The Research Of Ultrasonic Gas Flowmeter Based On MSP430

Compared with traditional gas flow meter,ultrasonic gas flow meter has the advantages such as non-contact measurement and simple structure.But it also has some weakness such as low accuracy,diffcult to design the dirving circuit for the ultrasonic sensor and low signal-noise ratio.In this paper,a new method to designe gas flow meter is poposed.The news gas flow meter developed based on this method can overcome the shortcomings and has the advantages of high accuracy,ultra-low power consumption and high signal-noise ratio.This paper describes the history of the development of flowmeter,briefly introduces the a variety of current commonly used gas flowmeter,focuses on the working principle and characteristics of ultrasonic gas flowmeter,and put forwards the overall design scheme of a new type of ultrasonic gas flowmeter.An ultrasonic sensor with the centre frequency of 120 KHz and driving voltage 300 V is made by the requirement of us.Z type sensor arrangement and time difference method is used to achieve the flow measurement.The MSP430F149 MCU outputs +3.3V amplitude pulse,then max4426 is used as level driving and the field effect tube is used to realise power amplifier.Finally,a 10:100 transformer is used to complete the design of the driving circuit for ultrasonic sensor.The amplitute of output signal from the ultrasonic sensor is about tens of millivolt to hundreds of millivolts.In order to improve the signal-to-noise ratio and reduce power consumption,a single power supply OP primary amplifier circuit is designed,operational amplifier type is max4331,and the midpoint voltage method is used to realize negative signal amplification.In order to filter the noise of the primary amplifier circuit,a two order band-pass filter with center frequency of 120 KHz is designed.While different diameter and other reasons lead to ultrasonic sensor output signal with different amplitute,an adjustable gain inverting amplifier circuit is designed based on digital potentiometer to ensure output signal peak to peak value 2.7V in any case.The MAX998 comparator is used to design the comparison circuit,and the output of this circuit is used to measure the time intreval.In order to obtain a higher time resolution,a dedicated time chip TDC-GP2 is used,whose time resolution can reach 50 ps.Finally,the principle and equipment of gas flowmeter calibration system are briefly described,and the calibration data are analyzed.The experimental results show that the developed prototype meets the design requirements.