Realization of Radiance Temperature Scale from 500K to 1,250K by a Radiation Thermometer with a Thermal Detector

The radiance temperature scale from 500K to 1,250K was realized by using a thermal detector transfer reference thermometer (TRT) with its spectral response centered at 3.9μm. The TRT is calibrated at the four fixed points of tin, zinc, aluminum, and silver, and the scale is obtained by interpolation with Wien’s equation, Planck’s equation, the Sakuma–Hattori (SH) formula, and a Planckian SH (PSH) formula. The interpolation uncertainty dramatically decreases as the physical model for the interpolation equations becomes more realistic. The uncertainty of the scale is evaluated, including the repeatability of the calibration and the long-term stability of the TRT over a period of more than 20 months. The realized scale over part of the interpolation region was validated by comparing it with the ITS-90, resulting in excellent agreement within 0.09 K. The resulting uncertainty of the realized scale varies from 0.06K to 0.38K (k = 1), depending on the temperature.