A comparison of PRTs at the Cu–Ag eutectic point (780 °C)

Abstract

Twelve platinum resistance thermometers (PRTs) were repeatedly calibrated between the triple point of water and the silver point. During each calibration their resistance was also determined at the Cu–Ag eutectic point. The temperatures indicated by the PRTs were within ±1 mK, except for one that differed by 4 mK from the average, 779.6360 °C, of the other eleven.Four of these PRTs had a lower W (Ag) value than acceptable by the ITS-90, including the one that differed by 4 mK. Thus, within this set of PRTs all the ‘acceptable’ ones and three out of four ‘unacceptable’ ones indicated a unique temperature within 1 mK halfway between the aluminium and the silver points.