Research On Algotithm Of24-electode Electrical Capacitance Tomography System Based On High AC Voltage Excitation

Process tomography (PT) technique is a new technique developing rapidly in recent years, which has great developmental potential and wide industrial application prospect in solving the measurement problems of multiphase flow. Electrical capacitance tomography (ECT) technique is a kind of PT technique based on the sensitive principle of capacitance, and it has been the most popular research direction and the main development technique 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.This paper focuses on the research of design of24-electrode ECT system based on high ac voltage excitation and ECT image reconstruction algorithms, which takes applications for large objects as the research background. The main jobs of the paper are as follows:(1) A24-electrode ECT system based on high ac voltage excitation is constructed in laboratory, whose good stability has been tested. Some comparative tests are done by comparing with ECT systems based on low voltage excitation and8-electrode ECT system respectively. The results show that the24-electrode ECT system based on high ac voltage excitation has better recognition ability and qualities of reconstruction images than ECT system based on low voltage excitation and8-electrode ECT system.(2) Image reconstruction simulation experiment based on24-electrode ECT system is carried out in this paper while Landweber iterative algorithm and MLRR iterative algorithm are adopted. Corresponding evaluation indexes are used to evaluate qualities of reconstruction images. Advantages, disadvantages and the best iterative times can be confirmed from analysis and comparison of the results. The results indicate that qualities of reconstruction images and the best iterative times are different for different flow patterns with different duty ratios.(3) Add noises of different levels to simulation data. The experiment results illustrate that qualities of reconstruction images are poorer and poorer with the increase of noise level. The anti-interference ability of MLRR iterative algorithm is poorer than that of Landweber iterative algorithm. That is to say, random noises sensitivity of MLRR iterative algorithm is higher than that of Landweber iterative algorithm. The experiments used MLRR iterative algorithm may be affected by noises more easily.(4) Flow pattern experiments are done on the24-electrode ECT system based on high ac voltage excitation. Several different distributions in sensor are used to test the24-electrode ECT system with the support of LBP, Landweber iterative algorithm and MLRR iterative algorithm. It can be seen from the results that the ECT system has good imaging effect of the common flow patterns, which shows that the increase of electrode number can reduce the difficulty of image reconstruction. Besides, the imaging errors of MLRR iterative algorithm are smaller than those of the other two algorithms for most flow patterns.