Design Of ECT System Based On FPGA

Electrical Capacitance Tomography(ECT) is a kind of technology by measuring spatial distribution of dielectric constant to determine the distribution of media, and it can detect variation of capacitance values which are caused by the changes in the distribution of non-conductive media. Finally, distribution of the detected medium is reconstructed. Compared with other detection techniques, ECT technique has lots of advantages, such as simple structure, inexpensive, wide range of application, non-invasive, safety, no pollution and fast response time, etc. With the continuous development of the information industry, it has been used in the petroleum, power and medical industries, especially for two-phase flow and multi-phase flow parameters real-time online detection field with a wide range of applications and development prospect.In this paper, the system is mainly composed of a sensor system, data acquisition system and a computer imaging system. The dielectric distribution is changed into capacitance to output by the sensor system. Data acquisition system is utilized to obtain the projection data of different angle, process data with digital orthogonal demodulation and transmit the data to the computer imaging system. Data acquisition system is composed of a data acquisition board and a data acquisition switches board. Among them, in the data acquisition board, FPGA is mainly taken as the core of measurement and the SCM is regarded as the control core. The data acquisition switch board is mainly composed of multi-channel selection circuit and AC-based C/V converter circuit. There are eight measurement channels and eight ground channels on the back of the data acquisition switch board. It means that switch board can detect a total of eight measure electrode plates. Computer imaging system based on MATLAB is mainly used to realize the image reconstruction function, and the Linear Back Projection is applied to the software. According to the collected projection data, the reconstruction of dielectric distribution inside the capacitance sensor can be accomplished on a computer screen.This paper mainly introduces the research trends and development status of electrical capacitance tomography technology at home and abroad. The fundamental circuit of the system is introduced in this paper, namely AC-based C/V converter circuit. The principle and advantages of digital orthogonal demodulation project is analyzed in this paper. It describes the design process of a data acquisition system based on FPGA measurement chip and single-chip which is taken as micro-computer control chip in this paper. And the feasibility of the system is checked by experiments. Finally, through the system test, it shows that the system has high integration, good stability, high SNR, etc. By imaging test, it shows that the imaging system of the medium distribution within the sensor can present a corresponding visual image.