Standard Test Method for Calibration of Refractory Metal Thermocouples Using a Radiation Thermometer

Importancia y uso:

5.1 This test method is intended to be used by wire producers and thermocouple manufacturers for certification of refractory metal thermocouples. It is intended to provide a consistent method for calibration of refractory metal thermocouples referenced to a calibrated radiation thermometer. Uncertainty in calibration and operation of the radiation thermometer, and proper construction and use of the test furnace are of primary importance.

5.2 Calibration establishes the temperature-emf relationship for a particular thermocouple under a specific temperature and chemical environment. However, during high temperature calibration or application at elevated temperatures in vacuum, oxidizing, reducing or contaminating environments, and depending on temperature distribution, local irreversible changes may occur in the Seebeck Coefficient of one or both thermoelements. If the introduced inhomogeneities are significant, the emf from the thermocouple will depend on the distribution of temperature between the measuring and reference junctions.

5.3 At high temperatures, the accuracy of refractory metal thermocouples may be limited by electrical shunting errors through the ceramic insulators of the thermocouple assembly. This effect may be reduced by careful choice of the insulator material, but above approximately 2100 °C, the electrical shunting errors may be significant even for the best insulators available.

Subcomité:

E20.11

Referida por:

E0696-23, E0220-19, E0344-23, E0220-19

Volúmen:

14.03

Número ICS:

17.200.20 (Temperature-measuring instruments)

Palabras clave:

high-temperature calibration; optical pyrometer; radiation thermometer; refractory metal thermocouple; thermocouple; thermocouple calibration; vacuum furnace ;