Can a thermometer with .01°C accuracy be used to calibrate a blackbody to its full spec of .025°C?
Normally, you want a 4:1 ratio between the accuracy of the calibration equipment and the accuracy of the equipment being calibrated. But acceptable calibration can be achieved even if this guideline cannot be met. The 4:1 ratio comes from MIL-STD-45662A, paragraph 5.2, which specifies that the uncertainty of measurement standards should not exceed 25% of the acceptable tolerance for a characteristic being calibrated. However, MIL-STD-45662A allows deviation from this ratio provided the adequacy of the calibration is not degraded. SBIR’s differential blackbody sources are specified with a total system uncertainty of .025°C for temperatures near 25°C and near zero DT. Calibration is performed using a thermometer with accuracy of .01°C, so a 2.5:1 ratio exists between the measurement standard and the characteristic being calibrated. The limiting factor in calibration of differential blackbodies is the unavailability of a better thermometer. An SPRT and resistance bridge, such as the Rosem
