Current Pulse Technique for Electrical Resistance Tomography Measurements

EW Randall1, AJ Wilkinson1, JJ Cilliers2, W. Xie2 and S.J. Neethling2

1 Department of Chemical Engineering, University of Cape Town, Private Bag, Rondebosch, 7701, South Africa, ewr@chemeng.uct.ac.za

2 UMIST, Chemical Engineering, Manchester, M60 1QD

ABSTRACT

A novel Electrical Resistance Tomography (ERT) measurement system has been developed, which uses a switched bi-directional constant current source to produce the electric field in the measuring vessel. Differential voltage measurements are made between the positive and negative current half cycles. This technique is considerably simpler than conventional systems involving the injection of sinusoidal current followed by asynchronous or DSP based detection. Further, because the current pulse is “DC”, the differential measurements do not require demodulating and therefore the technique has the potential for high-speed operation. The current pulse technique is justified in terms of the electrochemistry occurring at the electrodes and electronic circuitry used.

Experiments were performed on a model system of a non-conducting object(s) in a conducting liquid. The performance of two reconstruction algorithms, linear back projection (LBP) and Newton-Raphson (NR), were compared. In the system where the conductivities are widely different, LBP can detect the position, but not the size of the object(s), while NR clearly delineates them.

Keywords Tomography, ERT, direct current