The correct selection of the operating wavelength is essential for a precise pyrometric temperature measurement on solar irradiated samples, as the measurement may be disturbed by reflected solar radiation. Atmospheric conditions and particularly the emissivity as basic material property determine the amount of this reflected and the emitted radiation from a sample under investigation. An approach to solve this problem by using a monochromator system for temperature measurement in the UV-B range was developed and experimentally tested. With this system, temperature measurements were possible beginning at 1320°C and ranging up to about 2400°C. Two calculation methods are described and compared. The influence of the calibration temperature on the quality of the temperature measurement is shown. Measurements on a blackbody up to 1500°C were performed for calibration purpose. Temperature measurements on a real solar heated magnesia sample up to 2400°C are presented and discussed. These spectral measurements on hot bodies irradiated in the DLR Solar Furnace led to the final specification of the measurement wavelengths to be in the range from 280 nm to 293 nm.

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