Factors affecting the accuracy of a NIR spectral system for measuring milk constituents

摘要

In this paper, a NIR Spectral System based on Acoustic Optical Tunable Filter (AOTF) was developed for measuring milk constituents. Factors affecting the repeatability of measuring spectra of the system were analyzed by using the transmitted spectra of Ultra-High Temperature (UHT) sterilized milk. Orthogonal experimental design method was employed to determine the significance level of these factors and the optimal condition for measuring spectra of the system. It is concluded that the crucial factor affecting the spectra repeatability is the ambient temperature. Further temperature testing results show that, when the environmental condition is basically invariant, the temperature of the AOTF crystal is basically constant and the drifting amplitude of wave number is within 0.5cm~(-1), when the ambient temperature varies, the temperature of AOTF crystal changes correspondingly. The drifting of wave number is about 1cm~(-1) when the temperature of AOTF crystal changes 1℃. It is found that the wave number drifting increases with decreasing temperature of AOTF crystal. These testing results are of important significance to further improve the measuring accuracy of the system.