New interpolating equations of ITS-90 for SPRTs and HTSPRTs for the temperature range 419.527 °C–961.78 °C. (26th June 2020)

• Record Type: Journal Article
• Authors: Sun, J P; Li, T; P Hao, X; Pan, J; X Zeng, J
• Is Part Of: Metrologia. Volume 57:Number 4(2020:Aug.)
• Publication Date: 2020-06-26
• Subjects: ITS-90 -- inconsistency -- SPRT -- fixed point -- interpolating equation; Weights and measures -- Periodicals; Weights and Measures -- Periodicals; 530.805
• DOI: 10.1088/1681-7575/ab8828
• Languages: English
• ISSNs: 0026-1394

Abstract

Abstract: The subrange inconsistency (SRI) of the International Temperature Scale of 1990 (ITS-90) arises from the use of different interpolating equations for the same standard platinum resistance thermometers (SPRTs), called Type 1 non-uniqueness, and is a significant component of the uncertainty in the realization of the scale. In order to eliminate the SRI, new interpolating equations were proposed for the subranges 0.01 ° C to 660.323 ° C and 0.01 ° C to 961.78 ° C, in which the subrange to the zinc point (419.527 ° C) was extended using two additional terms without any overlap. This study investigated 30 SPRTs calibrated over the temperature range of 0.01 ° C–660.323 ° C and 19 high-temperature SPRTs (HTSPRTs) calibrated over 0.01 ° C–961.78 ° C at the National Institute of Metrology (NIM). The feasibility of the proposed equations were evaluated by comparing them with the equations defined in ITS-90 and calculating the propagation uncertainties. The results show that the differences between the defined interpolating equations in ITS-90 and the proposed interpolating equations are generally within ± 0.4 mK for temperature range of 419.527 ° C–961.78 ° C, which is close to or less than the SRIs between the water-zinc and water-aluminium subranges. The propagated uncertainties of the proposed equations were within reasonable limits. It is concluded that these new interpolating equations can be taken as equivalent to the ITS-90 interpolating equations with the SRI eliminated.