Hardware design of electrical capacitance tomography systems

Electrical capacitance tomography (ECT) was one of the techniques which were firstly developed for process tomography (PT). Two types of capacitance measuring circuits are the most suitable for the use in ECT systems - the charge/discharge circuit and the AC-based circuit - because of their immunity to stray capacitance. Since the standing capacitances involved are relatively large and the capacitance changes to be measured are very small, the standing values need to be cancelled by DC offset compensation or AC feedback compensation. Alternatively, the capacitances can be measured by high-accuracy self-balancing circuits without standing value compensation. In this paper different designs of sensing electronics for ECT systems are presented and the advantages and disadvantages compared.