Abstract
Effect of Stray Light on Spectral Emissivity Measurements
In order to determine the true temperature from the measured color temperature, it is-required to determine the wavelength dependency of the spectral emissivity of a given object. Measurement applying an apparatus with a monochromator and a photomultiplier combined brings about the value of the spectral radiance multiplied by the apparatus factor, the coefficient and constant of measurement, and by others. Then, the relative spectral radiance is determined by dividing the spectral radiance measured in the various wavelengths by that in a certain wavelength λ0, so that the relative spectral property co-efficient of the apparatus is determined, and the coefficient and constant of measurement are eliminated.
Next, as it was found out that the stray light in a monochromator has great effects on the measured value, the stray light degree is defined, the method of determining it is proposed, and the stray light effects on the spectral emissivity measurement are examined.
Consequently, it is obvious that a monochromator with the stray light degree 10-7 and below is to be applied and that a double-monochromator complies with this requirement. Thus, the method mentioned above is checked up to be appropriate by measuring spectral emissivity in visible region in the case of pure iron at 1200°C, using a double-monochromator with the stray light degree 10-8. And in this case, the spectral emissivity is in an approximately linear relationship with the wavelength.
