Transient Analysis of the AC-based Capacitance Measuring Circuit for Tomography

A Gonzalez-Nakazawa1, J C Gamio2 and W Q Yang1

1 Dept. of Electrical Engineering and Electronics, UMIST, PO Box 88, Manchester M60 1QD, UK, alexnakazawa@hotmail.com

2 Instituto Mexicano del Petroleo, Eje Central L Cardenas Nte #152, Mexico City, D.F., CP07730, Mexico, jgamio@imp.mx

ABSTRACT

The existing AC-based electric capacitance tomography (ECT) system can capture image data at 140 frames/second from a 12-electrode sensor. For some rapidly changing processes, this data acquisition rate is still not fast enough. To optimise the system design, the transient process has been analysed for the capacitance transducer circuit, the AC programmable gain amplifier (PGA) and the phase- sensitive demodulator (PSD). The settling time of each stage is determined and an approach is suggested to minimise them. The results were validated by simulation using PSpice and by experiment, showing that the settling time of the overall ECT system could be reduced from 4.4 ms to 1 ms, indicating a possibility of 1000 frames/second data acquisition rate.

Keywords Capacitance tomography, Circuit analysis, Transient process, Optimisation