| Water is the important resource to maintain the survival and development of human beings. However, with the continuous advance of China's industrialization and modernization, a large number of industrial wastewater and domestic sewage caused increasingly serious water environment pollution. Enhancing the control and supervision on the aquatic environment is imminent. Chemical oxygen demand(COD), as one of the most important parameters to measure water quality status, which is indispensable in water environment monitoring. It is of important practical significance to realize the real-time and on-line monitoring of COD parameters of water quality.Indeed, there are numbers of technical principles and methods to detect COD of water quality. The COD detection method based on the UV visible(Ultraviolet-Visible: UV-VIS) spectroscopy has many incomparable advantages. It not only has high sensitivity, good repeatability, high detection accuracy and fast analysis speed, but also can realize the online and in-situ measurement of COD parameters in various scenarios, such as surface water, domestic sewage, industrial wastewater. Especially when it combines with wireless sensor network, we can construct a distributed real-time on-line monitoring system of water COD, which can achieve full coverage of water quality online monitoring basin, also, can meet the urgent needs of the department of industry for joint prevention and control of the water quality.This study is supported by the science and technology project of Sichuan province(number: 2012SZ0111) and Chongqing graduate research and innovation project of scientific research application(number: CYS14039). Following the development trend of miniaturization, intelligence and automation,On the basis of investigation on current situation and developing trend of water quality monitoring technology in domestic and abroad,a distributed water quality COD on line monitoring system based on wireless sensor network and UV visible spectrum has been proposed to realize the real-time and on-line monitoring of COD parameters of water quality.This thesis mainly carried out the following research work:(1)Developed hardware system of water quality monitoring device based on UV-VIS. Based on the function and requirement analysis of monitoring device, following the modular design principle,this terminal uses Ocean Optics pulse xenon light source, USB2000+ industrial grade optical fiber spectrometer and Avantes' immersion spectroscopic probes as the water quality information of spectral acquisition system, combines with the low power consumption and high performance embedded ARM? CortexTM-A7 dual core processor, utilizes dual channel design of two stage amplifier circuit to expand communication distance, thus, developed and designed a water quality monitoring terminal with low power consumption, small size, long transmission and fast response(2) Studied the algorithm of compression and restoration of water quality monitoring spectrum based on compressive sensing. Due to big size and high redundancy of the UV-visible absorption spectrum data of water quality COD, meanwhile, during the transmission many problems may occur, such as packet loss. Using the method of combining wavelet transform with compressive sensing can significantly reduce the amount of data transmission while still preserving spectral characteristics. This algorithm has good robustness, which can still high quality reconstruction of the original spectrum at a certain packet loss rate when below 25%.(3)Realized the establishment and maintenance of wireless sensor network, and designed the data communication protocol and distributed database. In order to manage the equipment in wireless sensor networks, monitoring device uses the networking and heartbeat mechanism. In this way, the wireless network is of good flexibility and expansibility, and can grasp the operation status of the equipment in the network in real time. According to the characteristic of the network data transmission, following the idea of hierarchical design, describes the data link layer, transport layer and network layer design and implementation from the engineering point of view, which enhanced the robustness of the network and ensured the data transmission efficiently and reliably. Designed distributed database to solve the problem of data storage water quality monitoring system, and the lost data also can be restored by it.Finally, tested the performance of the COD monitoring device prototype and water quality monitoring system, it turned out that the water quality monitoring device has a good performance in practical application, and the water quality monitoring system can meet the needs of on-line and real-time monitoring. |
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