Modeling and Implementation of AC Electrical Capacitance Tomography

Two means can be used to improve the data acquisition rate of the electrical capacitance tomography (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 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 15 150 frames/s. 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.

An electrical capacitance tomography (ECT) sensor consists of a number of electrodes, which are usually mounted around the external or internal periphery of a circular insulated pipe. Therefore, the diameter of a conventional ECT sensor is fixed. This paper presents a new structure of ECT sensor, which can achieve adjustable inner diameter of the sensor within a certain range, by re-engineering the traditional structure, and therefore the electrode-to-gap ratio (EGR) of the sensor is changed. The relationship between EGR and image quality was studied by simulation. A prototype ECT sensor with variable diameter was fabricated and evaluated with an impedance-analyzer based ECT system. The experimental results show that the ECT sensor with variable diameter can provide similar reconstructed images to a conventional ECT sensor, when the sensor diameter varies in a certain range, i.e. EGR above 6:1. Therefore, this new structure can enable the ECT sensor to be adapted to the change in diameter of the measured objects.

Process tomography technique provides a novel method to investigate the multi-phase flow distribution inside pipe or vessel. Electrical resistance tomography (ERT) and electrical capacitance tomography (ECT) are extensively studied in recent years. As the capacitance to voltage and resistance to voltage converters run faster, the speeds of other circuits in the system, such as MCU, A/D, D/A etc, have become the bottlenecks of improving the speed. This paper describes a new dual-modal, ECT and ERT, data acquisition system. The system is controlled by a digital signal processor. Both the ERT and the ECT systems use one platform to simplify the system design and maintenance. The system can work at high speed which is only limited by the capacitance to voltage converter or resistance to voltage converter. Primary test results show the speed of the new system is 1400 frames/second for 16-electrode ERT and 2200 frames/second for 12-electrode ECT.

Electrical capacitance tomography (ECT) technique has been developed due to its inherent simplicity and low cost. The tomographic images are obtained based on the permittivity differences between the investigated materials and background material (air, in most cases). The dynamic range of capacitance measurements in ECT could be 40 dB or higher. Simultaneously, the changes in the measured capacitances take up only 5% of the full measurement range. Therefore, the capacitance measuring circuit should be of high dynamic range as well as high precision, which constitutes one of the greatest challenges in ECT system design. The standing capacitances in ECT measurements may be canceled by differential measurement. In this paper, a recently developed differential ECT scheme has been presented. An active screen is employed as the differential electrode in the sensor, which is placed between the measuring electrode array and outer screen. Accordingly, a transmitter channel is implemented to accommodate the active screen, which enables the active screen to deliver multi-level AC signal. Simulation and experimental results show that the differential ECT system has a signal-to-noise ratio of 16 dB higher than the previous design, i.e. the non-differential system.

The sensitivity-field distribution of sensors in the electrical capacitance tomography (ECT) system is influenced by the distribution of multiphase-flow media, and the soft-field characteristics can bring great difficulty into image reconstruction. The subject investigated of this paper is major in the ECT system of 8-electrode oil-water two-phase flow. According to the method of finite element simulation, we can analyze the influence of radial electrodes and their embedded sizes on capacitance values and the distribution of sensitivity field in the system, and the embedded sizes of radial electrodes can be determined based on the simulation analysis. Then the dynamic variation range of measured capacitance values and the difficulty in designing the data acquisition circuit can be reduced, the sensitivity of capacitance response is increased, and the sensitivity-field distribution of sensors and the performance of the ECT system are also improved

Based on the 12-electrode electrical capacitance tomography (ECT) system and the ant system algorithm (ASA), a new method was proposed for online voidage measurement of oil-gas two-phase flow. In practical voidage measurement, based on the 66 measurement capacitances obtained from the ECT system, the real-time flow pattern of oil-gas two-phase flow was first identified. Then, according to the flow pattern identification result, an appropriate measurement model was selected, and the measurement voidage value was calculated. The measurement models related to the flow pattern were developed in advance using the ASA. Static and dynamic experimental results show that the proposed voidage measurement method is effective. Moreover, the real-time performance and measurement accuracy are satisfactory.

