Uncertainty Assessment on the Freezing Point of Silver in the ITS-90

Abstract

The freezing point of silver, one of the temperature fixed points defined in the ITS-90, is realized using an open type cell. The uncertainty in realizing the freezing point was assessed. The sources of uncertainty estimated were repeatability, self-heating correction, surroundings pressure correction, hydrostatic pressure correction, surroundings temperature correction, temperature distribution in the cell and impurity effect of the metal. The combination of those sources of uncertainty gives a combined standard uncertainty of 1.39mK. The uncertainty coming from the impurity effect of the metal, 1.29mK, was found to be the largest source.