Ultrasonic Flow Measurement And Monitoring Software Design Based On Cross-correlation Method

In recent years,with the increasing scale of process industry production,the application of ultrasonic flowmeters has become more common,and the requirements for its measurement accuracy have also continued to increase.In the ultrasonic flow measurement,the measurement accuracy of the d To F directly determines the performance of the flow measurement.The traditional measurement method detects the first wave of the echo signal through threshold comparison to calculate the d To F.Because the amplitude of the echo signal is affected by many factors,it will continue to change during the long-term measurement process,and the amplitude of the first wave is small and reliable.The low noise ratio and susceptibility to interference make the first wave detected by threshold comparison prone to misdetection or the phenomenon of waveform dislocation,which leads to huge deviations in the d To F measurement,and severely reduces the measurement accuracy.Therefore,this article focuses on the study of ultrasonic flow measurement methods around the measurement of the d To F.This paper uses the cross-correlation method that is only related to the signal similarity,is less affected by the echo amplitude and has good stability to measure the d To F.First,a high-speed analog-to-digital converter is used to sample the echo signals received by the upstream and downstream transducers,and then cross-correlation calculations are performed on the upstream and downstream discrete echo signals obtained by the high-speed sampling.Because of the large amount of calculation of the cross-correlation function,it is difficult to directly apply to conventional embedded microcontrollers.Therefore,this paper adopts discrete convolution operation to realize discrete cross-correlation function operation.In order to reduce the amount of calculation,the fast fourier transform is used to convert the upstream and downstream discrete echo signals to the frequency domain,and the time domain convolution operation result is obtained through the frequency domain product operation and the fast fourier inverse transform,thereby obtaining the cross-correlation discrete output of the function.Since the delay time corresponding to the maximum point of the cross-correlation function output is the d To F between the upstream and downstream echo signals,based on the discrete output of the cross-correlation function,the cubic spline interpolation method is further adopted to obtain the continuous output fitting curve of the cross-correlation function,and obtain the d To F measurement result by obtaining the delay time corresponding to the maximum point of the fitted curve.Based on the actual echo signal sampling data of the DN100 pipe segment ultrasonic flowmeter,this paper uses Matlab to carry out the simulation verification of the cross-correlation method to measure the d To F,and then completes the cross-correlation method embedded software and supporting monitoring of the upper computer based on the existing hardware of the research group software development.On the national standard verification line of an ultrasonic flowmeter in Qingdao,the experimental measurement of the cross-correlation method was carried out for the four pipe sections of DN50,DN100,DN150 and DN250 at different flow velocities.The comparison result with the standard flow velocity of the verification line shows that the cross-correlation method can effectively improve the accuracy and reliability of ultrasonic flow measurement.