Electrical capacitance tomography (ECT) has been developed successfully for industrial applications. While most ECT sensors employ a circular structure with a closed sensing area, some other structures like square and parallel are needed for some particular applications. This paper describes a parallel structure ECT sensor, which can provide incomplete measurement data only. The performance of this parallel ECT sensor is discussed based on simulation study with 2D FEM models. Images of different permittivity distributions are generated by linear back-projection (LBP) and Landweber iteration algorithms. The effect of the effective sensing area and distance of parallel plates are also discussed. Both capacitance residual and correlation coefficient are used to evaluate the image quality. The results show that (1) the width of the sensing area should be the same as the shielding layer in order to acquire high quality image and (2) the distance between two parallel plates is suggested being equal to the shielding layer to compromise the sensing space and the sensitivity of the central region.

Multiphase flow metering is a challenging task because of the complexity of multiphase flow. In this paper, nonintrusive multiphase flow metering techniques, including machine learning (ML) / artificial intelligence models for the identification of flow regimes and estimation of flow parameters of a two-phase flow in a horizontal pipe are proposed that use data from Electrical Capacitance Tomography (ECT) and conventional measurements such as differential pressure in the pipe. The flow regimes are classified into five types, namely plug, slug, annular, wavy and stratified. Two-phase air/water flow experimental data from ECT are collected by running extensive experiments using the horizontal section of the multiphase flow rig at the University of South-Eastern Norway (USN). Exploratory data analysis (EDA) is performed on these data to extract features for use in classification and regression algorithms. Time series of normalized capacitance data from ECT sensors are used to classify flow regimes and identify flow parameters. ML techniques of Artificial Neural Network, Support Vector Machine (SVM), K-Nearest Neighbors (KNN) and Decision Tree (DT) are used to classify flow regimes by using features extracted from ECT data. The cross-correlation technique is used to estimate flow velocity using data from a twinplane ECT module. ML regression techniques are used to estimate phase fractions. Fusing data from differential pressure sensors enhances the flow regime classification. An overall system performance is given with suggestions for designing dedicated control algorithms for actuators used in multiphase flow control.

Tomography is a way to describe something non-destructively. Some types of Tomography are Electrical Resistance Tomography (ERT), Electrical Impedance Tomography (EIT), and Electrical Capacitance Tomography (ECT). This study aims to combine the ECT and ERT systems. The combination uses the ERT technique (Borehole method) and develops until it can be used like ECT. This research conducts three significant stages (design making, designed realization, and examination). The examination is carried out by simulation and experimental measurement. The simulation result is compared to the result of the experimental measurement. The result shows that both have the same patterns, but it has the amplitude of voltage difference pattern. It is because the resistivity result affects the measured voltage difference result. The higher the resistivity result of the medium, the smaller the measured voltage difference.Tomography is a way to describe something non-destructively. Some types of Tomography are Electrical Resistance Tomography (ERT), Electrical Impedance Tomography (EIT), and Electrical Capacitance Tomography (ECT). This study aims to combine the ECT and ERT systems. The combination uses the ERT technique (Borehole method) and develops until it can be used like ECT. This research conducts three significant stages (design making, designed realization, and examination). The examination is carried out by simulation and experimental measurement. The simulation result is compared to the result of the experimental measurement. The result shows that both have the same patterns, but it has the amplitude of voltage difference pattern. It is because the resistivity result affects the measured voltage difference result. The higher the resistivity result of the medium, the smaller the measured voltage difference.

