针对传统的超声波多普勒流量计存在的精度低、稳定度差、动态响应慢的问题,研制了一种新型的超声波多普勒流量计。硬件部分主要设计了超声波换能器的发射与接收电路、功率放大与滤波电路、混频电路以及STM32F4及其外围器件。采用STM32F4作为超声波多普勒流量计的主控芯片,STM32F4采用Cortex-M4内核,其内置硬件FPU单元,在数字信号处理方面还增加了DSP指令集,使得它在数字信号处理方面的能力得到大大的提升。在硬件电路中选用高精度的DDS芯片产生基准信号来驱动超声波换能器。在频移信号处理方面,采用中频解调技术将频移信号解调到10 k Hz,提高了系统测量的稳定度以及对流速变化的响应速度。运用快速傅里叶变换算法(FFT)对STM32F4采集到的频移信号进行频谱分析,有效地提高了超声波流量测量系统的精度,并以matlab为分析工具对采集到的多普勒频移信号进行频谱分析,从而得到其频率的变化。
We propose a twin-array capacitance （TAC） sensor for the measurement of concentration, velocity, and flowrate of gas-solid two-phase flow. Using the sensitivity non-uniformity of a neighboring electrode, the regional concentration of the cross-section was reconstructed directly. Additionally, the finite element method was used to analyze the capacitance of the sensors composed of a different number of electrodes. TAC sensors with 4, 6, and 8 electrodes were found to be the best for regional concentration measurements. Based on this, the 8-electrode twin-plane electrical capacitance tomography （ECT） sensor, the 4-electrode TAC sensor, and the 6-electrode TAC sensor were used to measure the concentration, velocity, and fiowrate of granules in granular flow. The flowrates measured by ECT and TAC were compared with the flowrate obtained by a gravity sensor to verify the measurement accuracy. Experiments on vertical and inclined pipelines with granular flow were carried out. We found that the flowrate accuracy of the 4-electrode TAC is distinctly better than that of the 6-electrode TAC in the vertical pipeline while the flowrate accuracy of the 4-electrode TAC and the 6-electrode TAC were similar for the inclined pipeline.
