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.
This paper describes a multi-plane implementation of a current-pulse electrical resistance tomography (ERT) data capture system. This is achieved by extending a single plane system, with 16 electrodes and 16 parallel measurement channels, to a one capable of acquiring data in a specified sequence across multiple planes (up to eight) by inserting multiplexer modules in parallel between the instrument and the electrode array. This approach allows high-speed capture systems to be configured for applications such as dual plane cross-correlation velocity measurements or more complex current injection and measurement sequences yielding 3D data sets. The measurement timing and multiplexer measurement sequences are implemented by an embedded processor. Both the executable code and the measurement sequence tables are downloaded to the instrument at start-up. This allows flexibility in specifying the data acquisition sequences and timing required for specific applications without modification of the hardware or embedded code. The effect of measurement noise on the estimated conductivity is quantified and spatial resolution discussed for the case of a 2D online imaging algorithm. Example reconstructions from recorded data sets are presented which verify the operation of the instrument.
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