Time of Flight Measurement Method Combining Threshold Method and Cross-Correlation Method

Abstract

With various benefits such as a large range ratio, suitability for large-diameter measurement, and lack of excess pressure drop, ultrasonic flowmeters (UFMs) have been widely adopted in natural gas measurement. The accuracy of flow measurement in transit-time UFMs is mostly dependent on the accurate measurement of time of flight (TOF). The threshold method, the cross-correlation (CC) method, and the model-based method are examples of traditional TOF calculation techniques. However, the threshold method is susceptible to such factors as waveform distortion, amplitude attenuation, and noise, the CC method is constrained by the sampling frequency, and the model-based method necessitates a significant investment in calculation time and resources. Based on the analysis of the shortcomings of traditional TOF measurement methods, a TOF measurement method that combines the threshold method and CC method is presented. This method integrates the advantages of the high measurement resolution of the threshold method and the strong robustness of the CC algorithm. The results demonstrate that the flow rate accuracy and the repeatability of the TOF are greatly improved by this method.