Rusby, R; Pearce, J (2024) A further look at Type 1 non-uniqueness in the International Temperature Scale of 1990 above 273.16 K. AIP Conference Proceedings, 3230 (1). 080002

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Abstract

This paper is concerned with the sensitivity of Type 1 non-uniqueness (subrange inconsistency, SRI) to errors in the measurements of Standard Platinum Resistance Thermometers (SPRTs) at the fixed points of the International Temperature Scale of 1990, ITS-90, specifically on pairs of interpolations from the triple point of water (TPW, 273.16 K) up to the freezing points of zinc (FP Zn, 692.677 K) and aluminum (FP Al, 933.473 K). It follows on from a recent survey of SRI, which showed that propagation of uncertainty (error) could be responsible for much of the apparent SRI in the International Temperature Scale of 1990, ITS-90, using long-stem Standard Platinum Resistance Thermometers (L-SPRTs) above the triple point of water. The paper considers five possible sources of SRI, related to the definitions and specifications of the scale, the quality of the platinum wires, changes in the SPRT characteristics during calibration and the uncertainties of the measurements themselves. While some systematic offsets in the interpolations are caused by ‘scale-intrinsic’ SRI, it is clear that in most cases the two experimental sources dominate the SRI, as measured. It is suggested that the scale-intrinsic SRI, which is caused by the ITS-90 specifications rather than as an artefact of the calibration, is best estimated from the mean values of the SRI for groups of SPRTs, but that the standard deviations of historic data do not provide reliable estimates of extrinsic, SPRT-dependent SRI, because they themselves were predominantly due to similar measurement uncertainties, which should not be transmitted to subsequent budgets.

Item Type:	Article
Subjects:	Engineering Measurements > Thermal
Divisions:	Thermal & Radiometric Metrology
Identification number/DOI:	10.1063/5.0234213
Last Modified:	09 Jul 2025 15:00
URI:	https://eprintspublications.npl.co.uk/id/eprint/10200