Design And Realization Of External Clamp Ultrasonic Flowmeter Based On Cross-correlation Method

As a flow measurement tool,ultrasonic flowmeter is not only widely used in industrial and agricultural production,but also plays a very important role in the development of aerospace industry.However,in the practical application of ultrasonic flowmeters,the measurement accuracy and measurement range often limit the scope of its use.Combined with the research status and development trends of the same type of ultrasonic flowmeters at home and abroad,specific indicators are proposed and related researches are carried out.This paper mainly studies the following contents:（1）The theoretical basis of ultrasonic flow measurement is studied.It mainly deduces the measurement principle of the time difference method,the correlation theory of the crosscorrelation method,the influencing factors of the flow measurement accuracy and the selection basis of the ultrasonic transducer.（2）Carry out the modeling,simulation and analysis of ultrasonic flow measurement.Through COMSOL finite element modeling and simulation,the background flow under different fluid states is analyzed,and the influence of pipe diameter,pipe material,ultrasonic signal frequency,transducer installation angle and transducer installation method on ultrasonic signal propagation is analyzed.The implementation process of the cross-correlation algorithm is simulated by Python software,which lays the foundation for the subsequent application of the cross-correlation algorithm.（3）The ultrasonic flow measurement system scheme is designed.By analyzing the shortcomings of the traditional forward and reverse flight time difference measurement scheme,and combining with the specific index requirements,a forward and reverse flow time measurement scheme based on the cross-correlation method is proposed.A combination of embedded microprocessor and FPGA is designed,which can give full play to their respective advantages and improve the operating efficiency of the system;a signal driving and processing circuit is designed to drive the ultrasonic transducer,process the echo signal,record the flight time and record the echo waveform.（4）A set of ultrasonic flowmeter test platform was built to test and analyze pipes with pipe diameters of DN15,DN26 and DN55 respectively.The test results show that the error of flow indication under different pipe diameters and different ball valve openings is all within 1%.Within the range,the measured flow velocity is a minimum of 0.11m/s and a maximum of2.96m/s,which meets the design requirements.