Virtual Instrument for Online Electrical Capacitance Tomography

Electrical capacitance tomography (ECT) is a technique invented in the 1980’s to determine material distribution in the interior of an enclosed environment by means of external capacitance measurements (Huang et al., 1989a, 1992b). In a typical ECT system, 8 to 16 electrodes (Yang, 2010) are symmetrically mounted inside or outside a cylindrical container, as illustrated in Figure 1. During the period of a scanning frame, an excitation signal is applied to one of the electrodes and the remaining electrodes are acting as detector electrodes. Subsequently, the voltage potential at each of the detector electrodes is measured, one at a time, by the measurement electronics to determine the inter-electrode capacitance. Changes in these measured capacitance values indicate the variation of material distribution within the container, e.g. air bubbles translating within an oil flow. An image of permittivity distribution directly representing the materials distribution can be retrieved from the capacitance data through a back-projection algorithm (Isaksen, 1996).While image resolution associated with the ECT technique is lower than other tomographic techniques such as CT or optical imaging, it is advantageous in terms of its non-intrusive nature, portability, robustness, and no exposure to radiation hazard.