A Design Of Ultrasonic Flowmeter For Small Diameter

Flow measurement is becoming more and more important in industrial production and daily life for modern society.The application fields for flow measurement are very broad and the measuring methods are varied.As a new measuring method,Ultrasonic flowmeter has attracted many attentions for the significant advantages,such as non-contact measurement,less affected by the measured pipe size.etc.At present,the research and applications about ultrasonic flowmeter have made great progress at home and abroad, especially on the middle-size diameter flow measurement.It has been commercialized and achieved high accuracy.But under the large and small diameter application condition, ultrasonic flowmeter still needs furture study.On the basis of the characters for the small diameter ultrasonic flowmeter measurement,the π-measurement method is selected and its correction method is analyzed. A ultrasonic flowmeter with small diameter is designed based on the STM32F103microcontroller.Improvement approach are put forward in four aspects. In terms of the hardware filtering,a three stage ultrasonic receiving circuit is designed,consisting a preamplifier based on AD8228,a band-pass filter amplifier based on OP37,a programmable amplifier based on AD603.High SNR ultrasonic signal is achieved which signal peak is about0.8V and noise signal is about10mV.In terms of the timing resolution,a high-precision time-to-digital conversion chip TDC-GP21is used as high precision timing module.The highest time resolution can achieve22ps for TDC-GP21.In trems of detection logic, dynamic threshold method is introduced to detect the ZCP(zero crossing point) when the reception ultrasonic signal reach the first peak of the envelope which the ZCP and the peak are in the same cycle.Thus the influnce of noise on the detection can be reduced.In terns of digital filtering, in order to distinguish usefull signal and noise signal,wavelet decomposition to the ultrasonic propagation time signal for multiple scales and different levels is carried on by using ’db6’ function as mother wavelet with MATLAB software tool.Then filter process to the the ultrasonic propagation time signal is carried on by using wavelet threshold denoising method.Excellent filtering result is get. In the end,a ultrasonic flowmeter with small diameter is assembled and the control module is debugged.A experiment about ultrasonic propagation time measurement was accomplished and the time measurement accuracy is about0.5ns.The more larger for the flow,the more accuracy for the measurement.The highest accuracy can be reach2.6%.