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.