A Novel Differential Time-of-Flight Algorithm For Highprecision Ultrasonic Gas Flow Measurement

Ultrasonic flow meters have been widely used in many fields with their unique advantages such as non-contact,small pressure loss,high measurement accuracy,and large range ratio.In the field of natural gas measurement,ultrasonic gas flow meters have gradually replaced traditional mechanical flow meters and become instruments for legal settlement of natural gas trade.However,the research of ultrasonic gas flow meters started late in China,and there are still some technical problems.In the main test performance indicators,the accuracy and stability of measurement still need to be improved.This paper studied the related problems existing in the process of ultrasonic gas flow measurement,mainly including the research on the channel layout of ultrasonic gas flow meter,design of single and multi-path ultrasonic gas flow measurement experimental system,modeling and analysis of excitation and echo signal,research on high-precision algorithm processing of ultrasonic echo signal,and verification of experimental results,etc.In this paper,we focus on the measurement of single ultrasonic gas flow under small flow.A novel differential time-of-flight(TOF)algorithm for high-precision ultrasonic gas flow measurement is proposed.The main content of this paper are as follows:Firstly,several measurement methods of ultrasonic flow meter are studied,and different measurement methods of absolute TOF are analyzed.According to the pipe diameter of this study,a transit time ultrasonic gas flow meter with V-shaped pipe structure was designed,and the system experiment platform of single and multi-path flow meters was debugged.Secondly,the excitation and echo signal are modeled and analyzed,and the relationship between the measurement accuracy of absolute TOF and differential TOF to the ultrasonic flow measurement is obtained.Based on the research of the time-domain cross-correlation method,the frequency-domain cross-power spectrum method is proposed to process the up and down echo signals to obtain a highprecision differential TOF.Furthermore,the obtained flow rate is processed by filtering and meter coefficient verification,reducing the system error and reducing the repeatability of flow measurement.Finally,a gas calibration experiment was carried out using the standard calibration device of a sonic nozzle gas meter to verify the effectiveness of the proposed digital signal processing method and the system.The results show that the ultrasonic gas flow meter meets the error of zero drift at room temperature and high temperature;it has high accuracy under dynamic flow rate and reduces the repeatability error.