Design Of Water Conductivity Instrument Based On Dual Frequency Method

Conductivity is a very important parameter of water. Conductivity instrument is used widely in electricity, chemical industry, food, environmental protection, Metallurgy, pharmacy, biochemistry and water industry. With the development of economy and technology, people care more and more about the water quality. For a very long period, how to measure water conductivity precisely is always a difficult problem and aroses more and more researchers and conductivity instrument manufacturers'attention.After referring many references at home and abroad, this paper analyzes the electrode conductivity measurement's influencing factors, mainly three aspects, polarization effect, capacitance effect and the temperature effect, according to the mechanism and solution conductivity electrode solution in the role model. In this paper, a networking and high precision water conductivity instrument based on dual frequency method is developd. The instrument adopts two sine signals with different frequencies as its exciting source, solves the theoretical error on measuring water conductivity and eliminates the error generated by capacitance effect in alternative current method to measure water conductivity. The application of Micocontroller LM3S8962 as the control unit combined with DDFS, RMS-to-DC conveter AD637 and A/D converter ICL7135 makes the instrument possess the advantages of steady performance, high resolution and low distortion. Further, it has the option of TCP/IP, CAN and RS-485 communication interfaces to meet a demand of establishing intelligent measuring and controlling system expediently and freely.The instrument can automatically adjust measuring range and achieves temperature compensation, exceeding conductance limit alarm, network communication, numerical control current source, relay control and so on. The instrument has also the characteristics such as man-machine interfaces, data storage and password setting. PC communicates with Microcontroller with TCP/IP to realize remote acquisition of water conductance, data handling and result display. Users can access the instrument easily by common Web browser. Experiments in different water indicate that the precision is within requirements. This instrument can be used in industrial process after further improvement.