Size-of-source-effect correction for radiation thermometers calibrated by fixed-point blackbodies

Size-of-source effect (SSE) correction is required when a radiation thermometer measures a radiating source which has a different size from the reference blackbody source that the thermometer has been calibrated with. A simple method for this SSE correction is through the effective source diameter of the fixed-point source. In this paper, the method is demonstrated for a new compact fixed-point blackbody furnace which can be operated for a wide variety of fixed-point types ranging from In to Cu points. A value for the effective source diameter and its uncertainty is derived, which can be applied globally to all fixed-point types and to a wide range of radiation thermometers.