基于FPGA的ECT系统设计

发布时间：2018-12-13 05:40

【摘要】：电容层析成像(Electrical Capacitance Tomography,ECT)技术,是一种通过测量空间介电常数分布来确定介质分布的技术,即通过检测非导电物场内介质分布变化引起的电容值变化,重建被检测的介质分布情况。与其他的检测技术相比,电容层析成像技术有着结构简单、成本较低、适用范围广、非侵入、安全性能好、无污染以及快速的测量响应等优点。随着工业信息化的不断发展,在电力、医学、石油等领域的生产过程中,特别是对两相流或多相流参数的实时在线检测领域,都具有广泛的应用和发展前景。本文研究的是基于现场可编程门阵列(Field programmable gate array,即FPGA)的ECT系统。本系统主要是由传感系统,数据采集系统以及成像计算机组成。传感系统用来将电介质分布转化为各极板对的电容值输出。数据采集系统用来获得不同角度的投影数据,然后通过数字正交解调方式对数据进行处理并传送给成像计算机。数据采集系统主要包含一块数据采集主板和一块数据采集开关板。其中,数据采集主板主要以FPGA为测量核心,以单片机为控制核心。数据采集开关板主要由开关通道选择电路、交流激励型C/V转换电路构成。数据采集开关板背面有8个测量通道,8个接地通道,即一共可测量8个电极板。成像计算机以MATLAB为软件平台,主要用来实现图像重建功能,即采用线性反投影算法(Linear Back Projection,简称LBP),根据采集来的投影数据,重建出传感器管道内的电介质分布情况,并显示在计算机屏幕上。本文主要介绍了电容层析成像技术在国内外的研究动态及发展现状,重点介绍了本系统所用到的关键性电路,即交流激励型C/V转换电路,分析了数字正交相敏解调方案的原理及优点,阐述了基于FPGA测量芯片,单片机控制芯片的数据采集系统的设计过程,并通过系统测试验证了该系统的可行性。最终,通过对系统进行测试,表明了该系统具有集成度高、稳定性好、信噪比高等优点;通过成像测试,表明该成像系统对传感器内部的介质分布可以呈现出相应的可视化图像。
[Abstract]:Capacitance tomography (Electrical Capacitance Tomography,ECT) is a technique to determine the dielectric distribution by measuring the distribution of dielectric constant in space, that is, by detecting the change of capacitance caused by the change of dielectric distribution in the field of non-conductive objects. Reconstruct the media distribution to be detected. Compared with other detection techniques, electrical capacitance tomography has the advantages of simple structure, low cost, wide range of application, non-invasive, good safety performance, no pollution and rapid measurement response. With the continuous development of industrial informatization, it has a wide application and development prospect in the fields of electric power, medicine, petroleum and other fields, especially in the field of real-time on-line detection of two-phase flow or multiphase flow parameters. In this paper, a ECT system based on field programmable gate array (Field programmable gate array,) is studied. The system is mainly composed of sensing system, data acquisition system and imaging computer. The sensor system is used to transform the dielectric distribution into the capacitance output of each plate pair. The data acquisition system is used to obtain the projection data from different angles, and then the data is processed by digital quadrature demodulation and transmitted to the imaging computer. The data acquisition system mainly includes a data acquisition board and a data acquisition switch board. Among them, the main board of data acquisition mainly takes FPGA as the measuring core, and the single chip microcomputer as the control core. The data acquisition switch board is mainly composed of switch channel selection circuit and AC excitation C / V conversion circuit. There are 8 measuring channels and 8 grounding channels on the back of the data acquisition switch board, that is, 8 electrode boards can be measured. The imaging computer uses MATLAB as the software platform, which is mainly used to realize the function of image reconstruction, that is, the linear backprojection algorithm (Linear Back Projection, is used to reconstruct the dielectric distribution in the sensor pipeline according to the collected projection data. And displayed on the computer screen. This paper mainly introduces the research trends and development status of capacitance tomography technology at home and abroad, and focuses on the key circuit used in this system, namely AC exciting C / V conversion circuit. This paper analyzes the principle and advantages of the digital quadrature phase sensitive demodulation scheme, expounds the design process of the data acquisition system based on the FPGA measurement chip and the single-chip microcomputer control chip, and verifies the feasibility of the system through the system test. Finally, by testing the system, it shows that the system has the advantages of high integration, good stability and high signal-to-noise ratio. The imaging test shows that the imaging system can present a corresponding visual image to the media distribution inside the sensor.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TP274.2;TN791

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