Modeling Of A Near-Infrared Detection Circuit And Its Application

NIR (near infrared) spectroscopy analytical technique is one of the most important and widely used technique for content analysis. The Petroleum Properties NIR (PP-NIR) spectrometer based on LEDs and optical filter takes its place among so many NIR spectrometers because of its merits including portable, compact, low cost, low power, high accuracy and so on. However, it also has many defects, such as easily affected by the condition of environment temperature and working voltage, nonlinear characteristics of the detector. This paper uses the modeling method to research the PP-NIR and designs plans to improve the system performance.This paper founds the mathematical model of light sources (LED), and researches its current-voltage and temperature characteristics by simulation; The mathematical model of the detector is founded, and its input and output characteristic and impact factors are researched; The mathematical models including DDS, phase-locked loop(PPL), phase sensitive detector, filter are founded and simulated by Matlab, the results of simulation are given.By the method of modeling, this paper designs serial temperature compensation of the detector. Digital compensation is achieved by programming on the prototype of the PP-NIR. To reduce the voltage noise, a capacitor is designed to connect in parallel on the feedback of the feed-forward amplifier. Based on the research of the feedback linearization, a state feedback controller is designed and proved its validity by simulation.Using the prototype before and after compensation, the experiments including the stability of the PP-NIR and prediction of ethanol content in ethanol-water solution are carried out. According to the analysis of the experimental data, the designs which are used to improve the performance of the PP-NIR in this paper are proved to be practicable.