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The contry’s twelfth five year plan will make efforts on environment protection and enegy conservation and emission, especially strength the monitoring on the key rivers. One of the most important work of environment protection is the control of the sewage discharge and the detection of the situation of the water pollution, COD is of the index to measure the water pollution degree. Now,most of the surface water is polluted, this has threated human health, so monitoring the suface water become an important work.In this paper, the FIA is mainly used for the detection of COD in surface water, and the sensor is designed by environment institute, the sensor’s principle is electro-chemical detection. The system include the design of hardware and software. The part of hardware include the overall framework design, potentiostat potential control circuit and current measurement circuit, analog filter circuit, D/A and A/D change circuit. The system uses distributed power supply system, include switch power supply and analog power supply, analog power is mainly responsible for sensor signal acquisition,switching power is responsible for industrial computer,reversing valves and injection pump. The part of software include PC software and lower level computer software, the language for the PC software is C#, and it’s developed in the platformof VS2008 and runs on the Wince OS. The software used modular design thought,include configuration file module,serial communication module,data processing and graphical display module. The lower level computer software developed on the Keil platform, it include D/A and A/D drive and serial interrupt module, the software mainly collect sensor signal,package the data into the frame,and communicate with the PC.After complete the device, we take test for the voltage control precision, voltage control range and the resolution of the current measurement. The test proved that the device has voltage control precision of 0.1 mv, its voltage control range is-10v～+10v, its current measurement resolution can get to 1nA. The instrument achieve the design requirements.
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