Design And Implementation On The Hardware Of Large-Scale Sensor-Based Electrical Capacitance Tomography Systems

Electrical Capacitance Tomography (ECT), which is used for the visualization of multi-phase flows in closed pipes and containers, is widely applied to industrial process monitoring due to its advantages of being non-intrusive, non-invasive, low cost, resistant to high temperatures, simple structure, etc. Currently, however, a majority of industrialized ECT systems are based on small-scale sensors (diameters range from 5 cm to 20 cm) which are compared with large-scale containers, e.g. sugar-refining tanks (diameters are not less than 1 m). Consequently, the existing ECT systems based on small-scale sensors cannot meet the demand for visualizing sugar-refining processes in the tanks. Therefore, it is necessary to design an efficient large-scale sensor-based ECT system.In this paper, on the basis of previous results, a large-scale sensor-based ECT hardware system is designed, fabricated and tested, and the main content and results are as follows:1. Detailed technologic advances about ECT, which mainly include the design and implementation of multiple-scale sensor-based ECT systems, are elaborated and an initial hardware framework of large-scale sensor-based ECT systems is proposed.2. A large-scale sensor-based ECT simulation model based on Finite Element Method and comprehensive performance evaluation functions of ECT sensors are elaborated, sensor structure parameters are optimized and a large-scale ECT sensor is designed and implemented.3. The hardware of the large-scale sensor-based ECT system is designed and implemented, and key modules of the system are analyzed. In order to eliminate strong stray capacitance measuring interference introduced by the large-scale ECT sensor, a method based on cable-driven technology, double-T-switch connection and digital demodulation circuit is proposed. Meanwhile, because of the low sensitivity in the center area of the large-scale ECT sensor, double excitation mode is proposed.4. The maximum length of the cables which can maintain the regular operation of the large-scale sensor-based ECT system and the overall hardware performance are tested. The stability and the anti-stray capacitance interference ability of the system are analyzed. Preliminary imaging studies are conducted by using the data which is measured by the proposed system. Experimental results show that the maximum cable length of the ECT system based on a large-scale sensor(the diameter is 1 m) is 3.9 m, the system can obtain good stability and the anti-stray capacitance interference ability by using the proposed method under double excitation mode, meanwhile, the system has the ability to clearly identify the sucrose test substance.