Performance investigation of blackbody BB3 500 M and temperature measurement

High temperature blackbody BB 3 500 M was used as the primary standard of spectral irradiance at national institute of metrology (NIM). The blackbody BB 3 500 M cavity radiator was consisted of a series of pyrolytic-graphite (PG) rings, capable of operating at temperature up to 3 500 K. Feedback control mode was used to stabilize the temperature of the blackbody. The stability of the radiator and the blackbody uniformity were measured. In transferring the spectral irradiance from the blackbody to the working standard lamp, the temperature of the blackbody may change. In the experiment, temperature drift within an hour was tested. When the blackbody was heated up to around 3 016 K, the temperature uncertainty was less than 0.3 K. In the radiation path, an aperture was used to screen the radiation from the cylindrical part of the radiation cavity. However, the temperature was not the same all over the effective area of the graphite bottom. The uniformity of the bottom of BB 3 500 M was found to be within 0.2 K. Results showed that BB 3 500 M was suitable for the primary radiation source. In the temperature measurement, temperature below 2 473 K could be traceable to the heat division of NIM. Then the temperature could be extended through the comparison of the spectral radiance at fixed wavelength. In the experiment, the temperature extend was first investigated in low temperature region no higher than 2 473 to verify its applicability. Results in high temperature region showed good consistence that the temperature divergence was smaller than 0.5 K at 345 nm～360 nm wavelength.