Masaya Izuchi

Effects of Heat Treatment on the Inhomogeneity of the Pt/Pd Thermocouple at the Cu Freezing Point

The drift in emf of Pt/Pd thermocouples during successive calibrations at the Cu freezing point was measured. Twelve thermocouples were constructed using wires from a single lot, and a different heat treatment was performed on each thermocouple before the calibration. The purity of the Pt and Pd wires used were 99.999 % and 99.99+ %, respectively. The magnitude of the drift and the inhomogeneity of the thermocouples depended on the heat treatment. The heat treatment at 850 °C or 1030 °C for 100 h resulted in the minimum drift and inhomogeneity.

Uncertainty evaluation on the freezing point of silver for thermocouple calibration

The freezing point of silver is realized using an open type cell. The uncertainty of the thermocouple calibration of this temperature was evaluated using Pt/Pd thermocouples. The sources of uncertainty estimated were stability and repeatability of the plateau, temperature distribution in the cell. impurity effect of the metal, surroundings pressure correction and hydrostatic pressure correction. The combined standard uncertainty is 7.8 mK.

Uncertainty assessment on the calibration of Pt/Pd thermocouples at the freezing point of copper

For uncertainty assessment on the calibration of Pt/Pd thermocouples at the freezing point of copper, uncertainty components of the automatic ice point for the reference junction, the digital voltmeter, the thermocouple extension wires, and the copper wires were estimated. By combining these components and the others obtained elsewhere, the expanded uncertainty (k=2) was estimated to be approximately 0.11/spl deg/C.

EMF changes of Pt/Pd thermocouples at the Cu freezing point

The drift in EMF of Pt/Pd thermocouples during successive calibrations at the Cu freezing point was measured. The different heat treatment was performed to each thermocouple before the calibration. The magnitude of the drift of the thermocouples depended on the heat treatment. The heat treatment at 850/spl deg/C or 1030/spl deg/C for 100 hours resulted in reduction of the drift.

Effect of temperature distribution on EMF of thermocouples

A furnace was constructed to investigate the effect of temperature distribution on the EMF change caused by the inhomogeneity in each individual thermocouple. The EMF change of the inhomogeneous Pt/Pd thermocouple was observed by scanning the thermocouple in the temperature gradient region.

Uncertainty evaluation of the freezing point of aluminium for thermocouple calibration

The uncertainty of the freezing point of aluminium (660.323/spl deg/C) for thermocouple calibration was evaluated. The stability, the repeatability, temperature distribution along the thermometer well and the surroundings temperature were investigated as uncertainty components.

Thermoelectric properties of Pt/Pd thermocouples exposed to high temperature

The EMF values at Ag, Cu, Fe-C and Ni-C fixed points were measured with six Pt/Pd thermocouples constructed from a single lot of Pt and Pd wires, after being exposed to 1200/spl deg/C for 1000 hours in air. The drift of EMF at each fixed point has a tendency to increase slightly as the temperature of the fixed point is increased.