【作者】 王刚；

【导师】 颜华；

【作者基本信息】 沈阳工业大学 ， 工程硕士（专业学位）， 2019， 硕士

【摘要】 ECT技术(Electrical Capacitance Tomography,简称ECT)是一种基于电容敏感原理的电学层析成像技术。ECT技术可以对工业管道或者封闭的容器内的电介质进行可视化的测量,ECT技术的典型应用是对管道内的多相流进行实时监测。当管道内的各相组分浓度及其分布发生变化时,会引起多相流混合体介电常数的变化,使极板间的测量电容值随之发生变化。电容值的大小反映了多相流介质相浓度的大小和分布状况,从而可以通过测量各极板间的电容值就能得到管道内的介质分布信息。ECT技术具有结构简单、无辐射、非侵入性、响应速度快、成本低等优势。在野外等工作现场要求ECT系统具有工作性能稳定,集成度高,智能化,便于携带的特点。为此,本文将嵌入式系统与ECT技术相结合,研究基于Linux的嵌入式ECT系统。本文设计的嵌入式ECT系统主要由8电极传感器系统、投影数据采集系统、以及基于ARM开发板的图像重建单元组成。投影数据采集系统采用了信噪比高、抗干扰能力强的交流激励型C/V转换电路,并采用了不受初始相位影响且执行效率高、资源占用少的数字正交解调方案。在搭建好嵌入式Linux交叉编译环境后,编译配置了Linux内核,定制出嵌入式ECT专用系统。在嵌入式系统中设计串口通信程序实现采集数据与上位机的通信功能。编写了基于Qt的人机交互界面,用于控制传感器的数据采集、电容数据的归一化处理、以及图像重建。体现了嵌入式系统简单、便捷、高效的特点。本文研究了基于线性反投影算法的图像重建。利用多物理场耦合软件Comsol Multiphysics,建立了ECT传感器的有限元模型,获得了图像重建所需要的灵敏度矩阵以及两相流中常见的环状流、核心流、泡状流和层流所对应的投影数据。而后,在嵌入式图像重建单元中利用线性反投影算法对四种流型进行了图像重建,取得了较为理想的重建效果。本文对所建立的嵌入式ECT系统进行了实际测试。用在空心的PVC棒中加入石英砂的方法,模拟处于不同位置的核心流。测试结果表明该系统具有较好的实时性,能够实时检测出传感器内高介电常数区域的位置,具有应用在工业现场的潜力。本文工作有利于推动ECT技术的便携式应用。更多还原

【Abstract】 ECT technology(Electrical Capacitance Tomography,ECT for short)is an electrical tomography based on the principle of capacitive sensitivity.ECT technology allows for the visual measurement of dielectrics in industrial pipes or enclosed vessels.A typical application of ECT technology is the real-time monitoring of multiphase flows in pipes.When the concentration and distribution of the components in the pipeline change,the dielectric constant of the multiphase fluid mixture changes,and the measured capacitance value between the plates changes accordingly.The magnitude of the capacitance reflects the concentration and distribution of the phase concentration of the multiphase flow medium,so that the distribution information of the medium in the pipeline can be obtained by measuring the capacitance between the plates.ECT technology has the advantages of simple structure,no radiation,non-intrusive,fast response and low cost.In the field and other work sites,the ECT system is required to have stable working performance,high integration,intelligence,and portability.To this end,this paper combines embedded system and ECT technology to study embedded ECT system based on Linux.The embedded ECT system designed in this paper is mainly composed of 8-electrode sensor system,projection data acquisition system and image reconstruction unit based on ARM development board.The projection data acquisition system adopts an AC excitation type C/V conversion circuit with high signal-to-noise ratio and strong anti-interference ability,and adopts a digital quadrature demodulation scheme which is not affected by the initial phase and has high execution efficiency and low resource occupation.After setting up the embedded Linux cross-compilation environment,compile and configure the Linux kernel and customize the embedded ECT-specific system.The serial communication program is designed in the embedded system to realize the communication function between the collected data and the host computer.A Qt-based human-computer interaction interface is programmed to control sensor data acquisition,normalization of capacitance data,and image reconstruction.The entire process supports touch screens.It embodies the simplicity,convenience and efficiency of the embedded system.This paper studies image reconstruction based on linear back projection algorithm.Using the multiphysics coupling software Comsol Multiphysics,the finite element model ofthe ECT sensor is established,and the sensitivity matrix required for image reconstruction and the corresponding annular flow,core flow,bubble flow and laminar flow in the two-phase flow are obtained.Projection data.Then,in the embedded image reconstruction unit,the linear back-projection algorithm is used to reconstruct the four types of images,and the ideal reconstruction effect is obtained.In this paper,the embedded ECT system is actually tested.A core stream at different locations was simulated by adding quartz sand to a hollow PVC rod.The test results show that the system has good real-time performance and can detect the position of the high dielectric constant region in the sensor in real time,which has the potential to be applied in the industrial field.The work of this paper is conducive to the promotion of portable applications of ECT technology.更多还原