Multiwavelength Thermometry at High Temperature: Why It is Advantageous to Work in the Ultraviolet

In principle, multiwavelength radiation thermometry allows one to correctly measure the temperature of surfaces of unknown and varying surface emissivity. Unfortunately, none of the practical realizations proposed in the past proved to be sufficiently reliable because of a strong influence of the errors arising from incorrect modeling of the emissivity and of the limited number of operating wavelengths. The use of array detectors allows a high degree of flexibility both in terms of number and spectral position of the working wavelength bands. In the case of applications at high temperatures, i.e., near 2000 C or above, an analysis of the theoretical measuring principles of multiwavelength thermometry, suggests the opportunity of investigating the possible advantages in extending the operating wavelengths toward the ultraviolet region. To this purpose, a simulation program was developed which allows investigation of the effect of different influencing parameters. This paper presents a brief theoretical introduction and practical analysis of the method. The best choices are derived in terms of the different influencing parameters and data relative to the simulation of both real materials and fictitious emissivity curves and have been studied and analyzed with different emissivity models to check the robustness of the method.