Electrical Capacitance Tomography (ECT) is a method to determine the material distribution within the interior of a closed object by measuring the capacitance values across externally mounted electrodes. Traditionally, an AC excitation pulse is applied to a pair of electrodes that form a capacitor during each measurement step, in order to determine the capacitance from the output current measured. This paper investigates how the speed of inter-electrode capacitance measurement can be improved by comparatively studying three methods that affect the way electrodes are excited and signals are received: 1) multiple-excitation-single-receiving, 2) single-excitation-multiple-receiving, and 3) multiple-excitation-multiple-receiving. A PSPICE circuit model was built to simulate the bandwidth and interference between the simultaneously sampled measurement channels. Simulations using ECT sensors with 8 and 12-electrodes have shown that measurement speed can be increased by up to 3 ∼ 30 times as compared to the traditional mode of capacitance measurement. Such new capability opens up new possibilities for ECT as an effective tool for online, real-time monitoring of a wide range of dynamical processes in the industry.

Electrical capacitance tomography (ECT) is a non destructive technique for obtaining the distribution of some physical quantity in a closed pipe by measuring the permittivity distribution. Several conducting plates are fixed around the circumference of the pipe so they do not disturb the flow or movement of materials. The imaging quality of an electrical capacitance tomography system depends upon many co-influential parameters such as number of electrodes, length and width of electrodes, axial guard electrodes, radial guard electrodes, and screen guard. Optimum selection of these variables coupled with advancements in sensing electronics and imaging algorithm provides the best inside view of a closed vessel/pipe. This, in turn, provides better process information for control. This article is intended to summarize such design rules for ECT electrodes and sensors. Numerical simulations were performed using commercially available finite element method (FEM) software to help verify the optimality of the design parameters chosen. Experimental verification was conducted using a fabricated capacitance sensing circuit that could measure capacitance in the range of 1 fF to 7999 femtofarads with a root means square noise level of 0.07 fF. Some parameters such as the thickness of the pipe are chosen as demanded by the process. This article will be useful for researchers to design the ECT Sensors with ease.

This article presents investigation of 3-D electrical capacitance tomography (ECT) sensors with different excitation strategies, including dual-electrode excitation in the same plane, in adjacent plane, in planes separated by one plane or two planes, and in the adjacent position or opposite position in the same or different planes. The results show that a 3-D ECT sensor with dual-electrode excitation in the opposite position provides higher mean capacitance and lower standard deviation than in the adjacent position. Dual-electrode excitation in different planes can increase the capacitance signal and decrease the dynamic range of capacitance measurements, and thus, decrease random errors and improve the quality of 3-D reconstructed images. A 3-D ECT sensor with dual-electrode excitation in planes separated by one plane and opposite position can provide small measurement uncertainty and high image quality.

Study of granular flow in silo based on electrical capacitance tomography and optical imaging

Electrical capacitance tomography (ECT) is a non-invasive measurement technique widely used for two-phase flow imaging and parameter measurement. Image reconstruction of ECT analyzes the capacitance measurements from the ECT sensor and reconstructs the permittivity distribution in the sensing domain through certain algorithms. Due to its ill-posedness, image reconstruction has always been a hotspot and a challenge in ECT research. Over the past decade, the blooming of deep learning has introduced promising avenues for addressing this challenge. Numerous deep learning-based models and algorithms have been developed for ECT image reconstruction, and remarkable achievements have been made. This paper comprehensively summarizes the state-of-the-art deep learning approaches for ECT image reconstruction. In addition, the challenges and future directions of deep learning-based ECT image reconstruction are also discussed in perspective.

Electrical capacitance tomography (ECT) system is useful to obtain information on spatial distribution of dielectric material mixture inside a vessel. This paper discusses a sixteen-electrode mobile ECT sensing system which is developed non-invasively and non-intrusively. Emphases on the software development aspects are presented in several sections; initialization part, normalization part, calibration part, hardware communication part and the image reconstruction part. Thus, the liquid-gas concentration profile of the ECT system is successfully acquired using the software developed.