A comparison of the In, Sn, Zn and Al fixed points by radiation thermometry between NIM and NPL and verification of the NPL blackbody reference sources from 156 °C to 1000 °C

National Institute of Metrology, China (NIM) and National Physical Laboratory, UK (NPL) blackbody cavities based on the ITS-90 freezing points of In, Sn, Zn and Al have been compared by radiation thermometry. The average differences between In, Sn and Zn, measured by NPL InGaAs radiation thermometer, are 5.3, 2.2 and -7.3 mK, respectively, and the average differences between Sn, Zn and Al, measured by NIM InGaAs radiation thermometer, are 1.4, -5.8 and 13.7 mK, respectively. These differences are well within the uncertainties of the comparison. The NPL blackbody reference sources from 156 degrees C to 1000 degrees C were verified using both the NPL and the NIM InGaAs thermometers calibrated at the fixed points. The differences between the radiance temperature of the sources and the temperature measured by the contact sensor within the source are generally within 0.1 K.