The Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST) has performed 10 calibrations of low-background blackbodies since 2001 when the calibration facility and calibration method for low-background blackbody calibrations were significantly improved. Data from 9 of these blackbody calibrations is presented showing a surprisingly large spread in blackbody performance. While some blackbodies performed relatively well, none showed radiance temperature to contact thermometry agreement to within the 1 s calibration uncertainty over the entire operating temperature range of the blackbody. Of the 9 blackbodies reported 5 of the blackbodies showed temperature errors of greater than 1 K, or 3 s. A detailed discussion of calibration uncertainty is presented with examples to support claims of calibration accuracy. Generic blackbody cavity design features are discussed and correlated with blackbody performance. Data will also be presented on the performance of the Absolute Cryogenic Radiometers (ACRs) that are used as detector standards in the calibration of the blackbodies. Recent inter-comparisons of all the LBIR ACRs with a trap detector calibrated against the NIST primary optical power measurement standard will show that ACRs used to calibrate the blackbodies are suitable detector standards and contribute minimal uncertainty to radiance temperature measurements of the blackbody cavities.
absolute cryogenic, ACR, blackbody, calibration cryogenic, LBIR, low-background, NIST