High-Transmission Filters for Realizing Gray-Body Radiators.

Calibration of infrared radiation thermometers at non-unity emissivity settings is a poorly solved problem for establishment of traceability to meet user needs, for instruments with both fixed and variable emissivity setting functions. A variable-temperature gray-body radiator having a constant value of emissivity independent of both wavelength and temperature can be a perfect tool for the calibration purpose. In this paper, two types of high-transmittance optical neutral density filters, one utilizing a rotating-sector optical chopper, and another of a wire-mesh type, are shown to perform well with a precise transmittance between 90 % and 100 % in the wide infrared wavelength range. These optical filters in combination with a blackbody cavity traceable to ITS-90 can realize reliable gray-body radiation. These methods are applied successfully to several models of infrared thermometers operated in the emissivity correction mode. [ABSTRACT FROM AUTHOR]