Fast Emissivity Measuring Apparatus With Adjustable Focusing and Field Calibration

A fast emissivity measuring apparatus in the range of 1.4–<inline-formula> <tex-math notation="LaTeX">$2.5 \mu \text{m}$ </tex-math></inline-formula> with adjustable focusing and field calibration has been developed in this article. Benefiting from the portable, fast, and efficient characteristics of the fiber optic spectrometer, the rapid in situ emissivity measurement in industry, such as aluminum profile casting or molten-salt monitoring, can be realized by this apparatus. The light path system of this apparatus is designed based on the principle of the Newtonian reflecting telescope, and the relationship between the radiation signal and the object distance is analyzed in detail. The focus adjustment of the apparatus improves the radiation entering the system, thus ensuring that the measurement signal does not decrease rapidly with the increase in distance. The emissivity of silicon carbide (SIC) and pure silicon is calculated by the Fresnel formula and the results of measured emissivity by the apparatus are in good agreement with the data of theoretical calculation, which verifies the reliability of the apparatus. The maximum error of calibrated radiation of this apparatus is not more than 2.5%, and the average error is less than 1% in the wavelength range of 1.4–<inline-formula> <tex-math notation="LaTeX">$2.5 \mu \text{m}$ </tex-math></inline-formula>. In a feasibility test, the relative combined uncertainty of the spectral emissivity of SIC is less than 5.73%.