Research Of Driving And Receiving Circuit Of Low-Power Gas Ultrasonic Flowmeter Based On Matching Network

Ultrasonic transit time flow meters for gas(USMs)has already taken over in the natural gas metering market,because of its high accuracy,wide range of measurement and easy maintenance.As a part of transmitting and receiving ultrasonic signal as well as realizing electrical and acoustic signal conversion,ultrasonic transducer plays a crucial role in natural gas flow metering.During the application of flowmeters,a series of problems occurs such as redundant power consumption,low excitation efficiency unstable output voltage and so on caused by the different load characteristics between transducer and ultrasonic signal source,which will influence measurement accuracy and reliability of the flowmeter.As a result,the impedance matching of transducers has always been the focus of research recently.However,the resonance frequency of transducer will drift under the change of external environment causing traditional static impedance matching no longer working.Based on this phenomenon,dynamic impedance matching method is proposed in this paper to improve measurement accuracy,and meanwhile design the whole circuit of low-power gas ultrasonic flowmeter.The main substance is described below:Firstly,based on the analysis of the ultrasonic transducer's equivalent circuit,its behavior under the change of external environment was studied.The series matching network and parallel matching network were compared.Aiming at solving problems caused by static matching method,two dynamic matching schemes were proposed and studied,and finally auto-tracking of resonance frequency was chosen in this paper.Based on this method,the whole circuits including the transmitting and receiving circuits for low-power gas ultrasonic flowmeter was designed.Secondly,each module of the whole circuits was designed.Low-power control module and high-precision timing module circuit were composed of MSP430 and TDC-GP2 Chips separately.In transmitting circuit,high frequency transformer was designed to boost the voltage.In frequency tracking module,zero-crossing method was employed to detect the phase difference signal of voltage and current.Based on the dual threshold method,all signal processing modules of receiving circuit design was finished to obtain high precision timing.Thirdly,after the hardware design of ultrasonic circuit system,main measurement program,frequency dynamic tracking program and flow measurement program was completed.And in frequency dynamic tracking program,different adjustment methods are proposed to deal with the sudden change and slow drift of resonance frequency.Lastly,after all the hardware and software design,simulation experiments were carried out on the basis of Pspice software.Under the application of ultrasonic gas flowmeter prototype developed by our team,various tests on experimental platform are conducted to validate the feasibility of the whole design.