Research On Combined Electrical Capacitance Tomography System

Multiphase flow system is a complex, nonlinear system. There are interface effect and relative velocity between these multiphase flow. That causes the difficult of measurement of multiphase flow. In the world, the multiphase flow is an exploration research field, which is waited to develop urgently. Process Tomography (PT) technique, which has been developed rapidly in recent several dozens years, has great developmental potential and wide industrial application prospect. Electrical Capacitance Tomography (ECT) has many distinct advantages such as low cost, wide application field, simple structure, non-invasive measurement and better safety, ECT has being the most popular research direction and the main development in process tomography technique. There is still a lot of work to be done before practical use of the technique.The object of this dissertation is on the research of 16-electrode Electrical Capacitance Tomography system. So an ECT system of AC measurement combined has studied. Because of their immunity to stray capacitance, two types of capacitance measuring circuits are the most suitable for the use in ECT systems. They are the charge / discharge circuit and AC-based circuit .This paper describes the ECT system with AC-based circuit in detail, and instability is improved by using soft compensation in real time.In the ECT system, the measurement of the low value capacitance is one of the keys and the difficult problems. It requires that the output of the phase shift circuit in the hardware device and the detected signal are synchronous in high precision. But in fact, reach synchronous by calculating phase degree has large limit. But in electrical capacitance tomography system, it has a large amount of distribution capacity, different distribution capacity produced different phase again, so the distribution capacity has very great influence on detection system. It introduces a kind of ECT detection system of without distribution capacity influence in the test, this system uses relevant technology to dispel the influence of distribution capacity, and thus it enhancesECT detection system. The application of phase-locked and synchronous detection reduce the cost of the whole system and improve the sensitivity. Carrier signal and modulation signal achieve entirely synchronous too.A MCU based data acquiring system has been developed, which can communicate with upper computer expediently and fleetly in real time, also advance the speed of data acquisition and processing. At the same time, the corresponding software and hardware design and the debugging has been completed, provides the high quality data for the image reconstruction. It has an innovation point in the paper, PLL (Phase Locking Loop) is used for tracking, it makes ECT system capacitance testing for more precise.