基于回波信号相似度的气体超声流量计动态阈值法研究

基于双阈值法的气体超声流量计采用第1阈值检测和过零检测确定回波的到达时刻点,然而由于回波波形易受工况环境因素的影响,会导致第1阈值错误,使回波到达时刻点发生错误偏移,影响测量精度,因此提出了一种基于回波信号相似度的动态阈值法。该方法获取回波信号极大值幅值后,计算设定工况和实际工况下回波信号上升区域部分的欧式距离以评估相似度,进而根据最大相似度确定阈值电压,实现阈值的动态调整,以确保回波信号到达时刻点的准确定位,实现飞行时间的准确测量。实验结果表明,该方法在不同工况环境下具有良好的适应性,样机的测量误差优于1%,重复性优于0.2%。

Study on Dynamic Threshold Method Based on Echo Similarity for Ultrasonic Gas Flow Meter

The first threshold detection and zero crossing detection are often used to determine arrival point of echo signal in the gas ultrasonic flow meter based on double threshold method.However,the echo wave is easily distorted caused by environment change,which lead to the first threshold wrong setting.As a result,the arrival point of echo will be shifted to the wrong position and the measurement accuracy will be affected.Therefore,a dynamic threshold method based on echo similarity is proposed.The several maximum amplitude of echo signal are obtained,the Euclidean distance of the rising area of the echo signal are calculated to evaluate the similarity.Then the threshold voltage is determined according to the maximum similarity to realize the dynamic threshold value.The correct threshold setting ensures that the accurate positioning of echo signal arrival time point.So the accurate measurement of flight time is obtained.Finally,the experimental results show that the method has good applicability under different working conditions.The measurement error of the prototype is better than 1% and the repeatability is better than 0.2%.