A new characteristic peaks group judgement method for the accurate measurement of time‐of‐flight in the ultrasonic gas flowmeter

Abstract

As a typical method for calculating time-of-flight (TOF), the double-threshold method is widely applied in many time-difference-based ultrasonic gas flowmeters. However, the cycle-skip phenomenon caused by noises and various flowrate often affects the accuracy and reliability of flowmeters. Based on traditional double-threshold method and other improved double-threshold methods, a new characteristic peaks group judgement method is proposed for calculating TOF in this work. In this method, the peak's characteristics of the received signal are used to find the feature point which is stable in different flowrates. Then, based on the feature point, zero-crossing detection is executed for calculating TOF. In order to evaluate the new method, it is compared with traditional double-threshold method and the similarity judgment-based double-threshold method through offline tests on both simulated signals and real-flow signals. Results show that the proposed method can effectively eliminate the cycle-skip phenomenon and has higher precision and reliability than other methods. Furthermore, a digital signal-processing-based ultrasonic gas flowmeter with this method was implemented. Three calibration experiments were carried out on a gas flow standard device. The calibration results show that the flowmeter can achieve accuracy of class 1 in a wide velocity range from 1 to 35 m/s.

Design of ultrasonic flowmeter for wet gas measurement

“…According to different principles, the TOF measurement method can be divided into the cross-correlation method [7], the model method [8] and the threshold method [9][10][11][12][13]. For the first two methods, the calculations are complex which leads to poor real-time performance.…”

“…In 2021, in order to solve the problem that the traditional double threshold method was prone to cycle skip, Zheng et al proposed a new characteristic peak judgment method. The method searched for the stable peak point of the received signal in different flows as the characteristic point, and then used zero crossing detection to calculate TOF [13].…”

Time Delay Study of Ultrasonic Gas Flowmeters Based on VMD–Hilbert Spectrum and Cross-Correlation

“…The Cross-Correlation method calculates the correlation function of the forward and reverse echo signals and determines the signal delay from its maximum [ 17 ]. The thresholding method is a simple and fast technique, but it is more susceptible to misjudgment [ 15 , 18 ]. The feature point method needs to be fitted according to the signal contour and peak points, and the feature parameters need to be calculated for each device, which involves a large amount of computation.…”