INVESTIGATION OF THE NON-UNIQUENESS OF THE ITS-90 IN THE RANGE 660°C TO 962°C

摘要

Preliminary results are reported on the non-uniqueness of the ITS-90 using high temperature SPRTs (HTSPRTs) in the range 660°C to 962°C. To achieve temperature stability and uniformity of the test HTSPRTs, the method employs the thermal isolation of the Inconel metal comparison block inside a sealed potassium heat pipe controlled to +-0.01 K. Eleven HTSPRTs of three designs from five manufacturers were tested. In addition to measurements near the calibration temperatures 663.3°C and 966.6°C to test the temperature uniformity of the comparison block, measurements were made at 703.3°C, 724.4°C, 753.2°C, 801.7°C, 847.5°C, and 913.7°C.