Thermodynamic temperature measurements of Al–Cu, Al, Ag, Cu and Co–C fixed points by radiometry hybrid method

Abstract The radiometry hybrid method, by introducing a lens to the irradiance method with a 900 nm filter radiometer, was adopted to measure the thermodynamic temperature of the aluminum-copper (Al–Cu) eutectic point, aluminum (Al) freezing point, silver (Ag) freezing point, copper (Cu) freezing point and cobalt carbon (Co–C) eutectic point at the National Institute of Metrology, China. By scanning the uniformity of fixed-point blackbodies, the effective diameters were accurately estimated according to the size of the source effect (SSE). The lens transmittance measurement with the closest diameter aperture was adjusted to reduce the uncertainty of SSE. The discrepancy between the thermodynamic temperature and ITS-90 values ( T-T 90 ) of Al–Cu, Al, Ag, Cu and Co–C fixed point blackbodies were concluded as 0.022 °C, 0.014 °C, 0.097 °C, 0.137 °C and 0.317 °C, respectively. The standard uncertainty of the fixed point thermodynamic temperature was estimated to be (0.1 to 0.3) °C ( k = 2).