Uncertainties in blackbody corrections for low-temperature radiation thermometers

Equations are derived for propagating the uncertainties contributing to the blackbody corrections for the calibration of low-temperature radiation thermometers operating over a spectral range near the 8 mu m-14 mu m band. These equations include the full Planck treatment of spectral radiance, which is necessary at these long wavelengths, and account for the thermometer bandwidth. The influence quantities include the source emissivity, reference temperature, reflected ambient radiation, detector temperature, and spectral responsivity. Various cases are considered when using either a blackbody cavity or a flat-plate calibrator as the calibration source, and when using a contact thermometer or a radiation thermometer as the reference. Total uncertainties tend to be smallest when a radiation thermometer is used as the reference as, in this case, the influence of the source emissivity is minimised.