Determining the integrated cavity emissivity of blackbody furnaces

An apparatus has been constructed for determining the integrated cavity emissivity of blackbody furnace simulators near 500 K and for calibrating infrared detectors. A difference‐ratio method is described for measuring the radiant emission characteristics of the simulator by using a high‐quality heat‐pipe blackbody as a standard radiant source operated at 500 K and a water‐immersed cavity as a reference source operated at a lower temperature. It is verified that the total uncertainties of the method are less than 0.6% for determining the integrated cavity emissivity and 0.5% for determining irradiance from the 500‐K standard blackbody on the detectors.