A High-Speed Digital Electrical Capacitance Tomography System Combining Digital Recursive Demodulation and Parallel Capacitance Measurement

Abstract

Abstract-Two means can be used to improve the data acquisition rate of the ECT system with a fixed excitation frequency, i.e. improving the capacitance measurement speed or changing the capacitance measurement mode from serial to parallel. This paper presents a newly developed high-speed electrical capacitance tomography (ECT) system by combing digital recursive demodulation and parallel-mode capacitance measurement methods. By using the digital recursive demodulator, the time-cost for one time of capacitance measurement can be one period of the excitation sinusoid or less. By using the parallel-mode capacitance measuring unit, capacitances between the exciting electrode and all other measuring electrodes can be measured simultaneously. The data acquisition rate of the parallel-mode ECT system with a sensor of N electrodes is N-1 times of a traditional serial-mode ECT system with the same excitation frequency. When the excitation frequency is 100 kHz and 0.6 periods of data are used for signal demodulation, the data acquisition rate can reach up to 15150 frames per second. The developed system together with a heat-resisting circular ECT sensor with 12 electrodes was used to monitor the ignition process of a cylindrical flame generated by a Bunsen burner. Experimental results show that the ECT system can locate the position and capture the dynamic process of the flame with a high temporal resolution.

Real-Time Imaging and Holdup Measurement of Carbon Dioxide Under CCS Conditions Using Electrical Capacitance Tomography

“…A sine-wave excitation signal is generated by CPLD, DAC, and LPF based on the Direct Digital Synthesize (DDS) technique. The capacitance is measured with the C-V converter using AC-based method [15], [19]. The internet device is used for data communication between the capacitance measurement unit and the host PC.…”

“…Among these tomographic techniques, electrical capacitance tomography (ECT) is an imaging technique to obtain the permittivity distribution in the interior of the pipe from capacitance measurements at external boundary [13]- [15]. ECT is one of the most promising techniques for multi-phase flow measurement, which has been successfully applied to gas-oil two-phase flows in oil industry [16] and gas-liquid-solid three-phase flows [17].…”

“…ECT is one of the most promising techniques for multi-phase flow measurement, which has been successfully applied to gas-oil two-phase flows in oil industry [16] and gas-liquid-solid three-phase flows [17]. It has several advantages such as low cost, high speed and non-invasive compared with other tomographic techniques [15], [18], [19].…”

A Recursive Demodulator for Real-Time Measurement of Multiple Sinusoids

“…Because the response sensor signal is also composed of multiple sinusoids with the same frequencies and the frequencies are pre-known, only the amplitudes and phases of the sinusoids need to be obtained. The active measurement is required in many industrial and biomedical applications, such as industrial process tomography [1]- [3], bio-impedance measurement [4]- [6], eddy current testing [7], [8] and built-in self-test [9], etc. Because the characteristic parameters of the target object are often rapidly changing, real-time and fast measurement of the amplitudes and phases of multiple sinusoids in the response sensor signal is highly desired in sensor data processing.…”

“…To deal with the problem that the quadrature method requires one complete or integer periods of a sinusoid for demodulation, a recursive least squares method [19] and an information-filtering method [1], [20] were ever proposed for the demodulation of a singlefrequency signal by the research group of the authors. Each of the two methods can output a preliminary demodulation 2 result using the first two samples although the accuracy is very low.…”