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Abstract：
The accuracy of ultrasonic flowmeter time delay measurement is directly affected by the processing method of the ultrasonic echo signal. This paper proposes a method for estimating the time delay of the ultrasonic gas flowmeter based on the Variational Mode Decomposition (VMD)-Hilbert Spectrum and Cross-Correlation (CC). The method improves the accuracy of the ultrasonic gas flowmeter by enhancing the quality of the echo signal. To denoise forward and reverse ultrasonic echo signals collected at various wind speeds, a Butterworth filter is initially used. The ultrasonic echo signals are then analyzed by Empirical Mode De-composition (EMD) and VMD analysis to obtain the Intrinsic Mode Function (IMF) containing distinct center frequencies, respectively. The Hilbert spectrum time-frequency diagram is used to evaluate the results of the VMD and EMD decompositions. It is found that the IMF decomposed by VMD has a better filtering performance and better anti-interference performance. Therefore, the IMF with a better effect is selected for signal reconstruction. The ultrasonic time delay is then calculated using the Cross-Correlation algorithm. The self-developed ultrasonic gas flowmeter was tested on the experimental platform of the gas flow standard devices using this signal processing method. The results show a maximum indication error of 0.84% within the flow range of 60-606 m3/h, with a repeatability of no more than 0.29%. These results meet the 1-level accuracy requirements as outlined in the national ultrasonic flowmeters calibration regulation JJG1030-2007.
摘要：
超声回波信号的处理方法直接影响超声流量计时延测量的精度。本文提出了一种基于变分模态分解（VMD）-希尔伯特谱和互相关（CC）的超声气体流量计时延估计方法。该方法通过增强回波信号的质量来提高超声波气体流量计的精度。对在各种风速下采集的正向和反向超声回波信号进行去噪，最初使用Butterworth滤波器。然后通过经验模式去成分（EMD）和VMD分析来分析超声回波信号，以获得包含不同中心频率的本征模式函数（IMF）。分别。希尔伯特谱时频图用于评估VMD和EMD分解的结果。结果表明,VMD分解得到的IMF具有较好的滤波性能和较好的抗干扰性能。因此,选择效果较好的IMF进行信号重构。然后使用互相关算法计算超声时间延迟。利用该信号处理方法在气体流量标准装置实验平台上对自行研制的超声波气体流量计进行了测试。结果表明，在60-606m3/h的流量范围内，最大指示误差为0.84%，重复性不超过0.29%。这些结果满足国家超声波流量计校准法规JJG1030-2007中概述的1级精度要求。
