Advance in AC-based capacitance tomography system

W Q Yang

Department of Electrical Engineering and Electronics, UMIST, PO Box 88, Manchester M60 1QD, UK, w.yang@umist.ac.uk

ABSTRACT

An AC-based electrical capacitance tomography (ECT) system has been developed at UMIST, with sinusoidal excitation and phase-sensitive demodulation (PSD). This paper briefly describes the overall system design and then discusses in details the key issues to achieve a high signal-to-noise ratio (SNR) and a high data acquisition rate, including transient process analysis of the first stage, design of an analogue Butterworth low-pass filter and optimisation of the data acquisition process. It has been shown experimentally that the AC-based system has 4 times better SNR than the charge/discharge system, and a data acquisition rate of 140 frames per second has been achieved for a 12-electrode system.

Keywords Capacitance measuring circuit, System design, Data acquisition, Tomography