A complex programmable logic device-based high-precision electrical capacitance tomography system

In this paper, a high-precision measurement system for electrical capacitance tomography (ECT) is presented. A low-cost complex programmable logic device (CPLD) is employed to accomplish logic control, signal generation, data acquisition, digital demodulation and communication with the aid of external components. By adopting a simple digital demodulator recently developed by the authors, the demodulation to ac signals becomes rather simple and resource-saving. A double-T-switches configuration is developed to improve the precision and lower the limit of multi-channel capacitance measurement. A capacitance network is constructed for system calibration. A square ECT sensor with 16 electrodes is constructed to test the practical performance of the measurement system. With a data acquisition rate of 185 frame s^-1, the signal-to-noise ratio and standard deviation of capacitance measurement can reach up to 70 dB and 0.09 fF, respectively. Image reconstruction experiment has validated the CPLD-based ECT system.