| The ultrasonic Doppler flowmeter which has the advantages of non-contact mounting,no flow resistance,no pressure loss,is suitable for detecting the non-pure fluid with bubbles and impurity particles.In the field of agricultural irrigation,the fluid is cloudy and the requirements of precision for measurement is limited,so that the ultrasonic Doppler flowmeter is proposed for agricultural irrigation.Based on the CFD simulation software Fluent to build irrigation motor-pumped wells 90° bend water pipeline simulation model,and the results were found by calculation,due to the abrupt change in the direction of operation,the fluid appears to be a secondary flow phenomenon,the velocity of the center of the pipeline is very different from the actual average velocity,uneven flow field influences the accuracy of ultrasonic Doppler flowmeter.Given the limited actual length of pipeline,the ultrasonic transducer is installed in the position of 6 times diameters or longer to ensure accuracy of measurement.The 32-bit STM32 with high performance ARM kernel is the main control chip for hardware circuit and program to design flowmeter,including high frequency sine wave emission circuit and echo signal filter amplifying circuit.Digital signal filtering based on LMS adaptive digital filter,and the frequency value was get by the fast Fourier transform.Build pipeline model to carry out the real flow test in the laboratory,selecting the electromagnetic flowmeter with 0.5 level as the standard meter to analyze test data.The flowmeter is tested and recorded by the variable frequency motor given different initial velocity,the ultrasonic Doppler flowmeter measurement data and the standard electromagnetic flowmeter data are based on the least square method to obtain the correction function.The function is applied to the flow calculation program to further improve the measurement accuracy. |
PDF Full Text Request