Middle temperature scale for infrared radiation thermometer calibrated against multiple fixed points

The NMIJ has established a temperature scale for infrared radiation thermometry from 100 to 420 degrees C consisting of three fixed-point blackbodies at the In, Sn, and Zn points and an InSb detector thermometer at a wavelength of 4.7 mu m. The blackbody cavities have large openings of 15 mm diameter. The expanded uncertainties (k = 2) of the In, Sn, and Zn fixed-point radiance temperatures are estimated to be 0.03, 0.03, and 0.05 K, respectively. The expanded uncertainties (k = 2) for the calibration of the infrared radiation thermometer are estimated to be 0.04 K at 157 degrees C (In point), 0.04 K at 232 degrees C (Sn point), and 0.07 K at 420 degrees C (Zn point).