Research Of Gas Ultrasonic Flowmeter Based On Cross-correlation Algorithm Of Piecewise Envelope

As a kind of efficient and clean energy,natural gas has received more and more attention in recent years,and its demand is huge.Accordingly,natural gas metering instruments will develop rapidly.Gas ultrasonic flowmeter occupies an important position in the field of gas flow detection because of its wide range,high precision,no pressure loss and many other advantages.It is of great strategic significance to develop a gas ultrasonic flowmeter with high performance and reliability.There are many kinds of time delay estimation methods for gas ultrasonic flowmeter.Cross-correlation algorithm has been widely used because of its strong anti-interference ability and high accuracy.The premise of accurate time delay estimation of cross-correlation algorithm is that the whole envelope of the received signal is consistent under different conditions.However,the signal envelope changes randomly under complex conditions such as large traffic,which seriously affects the accuracy and reliability of time delay estimation of cross-correlation algorithm.How to improve the stability of signal envelope in complex environment is the first problem to be solved in the study of time delay estimation of cross-correlation algorithm.In this paper,a time delay estimation method based on piecewise envelope cross-correlation algorithm is proposed.By guaranteeing that the signal envelope is basically consistent under different conditions,the problem of inaccurate flow calculation caused by unstable signal envelope in cross-correlation algorithm is solved.The main research contents are as follows:(1)Study on the excitation mode of piecewise envelope and the envelope characteristics of received signal.Based on the oscillation characteristics of the transducer,a piecewise envelope excitation method is proposed by observing and analyzing a large number of experimental phenomena and combining the research progress at home and abroad.The simulation and experimental results show that the piecewise envelope excitation method can obtain the received signal waveform with obvious characteristics,and the overall envelope consistency of the received signal is good.(2)Design of cross-correlation algorithm for piecewise envelope.Based on piecewise envelope excitation scheme and traditional cross-correlation algorithm,a cross-correlation algorithm based on piecewise envelope excitation scheme is proposed.The verification results show that the cross-correlation algorithm based on piecewise envelope excitation scheme greatly improves the accuracy of cross-correlation transit time measurement.In addition,the measurement accuracy is further improved through the selection of reference waveform,the interception of calculation waveform,the pre-processing of calculation waveform and the acquisition of high-precision transit time.(3)The overall design and hardware and software design of the piecewise envelope cross-correlation flow measurement system.The hardware design mainly completes the power module design,the excitation circuit module design,the receiving circuit module design,the signal acquisition module circuit design;the software design mainly completes the main program,the initialization program,the data acquisition program and the flow measurement program design.Software system and hardware system cooperate to form a complete flow measurement system.(4)Verification of flow calibration experiment.According to the design scheme,the prototype was made and the flow calibration experiments were carried out under different working conditions.The calibration results show that the piecewise envelope cross-correlation algorithm can solve the problem of inaccurate measurement caused by unstable signal envelope in complex environment such as large flow,and has certain research value.