Low-cost use of metal freezing-points in the 30–250 °C range for calibration: On-site application of standards-defining methodology

This paper investigates the potential for using the freezing-points of high-purity metals for direct temperature calibration, on site and at low cost. These freezing-points are primary calibration points in the International Temperature Scale (ITS-90). It has been found that small amounts of high-purity metals can be obtained in the marketplace cheaply. Experiments were carried out by driving a constant current through a resistance temperature detector (RTD) immersed in a sample of a pure metal and measuring the voltage across it as it transited from liquid to solid. The voltage was found to be constant for a time, as expected, due to the release of latent heat by the metal as it froze, keeping the temperature constant. These voltage values can then be equated to the temperature of the metal´s freezing-point.