Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Recent Results of NIST Realizations of the ITS-90 Below 84 K



Weston L. Tew, Christopher W. Meyer


The results at NIST of realizations and comparisons of the ITS-90 below 84 K are presented. The 3He and 4He vapor pressure scales (0.65 K to 5.0 K), and the interpolating constant volume gas thermometer (ICVGT) scale (5.0 K to 24.556 K) as realized from 1994 to 1996 are carried on a series of five check rhodium-iron resistance thermometers (RIRTs) which are periodically compared. The triple points of e-H2, Ne, O2, and Ar have been realized using a variety of cells and gas sources over the last six years. The resistance ratios of seven check capsule-type Standard Platinum Resistance Thermometers (SPRTs) at these triple points as well as the e-H2 vapor pressure points realized since 1994 are summarized. These check SPRTs are periodically compared with each other and with the check RIRTs. Comparisons of the NIST realizations as recorded on these RIRTs and SPRTs are presented. Comparison results compiled since 1997 are presented relative to those RIRT resistances and SPRT resistance ratios that were submitted by NIST for the Consultative Committee on Thermometry (CCT) Key Comparisons (KC-1 and KC-2). Data from some NIST triple-point realizations are compared to those from sealed triple point cells (STPCs) which were submitted by NIST to the PTB International Comparison of STPCs.
Temperature: Its Measurement and Control in Science and Industry


cryogenic temperatures, ITS-90, low temperature thermometry, RIRT, SPRT, temperature scale dissemination, temperature scale realizations, triple points, vapor pressure points


Tew, W. and Meyer, C. (2003), Recent Results of NIST Realizations of the ITS-90 Below 84 K, Temperature: Its Measurement and Control in Science and Industry, [online], (Accessed April 22, 2024)
Created January 1, 2003, Updated February 17, 2017