A medium temperature radiation calibration facility using a new design of heatpipe blackbody as a standard source

A blackbody calibration facility which can cover the medium temperature ran ge from 500 to 1200 K has been established. To cover the range from 500 to 800 K, a new design of heatpipe blackbody source which uses a mixture of ca esium, potassium and sodium as the working fluid has been developed. The up per limit of the operating range of this heatpipe is around 1000 K. The tem perature uniformity of the blackbody cavity over two thirds of its length f rom the closed end is better than 0.05% of the operating temperature (in ke lvins). For the range from 800 to 1200 K, another heatpipe blackbody whose working fluid is sodium was manufactured. The temperature uniformity of the blackbody cavity in this device is 0.04% of the operating temperature. The calibration facility consists of a large turntable on which the reference and test blackbodies are positioned and a measurement guide on which an acc urate radiometer is mounted. The measurement procedure yields an uncertaint y of 0.4% (2 sigma) in the calibration of industrial blackbodies.