Research On Signal Processing Method Of Ultrasonic Gas Flowmeter

Currently,the threshold method zero crossing detection is widely applied in gas ultrasonic flow meter.This signal processing method has high accuracy but it is sensitive to low SNR signal and often cause wrong recognition of zero crossing point.How to solve this problem is now a hot issue in signal processing.This paper intends to design a gas ultrasonic flow meter and present a method of signal processing on echo.In hardware design module,the square driving waves are modulated into waves with positive and negative amplitude through pulse transformer and then modulated into sine-like waves to drive the ultrasonic transducer.After pre-processing,echo waves are amplified and then transformed into pulses by zero crossing detection circuits for time measurement.The measurement circuits of peak voltage can acquire peak amplitudes of echo waves for further signal processing.In signal processing module,the mixed index module of echo waves is introduced and the characteristics of the echo peak under different working conditions are studied.Then a new signal processing method called variable ratio threshold method is proposed.The method can recognize the two adjacent peaks.The threshold voltage is set at middle of two peaks.Wrong zero crossing point can be recognized and compensated.Contrasting experiments between the variable ratio threshold method and the classical fixed ratio threshold method are done under different working conditions.The experimental results show that the new method has better performance than the traditional method.