The Research On Electrical Capacitance Tomography System

Electrical Capacitance Tomography (ECT) is a kind of Process Tomography (PT) based on capacitance sensor. ECT has the advantage of being non-intrusive, fast in response, low in cost and safe. It has become one of important techniques for two-phase flow parameter measurement. But there are some problems and difficulties in ECT designs and ECT applications. This dissertation goes deep into research of ECT key technique in its hardware designing, such as a high-sensitive AC-based capacitance measuring method, the design of array of sensing electrode and data acquiring system. The main contribution and results are as follows:(1) The basic principle and characteristics of PT are compared. The basic principle, system structure and characteristics of ECT are discussed.(2) An AC based C/V converting circuit is developed. The circuit has good characteristics and is applied in ECT system.(3 ) The influence of stray capacitance and its change on the C/V circuit is discussed, and it can be concluded that the influence of stray capacitance and its change is very little comparing to that of the excitation signal.(4) The architecture of array of sensing electrode has been designed which can support up to 16 measurement channels, i.e., it can work with either a single plane sensor with up to 16 electrodes or a twin-plane sensor, a velocity profile may be measured by cross correlation. Because any electrode or electrode combinations can be programmed for either excitation or detection, this system facilitates the investigating of different measurement protocols, such as the use of combined electrodes.(5) The effect of CMOS switch coupling capacitance to the system instability is analyzed and compensated by a software approach in real time.(6) A 16-electrode ECT system experimental equipment is developed. The low and upper computers of the system work in the parallel, which enhances the real-time ability of the system.(7) Experimental equipment is debugged in success, and testing experiments for lower-computer are implemented on the equipment. Experiments show that the experimental equipment is suitable for the application of the real-time detection.