Research On Detector Interfaces And Data Analysis Of Near Infrared Spectroscopy Based On FPGA

Near Infrared Spectrometer (NIRS), with the characteristics of small and specialty, intelligent and on-line detecting function, is urgent to apply for agricultural products quality detection. Earlier NIRS of detecting wheat nutrients, CA-NIR-WN03, which was developed by ourselves, has a narrow wavelength coverage. Therefore this paper researched on the technology of acquiring data of NIRS, and developed a new data acquisition system which can detect the wavelength of 0.9-1.7μm. Then we analyzed the effects of different data preprocessing methods on predicting model of wheat protein content. The main research of this paper are as follows:(1) In this paper, the hardware system of data acquisition of the near infrared spectroscopy was modularly designed. With modular method, the hard ware circuit contained five parts, namely FPGA modular, G9214-512S driving modular, A/D7961 data collection modular, RS422 port modular and power modular. By modular design of data acquisition system, modular layout of hardware, it was convenient to debugging. What’s more, it improves the capacity of anti-interference by separately design of analogue function and digital function.(2) The controlling and driving function of FPGA was realized by VHDL language. Modular and step by step design method were adopted, and state machine was used in the realization of each function module and the communication between the various modules, which simplified the problem and improved the efficiency.(3) Experiment was conducted to analyze the performance of data acquisition system. The data acquisition of G9214-512S Video signal was performed under the conditions of absence of light and saturated light. The results showed that the under the absence of light condition, video output of G9214-512S is 0.02V with fluctuation range of 0.14V; however, under the condition of saturation of light, it is 3.2V with fluctuation range of 0.2V. These two experiments has same conditions, that is the cycle of AD-Triger is 8 us and high voltage of it is 3.3V, which are in accord with the G9214-512S datasheet.(4) Preliminary trial of detecting wheat protein with near infrared method was conducted through setting up chemometrics model by cross validation method, and four methods of data preprocessing were analyzed. The result demonstrated that optimal model is acquired through the first-order derivative method and a first order derivative added minus a straight line method.