Electrical capacitance tomography (ECT) is an imaging technique for industrial applications. ECT is based on measuring capacitance from a multi-electrode capacitance sensor and reconstructing cross-sectional images, aiming to visualise the distribution of dielectric materials, such as gas/oil flows in an oil pipeline and gas/solids distribution in a fluidised bed. The internal information is valuable for understanding complicated phenomena, verifying computational fluid dynamic (CFD) models, measurement, and control of industrial processes, which are difficult with conventional process instruments. Compared with other tomography modalities, ECT is the most mature and offers advantages of no radiation, rapid response, non-intrusive and non-invasive, withstanding high temperature and high pressure and low-cost.
Research into ECT involves sensor and electronic circuit design, data acquisition, computer interface, mathematics, finite element analysis, software programming, and general knowledge in process engineering. Because of extremely small capacitance to be measured (down to 0.0001 pF) and the nature of soft-field, ECT presents challenges in engineering and mathematics. The University of Manchester (formerly UMIST) pioneered research into ECT. The latest ACECT system presents the state-of-the-art technology, which can generate on-line images at 100 frames per second with 73 dB signal-to-noise ratio (SNR) and has been used for many challenging industrial applications, such as gas-oil-water flows in oil pipelines, wet gas separators, pneumatic conveyors, cyclone separators and fluidised bed dryers. It is foreseen that ECT will make major contributions to the gas/oil, pharmaceutical, power, and other industries. In this Lecture, the principle of ECT, capacitance measuring circuits, image reconstruction algorithms, and some applications will be discussed, together with a demonstration of an ACECT system.
