Principle and Application of the Pyrometry by Use of Function Fitting Method to Thermal Radiation Spectra.

Abstract

It is not difficult to observe spectra of thermal radiation emitted from a hot surface. It is very interesting to develop the pyrometry to determine the temperature on the basis of thermal radiation spectra. There is not yet sufficient theoretical analysis for the pyrometry, which was termed the spectrum method in this paper. This method also will not be free from the so called emissivity problem. For solving this problem, this method assumed a linear wavenumber-dependence of the emissivity. The theoretical analysis predicted that there was the particular linearity that led to no temperature determination. The present work described the requirements for permissible linearity. The conventional two-color method assuming constant emissivity was applied to the spectrum data and the determination errors due to the deviation from the constant were estimated. A temperature-emissivity diagram was made to show the applicability arrangement of the spectrum and the two-color methods in the spectrum pyrometry. It was found that these methods were able to play complementary roles to determine temperatures. This diagram was useful for predicting the feasibility of temperature measurement. A temperature measurement technique combining both methods was proposed and applied to silicon carbide tube and platinum ribbon heaters. This technique proved to be useful, although it still needs more accumulation of empirical knowledge about how to choose wavenumber range.