Electrical resistance tomography using a bi-directional current pulse technique

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. Potential difference measurements are made on both the positive and negative half cycles and subtracted, cancelling any DC components present at the measuring electrode solution interface. The resulting voltage is a function of conductivity distribution in the medium. This technique is considerably simpler than conventional systems involving the injection of sinusoidal current followed by synchronous 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. The Newton-Raphson (NR) algorithm was used for reconstruction. Experiments were performed on a model system of (a) non-conducting object(s) in a conducting liquid, and on liquid foams of varying bubble size. Visualizations showed that the system could resolve the position and size of the objects, and identify coarse foam regions.