In this article, the measuring methods of open channel discharge are presented, and an ultrasonic open channel flowmeter is designed, which is made up of measuring flume or weir, ultrasonic sensors and secondary instrument. The circuits of transmitting ultrasonic, receiving ultrasonic and compensating temperature are detailed. The time error is eliminated basically by a series of echo signal processing, including preamplification, band-pass filtering, programmable amplification, envelope detection, differentiation, zero-crossing detection, and monostable triggering. At the same time, the sonic velocity is revised by temperature compensation circuit, and the software is developed by modular design method. According to the schemes, an ultrasonic open channel flowmeter based on AT89S52 is designed successfully, which has higher precision, higher reliability and better cost performance.
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