Recent Advances in the Realization and Dissemination of the ITS-90 Below 83.8058 K at NIST
Recent advances in our knowledge of the International Temperature Scale of 1990 (ITS-90), as realized and maintained at the National Institute of Standards and Technology (NIST), are briefly reviewed. As a result of these advances, the NIST disseminated version of ITS-90 has recently undergone small adjustments below 83.8058 K. These adjustments are all at the sub-millikelvin level and reflect the inclusion of recent data on ITS-90 realizations and intercomparisons of reference thermometers. Specifically, developments in the realization of ITS-90 fixed points, gas thermometry, and vapor pressure thermometry at NIST have significantly improved our knowledge of scale non-uniqueness and dissemination uncertainty in the lowest temperature ranges. We briefly describe the present status of ITS-90 realizations at NIST and which definitions are currently being disseminated. Our procedures for calibration of standard reference thermometers for cryogenic use are reviewed and our updated assessments of calibration uncertainties are presented. These include calibration of Standard Platinum Resistance Thermometers (SPRTs) of the capsule type between 13.8033 K and 273.16 K, and of Rhodium-Iron Resistance Thermometers (RIRTs) between 0.65 K and 83.8058 K. In addition, we preview a new Standard Reference Material® (SRM®) project which will make available “as defined” ITS-90 calibrated capsule SPRTs through the MST SRM program. These continuing advances in scale realization and dissemination at NIST will improve the accuracy and availability of ITS-90 standards throughout the cryogenic engineering community.
KeywordsTriple Point Calibration Uncertainty Standard Platinum Resistance Thermometer International Temperature Scale American Institute ofPhysics
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