Bi-frequency Sine Wave Electrical Conductivity Measure Instrument

The electrical conductivity of solution is an important parameter of water, which is widely applied in electricity, chemical industry, environmental protection, metallurgy, biochemistry, food and water supply industry. As it is low in price with wide measuring range and its structure is simple, electrode EC measurement is widely used in manufacturing process of industry. Thus, electrode EC measurement is studied in this paper.Based on solution conductivity mechanism and the model of solution's effect under electrode, the factor, which effects conductivity precision, is mainly analyzed. After researching on the problems that traditional methods are facing and comparing and analyzing various methods of conductivity measurement, a new kind of EC device is designed, using bi-frequency sine wave with pulse voltage source. In the solution of temperature compensation problem, online look-up table is used for auto-temperature compensation. The core of the system is chip C8051F020. Forward digital and analog circuit is designed in the system. By using DDS(Direct Digital Synthesis) technic, sine wave of high precision is generated under C8051F020's control of DDS chip MAX038. CD4052 is used to complete the function of measuring range conversion. Through the method of true virtual value, AD637 is adopted for AC-DC conversion. In the system, high accuracy A/D CS5260 is selected for data collection, and serial interface RS-484 is applied for communication with PC. In the temperature collection circuit, Pt100 is used for temperature collection and software is devised to complement the error of temperature.Data is calculated and the system is demarcated via Matlab. From the test, relative error of the system, which is demarcated by liquid is less than 1%. In order to be compatible with ADAM4000 made in Taiwan, a series of protocol is established and the system satisfies industrial demand for real-time measurement and processing. This device is simple in structure, wide in measurement range and high in precision and after further improvement, this system can be adopted in industrial processes.