Study On Gas Ultrasonic Flow Meter Algorithm Based On Fitting Correlation Method

Natural gas is a valuable non-renewable energy and a key component in the global energy market.Accurate measurement of natural gas is the basis and guarantee for efficient utilization of energy.In the field of natural gas detection,the time difference gas ultrasonic flowmeter has been applied with the advantages of high measurement accuracy and no pressure loss.However,it is difficult to apply the ultrasonic gas flowmeter in practice because of the short research time and immature core technology of the ultrasonic gas flowmeter in China.Especially for gas ultrasonic flowmeters with small pipe diameter,the measurement accuracy of transit time difference is often nanosecond level.How to improve the calculation accuracy of transit time difference under the condition of limited hardware sampling rate is of great significance for accurate flow measurement.In this paper,after the analysis of the current calculation methods of communication time difference at home and abroad,the main content is as follows:Firstly,this paper builds a data acquisition system.Through analyzing the echo signals collected under different flow rates,it is found that the propagation time difference is almost proportional to the flow rate.By taking 50 groups of data at each flow rate to analyze the peak stability of the cross-correlation waveform,found in a small cross-correlation peak flow interval is stable,but the correlation peak displacement under heavy traffic phenomenon,this paper discusses the phenomenon of echo power three cross-correlation processing method is proposed,and found that after processing each traffic cross-correlation peak can remain stable.Secondly,aiming at the calculation of time difference,the method of fitting cross correlation is proposed to improve the accuracy in this paper,the upstream and downstream echo waveforms are directly cross-correlated.By taking waveform cross-correlation peak with a little around each fitting a quadratic parabola and estimate of the parabola take maximum points as to determine the time points,so as to improve the calculation accuracy of time difference.The time difference calculated by the fit cross correlation method and the fitting threshold method is compared in several groups,and it is found that the fit cross correlation method can calculate the stable and high precision time difference under various flow rates.Finally,in order to verify the effectiveness of the signal processing method,a sonic nozzle gas meter calibration device is used to calibrate the airflow.The flow points of the experiment included:0.0405 m~3/h、0.1248 m~3/h、0.1990 m~3/h、0.4046 m~3/h、0.6016 m~3/h、1.1873 m~3/h、2.4236 m~3/h、4.2440 m~3/h and 5.9986 m~3/h.The experimental results show that the indication error and repeatability obtained by the fitting cross-correlation method in different flow ranges meet the requirements of the national standard.