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Stray radiation and emissivity variation are the most significant causes of measurement error inherent in radiation thermometry. Several methods for reducing errors have been developed by utilizing interreflection of radiation. The first three methods discussed are designed to eliminate stray radiation. The first method, using a water-cooled shielding flange, is applicable for a continuously moving object in a furnace in the range between 200 and 800°C. The second method, having a radiator instead of a cooled shield, is convenient for infurnace measurement higher than 1000°C with accuracy comparable to that of the first method. The third method is designed for the measurement of low-emissivity metals at room temperature where stray radiation is so large that radiation thermometry generally is considered to be impractical. Under the circumstance where the emissivity of the object is not assumed to be constant, the second three methods might be very useful because in these methods the emissivity is simultaneously measured to improve the accuracy of temperature measurement. Specularly reflecting characteristics of the object are utilized in the first and the second methods, while multiple reflection of radiation is used in the last method. Several examples of these methods, routinely used in the steel industry, are introduced. The activities of Japanese societies in the field of radiation thermometry are also surveyed.
radiation thermometry, emissivity, reflectivity, blackbody
Senior researcher, Nippon Steel Corp., Kawasaki,