TEMPERATURE DETERMINATION OF THE AG- AND AU-FREEZING POINTS USING A DETECTOR-BASED RADIATION THERMOMETER

摘要

We describe the development and the characterization of a radiation thermometer calibrated using detector-based radiometry to determine the thermodynamic temperatures of the Ag- and Au-freezing temperatures. The radiometer utilizes an on-axis design with lenses with f/13 collection optics for imaging a 0.75 mm target area. The radiometer utilizes an interference filter with the center wavelengths at 650 nm for at least 10"8 suppression of the spectral responsivity in the out-of-band region to 1100 nm. The absolute spectral radiance responsivity of the radiation thermometer is measured in the NIST Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (SIRCUS) facility with a total uncertainty of 0.15 % (k=2). The size-of-source effect (SSE) is determined using a light-emitting diode illuminated radiance source, and the linearity of the thermometer is characterized using 0.01 % precision resistors. With the corrections for SSE, linearity and emissivity of the blackbody, the detector-based temperatures of the NIST Ag- and Au-freezing points are measured to be 1234.956 K (± 0.103 K) (k=2) and 1337.344 K (+0.121 K) (k=2) differing from the ITS-90 assignments by 26 mK and 14 mK, respectively. We find that the temperatures are in agreement with the ITS-90 assigned values within the combined uncertainties.