Research On The Capacitance Transducer And The Data Acquisition System In 12-Electrode Electrical Capacitance Tomography

Electrical capacitance tomography (ECT) technique is a kind of PT technique based on the sensitive principle of capacitance, and it has been the main development direction and the most popular research hotspot of PT, due to its many distinct advantages such as no radiation, no invasion, high speed of response, simple structure, low cost, wide application range, better safety and so on. But there is a long distance in practical application and there are some problems and difficulties in system design and application. So there is a lot of work to be done in order to use the technique in the industry as soon as possible. This dissertation goes deep into research of ECT key technique in its hardware designing. Some experiment devices based on 12-electrode ECT system have been designed. The main work and contributions are as follows:It points out the important meaning of multiphase flow measurement to the science research and industry production based on the background of problem studied, analyzes the features and parameters of multiphase flow and sums up the current status and developing trend of the multiphase flow measurement technique. The basic principle, features and problems faced of process tomography are discussed. The principle and constitution of electrical capacitance tomography system are analyzed and mathematical model of sensitivity field is proposed. The current status of ECT technique is discussed. The 12-electrode capacitance transducer is designed based on the influence of structure parameters and design ruler. A switch controlling circuit of transducer electrode array is designed, which can be used to many transducer interfaces. All the electrodes use the same excitation source and C/V converting circuit. Several kinds of familiar capacitance measurement circuit are discussed. A C/V converting circuit based on AC is developed, which has antijamming ability for the stray capacitance, high resolution and low drift. The circuit has good characteristics and is applied in this system. The determination of parameters in the measurement circuit is discussed. The method of circuit design based on front compensation is proposed, and the design of phase sensitivity demodulation and low-pass filter circuit are done. The effect of CMOS switch coupling capacitance to the instability of system imaging is analyzed and compensated by a software approach in real time.