The Design And Research Of Water Quality Measurement System And Algorithm Based On Ultraviolet Absorption Spectrometry

Water is the source of life, it nurtured the Earth’s civilization. The human society can not develop without water. Water quality measurement system provides us a safe and reliable protection. Online real-time water quality detector has been widely used for its real-time, low cost, easy to operate. Currently, water quality detector developed in the direction of automation, intelligent, multi-functional and integrated.In this paper, based on ultraviolet absorption spectroscopy a real-time online water quality measurement system is designed founded by Jilin Province Science and Technology Department Project " Design and study of multi-sensor water environment monitoring system(20140101224JC) ". This paper use FPGA as the control center, give full play to FPGA high processing speed, parallel processing ability. The water quality measurement system can operate without chemical reagents,it is rapid and can display data on-site. It can detect nitrate nitrogen and COD concentration simultaneously which is suitable for real-time detection of clean water and surface water.The following aspects has been studied in this paper:1. Study on UV absorption spectra correction algorithm of measuring nitrate nitrogen concentration. Direct ultraviolet absorption spectroscopy used to detect nitrate and COD concentration in water samples is affected by interfering substances which can result in uncertainty deviation. The ability of eliminate interference by dual-wavelength method, first derivative and second derivative spectroscopy is compared in this paper. The dual-wavelength method is selected to detect the concentration of nitrate in water according to the performance of detector. We measured the absorbance of nitrate at 220 nm and used the absorbance of 275 nm as correction.2. Design of water quality measurement system structure. The water quality measurement system includes 4 sections: light source, spectroscopic system, the sample cell and optical detection system. This paper select the deuterium lamp as light source, holographic concave grating spectral as main components of the system which is controlled by the stepper motor. Photocell converts the optical signal to electrical signal, then the electrical signal pass through the amplifier andanalog-digital conversion circuits. The results are displayed by LCD. The measurement system is small, automatical, rapid and real-time display.3. Complete the control software of the water quality measurement system. This article used FPGA and Verilog on water quality measurement system for programming and controlling, to realize the precise output of selected ultraviolet wavelength and the acquisition of spectral data, to establish algorithm and inversion models.4. The water quality experiment carried out by water measurement system.Based on the completion of the measurement system and the analysis of instrument performance, according to the standard solution experiments and the water sample test application experiments, the reliability of water quality measurement system has been verified.