SPECIAL REPORT ON THE INTERNATIONAL TEMPERATURE SCALE OF 1990 - REPORT ON THE 17TH SESSION OF THE CONSULTATIVE COMMITTEE ON THERMOMETRY

This article summarizes the results of the 17th Session of the Consultative Committee on Thermometry of the International Committee of Weights and Measures that met in Sevres, France, September 12-14 1989. That session was devoted exclusively to the completion of the International Temperature Scale of 1990, described herein, and to the implications of its adoption. Although the uncertainties in the values of thermodynamic temperatures above 100°C used in the definition of the ITS-90 were larger than desired and larger than had been anticipated a few years ago, the agreement of temperatures on the ITS-90 with thermodynamic temperatures is nevertheless a significant improvement over that of previous scales. The replacement of the thermocouple with the platinum resistance thermometer as the standard instrument of the scale at temperatures in the IPTS-68(75) range from 630.74 to 961.93°C has improved the reproducibility over that of the IPTS-68(75) significantly. Also, advances in radiometric techniques have improved the precision of measurements in radiation thermometry.