Internal Measurement Assurance for the NIST Realization of the ITS-90 from 83.8 K to 1234.93 K

Abstract

The National Institute of Standards and Technology (NIST) is responsible for realizing, maintaining, and disseminating the International Temperature Scale of 1990 (ITS‐90) to the United States of America. The ITS‐90 fixed‐point cells necessary to calibrate standard platinum resistance thermometers (SPRTs) require an extensive internal measurement assurance program to insure that the assigned fixed‐point cell uncertainties are achieved. There are six interactive elements for the realization of an ITS‐90 fixed‐point cell that contribute to the uncertainty of an SPRT calibration. These six elements are the fixed‐point cells, furnace/maintenance systems, SPRT, measurement system, realization techniques, and measurement assurance. Within these six elements, there are twenty‐eight parameters that are used to quantify and maintain the NIST‐assigned fixed‐point cell and SPRT calibration uncertainties.