Evaluation of the radiation characteristics of a high-temperature blackbody

Development of a new spectral irradiance scale realization at the National Institute of Standards and Technology (NIST) requires a careful and complete calibration of a high- temperature blackbody between 1200 K and 2800 K. Filter radiometers have been calibrated to measure the spectral radiance (or radiance temperature) of the blackbody. Using a monochromator, the blackbody spectral radiance will then be used to determine the spectral irradiance distributions of primary and secondary spectral irradiance lamp standards at NIST. In this paper, a calibrated pyrometer and V((lambda) ) filter radiometer will be used to evaluate the high-temperature blackbody for determination of the optimum calibration method for the blackbody. The blackbody apparatus will be described in detail. When the power supply is the sole source of current control, the blackbody current is stable to within 0.056%, resulting in 0.72% for the uncertainty in the blackbody spectral radiance. To achieve our goal of 0.1% in the final blackbody radiance, a blackbody current stability of 0.007% is required. Due to the day-to-day variations in the current, calibrations of the blackbody msut be made frequently. Several feedback control options are recommended as possible solutions for improving both the short term and long term current stability.