Radiation temperature scales between the indium and silver points realized at IMGC, NPL and UME using a fixed-point calibration technique

Radiation temperature scales were realized with a precision infrared thermometer at IMGC, NPL and UME using fixed-point blackbodies at the freezing points of indium, tin, zinc, aluminium and silver. From the fixed-point calibration in each laboratory, continuous scales were obtained with a four-coefficient interpolation equation. The differences between the three scales were well within 0.1 degreesC at all temperatures between the indium and silver points. Calibrations of the same thermometer performed at NPL and UME using a more traditional calibration scheme based on the comparison with contact thermometers showed differences of up to more than 0.4 degreesC. This suggested that the fixed-point scheme, that has been used for the first time in an international comparison, should be more reliable for accurate calibrations of precision infrared thermometers.