NEW METHOD FOR MEASURING THE SIZE-OF-SOURCE EFFECT IN STANDARD RADIATION THERMOMETRY

摘要

For temperature measurement by a pyrometer, utilising the heat radiation of the measured object, the component of the measurement uncertainty depending mainly on the source size and called "size-of-source effect" (SSE), is one of the most insidious and difficultly determined properties of the radiation thermometer. This effect is caused by additional radiation reaching the detector of the radiation thermometer not by the usual way in accordance with geometric optics, but by scattering of radiation on defects of the lenses or mirrors, incident from peripheral zones of the object, by diffraction on apertures and interference of reflections on surfaces of the optical elements. For the ideal optics such radiation deviates from the sensing surface of the photodetector or, generally, is cut off by the field diaphragm in a plane of an intermediate image of the measured object. To solve the problem of the determination of the SSE in the real conditions of measurement standard work, the method of measurement with a specially designed device was developed and tested: the blackbody is replaced by a cooled simulator of a target viewed by the radiation thermometer,. The essence of the method is, that in the furnace, heated up to the reference temperature, measurements of the brightness of the cooled simulator target are carried out. In this case, if the cooling of the target simulator is sufficient, its radiation will only be caused by reflection of radiation from the heated cartridge ahead. This radiation can be calculated for known sizes and reflectance of the simulator sheet surface. The parasitic radiation causing SSE reaches the radiation thermometer precisely in the same way as with the blackbody in a crucible at reference temperature, and it can be observed.