Pyrometric temperature and emissivity determination from statistic of the broadband spectral ratio

Abstract

Non-contact temperature measurements are of high importance when investigating the effect of high energy laser radiation. Classic pyrometric measurements (broadband or one-color) have the limitation that the emissivity of the sample surface must be known, which can vary with wavelength and temperature. Using 2-color (ratio) pyrometers, the calculation can be made without knowledge of the absolute value but only with the ratio of the emissivity at two wavelengths (a value of unity is often used as a rough approximation for closely adjacent wavelengths).This paper introduces an evaluation method that extends the basic idea of two-color ratio pyrometry to a statistical evaluation of a broadband spectrum. A hypothetical temperature is determined from the ratio of the irradiance values for each of the adjacent wavelength pairs. Using these temperatures, a statistical distribution is obtained from which a probable actual temperature of the measuring point results. This temperature on the other hand can then be used to calculate the emissivity as a function of wavelength and temperature. A general problem with unknown emissivity, which cannot be solved even with this present evaluation method, is the ambiguity of a spectrum, as this can result from a large number of emissivity curves, each with an associated temperature.