Papers by Keyword: Electrical Capacitance Tomography (ECT)

Abstract: Accurate measurement of the concentration of pulverized-coal in various pipes as a guidance to proper control plays a key role in assuring safe and economic operation of a pulverized coal-fired boiler during the combustion process. Experimental studies are carried out on the measurement of a lean mass flow in a pneumatic conveying pipeline using electrical capacitance tomography (ECT). A cyclone separator is employed in this system where the sensors are placed in order to compensate the inhomogeneity of the sensor sensitivity. The distribution of void fraction in radial direction, the average void fraction and the wavy characteristics are analyzed. The feasibility and reliability of the method are verified by the experimental results.

Abstract: The electrical capacitance tomography (ECT) was used to detect multiphase flows in pipelines, fluidization process and combustion phenomena in internal combustion engines, and so on. In the mentioned applications, none of them has equipment or vessel with inner diameter exceeding 1 meter. Nevertheless, there are some of large equipments like blast furnaces, coal bunkers and so on, need to detect its content distribution. These requirements could be met by ECT technology. But there are not any ECT systems can be used to detect content distribution of those large equipments, because the existing system can not measure the capacitance in change which was changed by content distribution. A new method of high AC voltage excitation and C/V circuits which has a higher excitation voltage about 20~50 times than the previous ac-based system, with an 8-electrodes sensor array that is amounted on a 2.5m inner diameter object constructed a High Voltage Electrical Capacitance Tomography (HVECT) system in laboratory. Image reconstruction experiments show that the HVECT is applicable to monitor the content distribution in the future.

Abstract: Sensor sensitivity field in Electrical Capacitance Tomography is affected by the distribution of multiphase medium, which is the peculiarity of soft field, which brings great difficulty for image reconstruction, to improve the quality of image reconstruction, it is important to analyze the distribution of sensitivity field. In this paper, using finite element model, comparing the two different plotting patterns to field, then, expound a new kind of plotting pattern to field, and computer simulation to the distribution of sensitivity field. From experiments, simulation result will be fine if adopting unequal interval plotting patterns, at the same time, the result has high precision.

Abstract: In order to be able to real-time control over the related equipments of pneumatic transportation system and to prevent plugging from happening, here a method that uses an electrical capacitance tomography system and grey correlation analysis to identify two-phase flow patterns is proposed. Firstly, the concrete steps of two-phase flow patterns identification based on this method are expounded in detail. Then the simulation experiment has been finished to prove the validity of this method. The simulation experiment results have shown that this method has higher recognition precision and faster operation speed in the two-phase flow pattern identification. This method also provides an effective means for the two-phase flow pattern on-line identification.

Abstract: This paper introduced an optimum design method of sensor array suitable for electrical capacitance tomography (ECT) based on high AC excitation voltage. The sensor parameters of electrode span and length were optimized in turn, and a sensor model for testing was fabricated according to optimal objects. The image reconstruction experimental resultants of grain distribution indicated that high quality images could be reconstructed by the sensor model. This proved the optimal design method of ECT sensor given in this paper was feasible and the parameters were also credible.

Abstract: An ECT data acquisition system usually has N-1 measurement channels or single measurement channel. In order to solve the contradiction between system speed and system cost, a 16-electrode electrical capacitance tomography system with double measurement channels has been designed. It has good anti-noise ability and stray-immunity by using ac-based capacitance measuring circuits. A switch network is used to set each electrode at excitation mode, detection mode or idle mode. The influence of switch coupling capacitances is discussed and its soft compensation method is proposed. By using LabVIEW, remote monitoring and distributing data or images over network can be implemented easily.

Abstract: Two kinds of sensor structures for 3D direct capacitance imaging are presented. 12 electrodes are arranged in three planes each with four electrodes. Every four electrodes on each plane are rotated 45° (sensor 1) or 0° (sensor 2) with reference to the previous. A comparative study between the two sensors shows that although the difference in sensor’s sensitivities and outputs is obvious, the difference in reconstruction images isn’t apparent, at least for some permittivity distribution. The output range of sensor 1 is smaller than that of sensor 2, thus sensor 1 is better than sensor 2 in terms of the design of a capacitance measuring circuit. Both sensors can achieve 3D direct capacitance imaging with a good axial resolution.

Abstract: To solve the‘soft-field’nature and the ill-posed problem in electrical capacitance tomography (ECT)technology, a novel preconditioned conjugate gradient algorithm for electrical capacitance tomography is presented. The analysis of the basic principles of electrical capacitance tomography, based on the given preconditioned conjugate gradient method and calculation formula of the iteration steps of the ECT and to explore the feasibility of application of the algorithm, the algorithm to meet the convergence conditions and the reconstruction image error. Experimental results and simulation data indicate that the algorithm can provide high quality images and favorable stabilization compared with LBP，conjugate gradient algorithms in simple flow pattern and this new algorithm presents a feasible and effective way to research on image reconstruction algorithm for Electrical Capacitance Tomography System.

Abstract: The object of this paper concerns with the research of 8-electrode oil-water two-phase flow electrical capacitance tomography system. The distribution models of sensor’s field are established by the finite element method for the influence of the parameters of sensor’s structure on the performance of sensor. The analyses of simulation and experiment and the sensor’s optimization design are done, and the measure function of sensor’s optimization design is proposed based on sensor parameters that are listed as follows: length of electrodes, stretch angle of electrodes, thickness of pipeline, permittivity, thickness of stuff filled between screen and electrodes, radial electrodes and so on. In conclusion, the final parameters and materials adopted are proved better than those adopted before. Consequently the sensitivity and uniformity of the sensitive field is improved and the design of the measurement circuit is easier, and the data precision of sensitive field is enough for image reconstruction.

Abstract: In this paper, we propose a dynamic Electrical Capacitance Tomography (ECT) image reconstruction algorithm based on the extended Kalman filter (EKF) to estimate the rapidly time-varying changes in the permittivity within the time taken to acquire a full set of independent measurement data. The ECT inverse problem is formulated as a state estimation problem in which the system is modeled with the state equation and the observation equation. Computer simulation with synthetic data is provided and comparison is done with existing modified Newton Raphson (mNR) method to illustrate the reconstruction performance of the proposed algorithm.