Design of a 16-electrode ECT System with Combined and Non-combined Electrode Mode

摘要

In a usual electrical capacitance tomography system, each electrode employs its own capacitance measuring circuit and the projection data resulting from the same excitation electrode are converted into DC signals in parallel. In this paper, a common AC-based capacitance measuring circuit with sine-wave excitation and phase-sensitive demodulation is used to eliminate the difference among the measuring circuits in parameters and reduce hardware cost. A CMOS switch network is used to determine each electrode's mode to be excitation, detection or idle. The switch network can support not only an N-electrode (N≤16) ECT sensor operating in non-combined electrode mode, but also a 16-electrode ECT sensor operating in 2-electrode combination mode. Key issues in design are discussed. The system runs well and can monitor the change of dielectric material distribution inside a pipe continuously. Examples of reconstructing images online and history review are given.