The Key Technique On Detecting The Concentration Of Sulfur Dioxide With Optical Method

In recent years, the national hazy weather has already clearly revealed the serious ofenvironmental pollution to the people in the world. Sulfur dioxide is not only one of themain air pollutants but also become an important standard to measure the quality of air.Therefore, it is urgently needed to develop an equipment testing gas online so as to controland monitor the SO2effectively. In this thesis, a set of experiment system to detect theconcentration of SO2is designed, which uses the technology of optical fiber sensing,ultraviolet absorption spectroscopy, double optical path different and weak signaldetection.First of all, spectral data model of SO2is established based on the measurementmechanism of ultraviolet absorption spectrometry and fluorescence spectroscopy. Then,through analyzing the absorption characteristic and the fluorescence spectralcharacteristics of SO2, which illustrates the quantitative relationship between theabsorption intensity in ultraviolet absorption wave band and the concentration of SO2.What’s more, it’s easily to deduce the mathematical model, which represents therelationship between concentration of SO2and fluorescence intensity.Secondly, with using the double optical path difference detection technology whichcan reduce the interference caused by the unstable factors of the light source effectively. Aspecial optical path structure is designed to detect the concentration of SO2withabsorption spectrum method and fluorescence spectrum method. In the detectionequipment, the two detection methods share the same light source and detector, realizingthe single system multiplexing technology. What’s more, many circuits are designed thefunctions such as the preamplifier circuit integrated with I/V converter circuit, voltagefollower and differential amplification function, the division circuit and low-pass filtercircuit.Thirdly, the hardware system of data acquisition and control based on FPGA is builtto achieve the following functions: the temperature of deuterium light source and thephotomultiplier tube (PMT) can be controlled in real time; the photoelectric signals isconverted by A/D model and stored by ROM when it outputs the measurement system. the monitoring system is designed through the GUI module in the MATLAB software to showthe data and the observation of data processing which results in real-time dynamically; Atthe same time, the concentration of SO2can be monitored in real-time hours and realizethe serial communication between PCs makes the designed test system more intelligent.Finally, the empirical mode decomposition (EMD) method is applied in the opticaldetection to de-noise the signals, realizing the combination of weak signal detectiontechnology and spectroscopy by comparing the EMD algorithm and wavelet de-noisingmethod. As a result, the effect of the EMD de-noising is prior to wavelet de-noising. Inaddition, multiple experiments are carried out with the processed data signals, and draw aconclusion that verifies the effectiveness of the data processing and the accuracy of thedetection system.