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A Standardized Interpolation of Temperature using Rhodium-Iron Resistance Thermometers over the Interval 4.2 K to 24.5 K



Weston L. Tew, Richard Rusby, Peng Lin, Peter Steur, L. Lipinski, Barrie W. Ricketson


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() and a suitably reduced temperature . A reference function Zref() 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.
International Journal of Thermophysics


Interpolation, Rhodium-Iron Resistance Thermometers, Low Temperature, Thermometry


Tew, W. , Rusby, R. , Lin, P. , Steur, P. , Lipinski, L. and Ricketson, B. (2015), A Standardized Interpolation of Temperature using Rhodium-Iron Resistance Thermometers over the Interval 4.2 K to 24.5 K, International Journal of Thermophysics, [online], (Accessed June 24, 2024)


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Created April 30, 2015, Updated November 10, 2018