Phase Sensitive Demodulation Front-End for Electrical Capacitance Tomography Applications

H. Wegleiter, A. Fuchs, D. Watzenig, H. Zangl, and G. Steiner

Institute of Electrical Measurement and Measurement Signal Processing, Graz University of Technology, Kopernikusgasse 24/IV, A-8010 Graz, Austria, Email: wegleiter@tugraz.at

ABSTRACT

Electrical Capacitance Tomography is a common technique to visualize the permittivity distribution inside closed pipes by means of evaluating coupling capacitances of a multi-electrode assembly. This paper presents a novel hardware concept, capable of measuring the impedance between the electrodes. In order to separate the measured signal into a real-part and an imaginary-part an In- Phase Quadrature demodulator is used. The real-part of the signal represents the conductance G and the imaginary-part the susceptance B of the material inside the pipe. Based on a high frequency low-Z measurement principle a novel front-end circuit is developed and analyzed with regard to its performance (e.g. linearity) and inherent limitations.

Keywords In-Phase Quadrature demodulation (I/Q), Electrical Capacitance Tomography, Carrier Frequency