Performance of portable near-infrared spectrometers is easily affected by various factors such as on-site environment, which results in a certain deviation in the on-site predicted results. Partially least square regression (PLSR), as a multiple linear regression method, has been widely used for the analysis of near-infrared (NIR) spectroscopy. However, due to the nonlinear characteristics of the relationship between spectral data and dependent variables, PLSR can easily lead to model errors. Stability and predictability decreased when PLSR is applied in on-site quick detection. How to reduce the errors caused by various environmental factors in the use of portable near-infrared spectrometers is a key issue in promoting the wide application of rapid detection technology based on near-infrared spectral analysis. In this study, the absorption spectra data of glucose solutions of different concentrations are collected by a portable near-infrared spectrometer. Several nonlinear correction algorithms are applied to study the effect of environmental interference during the measurement process. Firstly, the collected spectra data is preprocessed. Secondly, the data is modeled by nonlinear correction algorithms such as optimized artificial neural network (ANN), support vector regression (SVR), and random forest (RF). The impact of different models is compared with to the results using PLSR. It is found that compared with the PLSR linear method, the ANN, SVR and RF nonlinear correction algorithm can eliminate the interference of environmental factors in different degrees. Therefore, ANN, SVR and RF algorithm can improve the prediction accuracy of the model. This study shows that the use of nonlinear correction algorithm for data modeling of portable near-infrared spectrometers can effectively improve the predictive performance of the model.
KEYWORDS: Spectroscopy, Optical attenuators, Near infrared, Near infrared spectroscopy, Control systems, Power supplies, Absorption, Signal attenuation, Lamps, Attenuators
A near-infrared spectroscopy system is developed to measure accurately content of grain nutrient. The spectroscopic system mainly consists of near-infrared spectrometer, halogen lamp, stepping motor module, light attenuator, volume weight module. Since the absorbance of grain in NIR range is relatively high, a new type of light attenuator is developed to precisely measure the reference spectra. The method to obtain the transmission spectra is discussed in this study. The control system running on Windows operation system is also developed to acquire spectral data and process the obtained data. The control procedures are presented in detail. The spectroscopic system can automatically complete the measurement by the control system. The results showed that the present design can obtain the transmission spectra of grain effectivly
The Poloidal and Tangential X-ray imaging Crystal Spectrometers (PXCS and TXCS) were developed on Experimental Advanced Superconducting Tokamak (EAST) to provide spatially and temporally resolved plasmas ion temperature (Ti), electron temperature (Te) and rotation velocity (poloidal- and toroidal-, Vp and Vt) profiles. Each spectrometer consisted of a spherically curved crystal and a CMOS pixelated X-ray Detector. Both spectrometers have recently been upgraded to enhance their measurement capabilities and stabilities. A He-like argon crystal (2d=4.913Å) is deployed on the TXCS and a double-crystal assembly including a He-like argon (2d=4.913Å) crystal and a Ne-like xenon (2d=6.686Å) crystal is deployed on the PXCS. To obtain the optimal spatial resolution, the distance from the crystal to the detector and to the plasma center are modified. Meanwhile, the projection angle of the TXCS sightline to the major radial direction is increased from ~ 22.5º to ~ 29.5ºin order to view the plasma with more tangential component. The XCS server is moved from the EAST tokamak hall to an outside lab to avoid harsh electromagnetic environment and thus enhance stability. Finally, the experimental results from the upgraded XCS systems are presented. New spectral lines of Zinc-like, Copper like and Gallium-like tungsten are identified, which are diffracted by the He-like argon crystal. High-quality He-like argon and Ne-like xenon spectra are observed simultaneously on one detector for measurements of plasmas with wide temperature ranges. Comparison of the Ti- and Vt- profiles measured by TXCS with those measured by charge exchange recombination spectroscopy (CXRS) shows that the results are in well agreement, verifying the reliability of the upgrade of the spectrometers.
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