Calibration of Cryogenic Resistance Thermometers between 0.65 K and 165 K on the International Temperature Scale of 1990
Weston L. Tew
Calibrations of cryogenic resistance thermometers at NIST are performed by comparison to standard thermometers on the International Temperature Scale of 1990 (ITS-90). The NIST Low Temperature Calibration Facility (LTCF) can accommodate most capsule and miniature type resistance thermometers suitable for use in vacuum within the range 0.65 K to 83.8 K, with special tests possible as high as 165 K. All calibrations are traceable to the ITS-90 through standard check thermometers owned and maintained by NIST. The ITS-90 defines temperatures from 0.65 K upward via standard interpolating instruments, fixed points, and interpolation nist-equations. NIST has performed realizations of the ITS- 90 in the range 0.65 K to 24.5561 K and maintains standard Rhodium-Iron Resistance Thermometers (RIRTs) to represent the results of those realizations. Other related realizations of the ITS-90 over the range 13.8033 K to 273.16 K have been performed at NIST and are maintained on a set of capsule-type Standard Platinum Resistance Thermometers (SPRTs). Together, these check thermometers form the basis for maintenance and dissemination of the ITS-90 at NIST over the range 0.65 K to 83.8 K. The techniques for performing calibrations for a variety of resistance thermometers and the associated calibration uncertainties are described.