Non-Uniquenes of the ITS-90 From 13.8033 K to 24.5561 K

Published

June 1, 1999

Author(s)

Christopher W. Meyer, Gregory F. Strouse, Weston L. Tew

Abstract

The International Temperature Scale of 1990 (ITS-90) is defined in the region 3.0 K to 24.5561 K by an interpolating constant volume gas thermometer (ICVGT) that is calibrated at three specified fixed points. From 13.8033 K to 1234.93 K the ITS-90 is defined by means of a standard platinum resistance thermometer (SPRT) calibrated at several specified fixed points. Two of the SPRT fixed points (at 17.035 K and 20.27 K) may be realized by using either of two different types of thermometry. Therefore, from 13.8033 K to 24.5561 K the possibility exists for non-uniqueness in the ITS-90 due to the overlap of three equally valid definitions (one CVGT and two SPRT) that do not necessarily agree. An apparatus for realizing the ITS-90 below 85 K has been constructed at the National Institute of Standards and Technology. The apparatus includes an ICVGT that uses 4He as the working gas and cells for realizing the fixed points used to calibrate an ICVGT and an SPRT below 85 K. We present here a determination of the non-uniqueness of the ITS-90 from 13.8033 K to 24.5561 K by means of direct comparisons between temperatures realized by the three valid definitions.

Citation

Symposium on Temperature and Thermal Measurement in Industry and Science

Pub Type

Journals

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Keywords

calibration, gas thermometry, ITS-90, platinum resistance thermometry, temperature scale, vapor-pressure thermomet

Citation

Meyer, C. , Strouse, G. and Tew, W. (1999), Non-Uniquenes of the ITS-90 From 13.8033 K to 24.5561 K, Symposium on Temperature and Thermal Measurement in Industry and Science, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=830632 (Accessed October 13, 2025)