电容成像传感器优化设计及其试验研究

Optimal Design and Experimental Study of Capacitance Imaging Sensor

关键词:  电容层析成像  图像重建  现场可编程门阵列  传感器优化  信噪比

Key words:  Electrical capacitance tomography  Image reconstruction  FPGA  Sensor optimization  Signal to noise ratio

摘要:

为了减小电容层析成像（Electrical Capacitance Tomography,ECT）传感器相邻极板间耦合电容引起电容测量时的噪声值，设计了差分电极传感器系统并对差分电极与测量电极距离进行参数优化。实验系统采用现场可编程门阵列（Field Programmable Gate Array,FPGA）直接数字频率生成模块生成数字量的正弦激励信号，通过D/A转化为正负交流信号分别对测量电极和差分电极进行激励。差分电极与测量电极到管道中点的距离比例约1:1.2时传感器灵敏度最佳，仿真图像误差降低至0.23，图像相关系数提升到0.84；实验中空场时的系统平均信噪比比普通传感器提升了5.10dB，满场时的系统平均信噪比提升了4.50dB，相邻电极对的静止电容减少至38％，而电容变化占用最多测量值，即62％。差分电极传感器系统经过电极之间距离的优化设计，传感器系统性能得到提升，通过实验验证其可行性，并且能够应用在滑油监测。

Abstract:

In order to reduce the noise value of capacitance measurement caused by the coupling capacitance between adjacent plates of Electrical Capacitance Tomography (ECT) sensor, a differential electrode sensor system is designed and the parameters of differential electrode and measuring electrode distance are optimized. The experimental system uses Field Programmable Gate Array （FPGA） direct digital frequency generation module to generate digital quantity. The sinusoidal excitation signal is converted into a positive and negative alternating current signal by D/A to excite the measuring electrode and the differential electrode, respectively. The sensor sensitivity is best when the ratio of the distance between the differential electrode and the measuring electrode to the midpoint of the pipe is about 1:1.2, the error of the simulation image is reduced to 0.23, and the image correlation coefficient increased to 0.84. The average signal-to-noise ratio of the actual experimental hollow field increased by 5.10dB. The average signal-to-noise ratio of the system at full field increased by 4.50dB, the static capacitance of adjacent pairs is reduced to 38%, and the change in capacitance takes up the most measured value, or 62%.The differential electrode sensor system is optimized by the distance between the electrodes, and the performance of the sensor system is improved. The feasibility is verified by experiments, and it can be applied to the oil monitoring.