The article is directed on metrological characteristics increase and extension of the optical thermometry field of use, including two-color compensative thermometry with a priori averaged adjustment. The investigations have been performed for the tungsten. This metal studied in thermometry and metal optics has tabulated quantitative estimations of emissivity which are similar to the most widespread in metallurgy iron-carbon alloys. To increase the reliability and extend the field of use of obtained results, approximated and linearized spectral distributions of tungsten, as well as their mirror representations with decreasing and increasing, convex, linear, and concave distributions of emissivity have been researched. The influence of qualitative and quantitative characteristics of the spectral distributions of emissivity on their nonlinearity coefficient has been studied. The equation of nonlinearity has been obtained. This equation connects the nonlinearity coefficient at the middle wave with the emissivity value at one of the boundary waves through the measured one-color radiation temperatures at 3 operating waves. With a priori knew quantitative estimates of the nonlinearity coefficient at the middle wave and measured onecolor radiation temperatures, the obtained equation can be used for the calculation of emissivity values at the boundary waves. For example, in the linear spectral distributions of emissivity, the nonlinearity coefficient is equal to 0. The number of solutions for linear distributions of emissivity varies from 1 to 2, and for nonlinear – from 1 to 3. The influence of measurement errors of one-color radiation temperatures at operating waves on the errors of emissivity determination by nonlinearity equation is established. The metrological advantages of two-color compensative thermometry using the emissivity values, corrected by the nonlinearity equation, are proved. It was found, that at the nonselective distribution of measurement errors of one-color radiation temperatures, measurement errors of the object temperature for two-color compensative, spectral ratio, and energy thermometry are insignificant for technical measurements. Under conditions of selective distribution of measurement errors of one-color radiation temperatures, these errors respectively are 0.04-0.25 %; 1.66-9.30 %; 0.18-0.34 %. For nonlinear emissivity spectral distributions, real for tungsten and iron-carbon alloys, the methodical component due to the nonlinearity doesn’t exceed 0.48 %, which is also acceptable for technical measurements. The method has been developed for practically acceptable conditions of primary pyrometric information obtaining.
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