Research On Projection Data Acquisition System For Electrical Capacitance Tomography

Two-phase flow parameter measurement is a difficulty in field of industrial process parameter measurement. Process tomography (PT)technique can provide interior behavior 2/3 dimension visualizinginformation in process equipment such as closed pipe, vessels andso on in real time, so it is a novel approach for two-phase flow parameters measurement. Electrical capacitance tomography (ECT) is a technique based on capacitance sensor. ECT has the advantage of being non-radiate, non-intrusive, fast in response, simple instructure and low in cost, so it is one technique which has greatdeveloping potential in industrial application. This dissertation goesdeep into research of ECT key technique in its hardware designing, such as the design of array of sensing electrode, a high-sensitive AC-based capacitance measuring method, data acquiring system. The main contribution and results are as follows: 1) The basic principle, characteristics and industrial application prospect of ECT are analyzed. 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 on the C/V circuit isdiscussed, according to its conclusion , the appropriate component , parameter and phase shift is find out .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 facilitatesthe investigating of different measurement protocols, such as the use of combined electrodes.5) The system's sensitivity and SNR can be improved by the method of balancing the standing capacitance using DC offset compensation.6) The system instability is improved greatly by using soft compensation in real time.7) A micro-controller based data acquiring system has been developed, which can provide data for image reconstruction, and the main software has been written.8) To test the performance of ECT system,the 8-electrodes sensor was used.Some test results and evaluation are given.