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Electrical capacitance tomography (ECT) has being widely accepted as a laboratory and industry tool to analyse gas/liquid two-phase flow. For system optimisation and function extension and for getting more information of two-phase flow, a novel extensible ECT system based on field programmable gate array (FPGA) and digital signal processor (DSP) is designed. The new scheme can easily realise not only common single-frequency excitation and demodulation but also new multi-frequency excitation and demodulation. Firstly, a review of classical ECT systems is described, and function extension of our new ECT system is introduced compared to the old ECT system in our laboratory. Then, the design scheme of the new system is proposed in detail. And main parts, such as FPGA, DSP and detection circuit are discussed one by one. Meanwhile, the generation of multi-frequency signals, discrete Fourier transform (DFT) demodulation and digital quadrature demodulation of multi-frequency are described deeply. At last, static and dynamic experiments under condition of multi-frequency excitation and demodulation are carried out to verify the performance of this novel ECT. Experimental results show that this system is of high precision and stability in multi-frequency model. And there is still a future of further extension for this ECT system.
Date of Publication: August 2011