Best Value Design of Electrical Tomography Systems

D Georgakopoulos1, W Q Yang2 and R C Waterfall2

1 National Physical Laboratory, Centre for Electromagnetic and Time Metrology, Queens Road, Teddington, Middlesex TW11 0LW, UK, dimitrios.georgakopoulos@npl.co.uk

2 Dept. of Electrical Engineering and Electronics, UMIST, PO Box 88, Manchester M60 1QD, UK rwaterfall@iee.org

ABSTRACT

All electrical tomography systems are built from similar blocks of electronics: sensor, front-end circuit, gain unit, signal conditioning circuit, switching and multiplexing and analogue-to-digital conversion. How to put the different blocks together depends on the functions needed for specific applications. This paper will concentrate on measuring complex impedance, i.e. both permittivity and conductivity. Three approaches will be considered: (1) measuring two amplitude at the same frequency but different phase, (2) measuring one amplitude and one phase and (3) measuring two amplitude at two different frequencies. Where multiple frequency excitation is required the following methods of implementation will be discussed: sequential frequency sweeping, time series, delta function and sin (x)/x. Finally, six different system designs will be compared in terms of complexity and achievable data acquisition rate.

Keywords Impedance measurement, System design, Spectroscopy, Tomography