RIRTs) is briefly reviewed. A standardized interpolation method using RIRTs with the nominal composition of 0.5 % Fe (by mole) is presented, with examples using data taken from 60 RIRTs made from a variety of wire batches and sources worldwide over the last 40 years. The parameterization exploits the favourable characteristics of the Cragoe reduced resistance Z(t) and a suitably reduced temperature t. A reference function Zref(t) which approximates the average characteristics of selected wire is derived for use over the interval 0.65 K to 24.5561 K on the ITS-90. We examine the deviations of real RIRT data from this reference function and present simple 4-parameter Fourier-series solutions for the resulting deviation curves. Despite the fact that the wire samples may be of different origins or state-of-anneal, we find that the interpolations are successful for most of the samples studied over the 4.2 K to 24.5561 K interval, at the level of ~1 mK uncertainty or less. This method would allow for calibrations of most RIRTs over this interval using only six calibration points, permitting an efficiency not achievable using the common least-square curve-fitting calibration methods. The potential of this formalism for a standardized interpolation scheme using RIRTs is discussed.

Item Type:	Article
Keywords:	Interpolation, RIRT, Low Temperature, Thermometry
Subjects:	Engineering Measurements Engineering Measurements > Thermal
Identification number/DOI:	10.1007/s10765-015-1877-4
Last Modified:	02 Feb 2018 13:13
URI:	http://eprintspublications.npl.co.uk/id/eprint/6820

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