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Liquid system is widely present in Industrial and Scientific Research, as one of the basic physical parameters of the liquid, the conductivity can not only reflects the conductivity of the liquid, and can reflect the concentration of each component in the liquid and other important information, so research liquid conductivity measurement has a very important significance. Capacitively coupled contactless conductivity measurement method (capacitively coupled contactless conductivity detection, C4D) is an important non-contact conductance measurement method, non-contact, the advantages of simple structure, good robustness. However, as a relatively new measurement method, mainly for laboratory analysis the system better use of the environment, and the pipe size is mainly limited to the capillary channel scale. In view of this situation, this paper based on the new technology, seeking the C4D systems can be used in the field of conventional industrial, preliminary study millimeter pipe has a broader range of applications. Firstly, the system sensor geometry measurement performance analysis, and then analyzes the impact shield, finally, using the law of sensor parameters to build a large-diameter (mm pipes) C4D measuring device. The main work is as follows: (1) build a set C4D measuring device, the set of devices by the excitation voltage source, the C4D sensor, signal processing circuit, data acquisition modules and computer composed of five parts, the collection of experimental data can be easily implemented, recorded and displayed. At the same time, the use of simulation software COMSOL Multiphysics finite element simulation program written in Matlab. (2) The length of the electrode changes in impact of C4D system performance. Carried out research and analysis on a variety of millimeter pipeline simulation and experimental results, studies have shown that increasing the length of the electrode is advantageous for improving the performance of detection system. The effective length of the electrode in the effective length of the electrode within the range, the sensitivity of the system and the length of the electrode is a monotonic relationship, the longer the length of the electrode, the higher the sensitivity, the sensitivity of the system is essentially unchanged; outside the range of the effective length of the electrode. (3) The electrode spacing changes in impact of C4D system performance. Research and analysis on a variety of millimeter pipeline simulation and experimental results, the studies have shown that the electrode spacing becomes smaller, the system output current value larger increase in sensitivity, but the sensitivity curve steepens, and concentration larger than the Fast tends to zero, narrowing the measurement range of the system. (4) Research shield C4D system performance. Confirmed by theoretical analysis and experimental verification mm duct, by the introduction of the ground the shield can effectively eliminate the effects of stray capacitance of the excitation electrode and the detection electrode is formed through the air coupling is advantageous for the detection system in the system, C4D . (5) obtained according to the above rules, select the sensor parameters, the design and development of the sensor and the test of the experimental results. Sensor developed by the tests show that the development of large-caliber performance of the sensor basically reached the level of the existing literature, is successful.
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