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NIST Realization of the ITS-90 Gallium Fixed Point



Gregory F. Strouse


As defined by the International Temperature Scale of 1990 (ITS-90), the gallium melting-point cell (29.7646 C) is used in the calibration of standard platinum resistance thermometers (SPRTs) for the ITS-90 subranges from 39 C to 30 C and from 0 C to 30 C. Different fixed-point cell designs and realization techniques were investigated to determine an optimum realization method and to determine if different cell designs and realization methods affect the reproducibility of the gallium triple-point (Ga TP) realization temperature. The results show that independent of cell design and mostly independent of gallium source, the range of the realization temperatures of 13 optimally realized Ga TP cells is 0.04 mK. This difference is well within the uncertainty (k=2) of 0.07 mK assigned to the NIST Ga TP reference cell. Additionally, improper realization techniques can increase uncertainties by an order of magnitude.
Proceedings Title
Conference Dates
August 1, 0007
Conference Title
NCSL International Workshop and Symposium


gallium, ITS-90, melting point, temperature, thermometric fixed point, thermometry, triple point


Strouse, G. (2005), NIST Realization of the ITS-90 Gallium Fixed Point, 2005 (Accessed July 21, 2024)


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Created August 1, 2005, Updated February 17, 2017