The Research And Design Of Gas Flowmeter Based On Air-coupled Ultrasonic Sensor

With the development of human society,the global lock of energy and water resources is growing,so people in various fields are getting higher and higher requirements on the flow measurement.Correspondingly,the research and development of the flow measurement device has also accelerated.With the rapid growth of the ultrasound detection technology,Ultrasonic flowmeters,as an important instrument for flow detection,has become a bright spot in the field of flow detection in recent years.From the current application situation,ultrasonic flowmetes compared to other measurement equipment has its own unique advantages in the measurement accuracy,reliability,pressure loss,maintenance and manufacturing costs.Ultrasonic flowmeters can mainly divided into time difference method and Doppler effect method.The Doppler method can only detect impure fluids with particles,but the time difference flow meter does not have this limitation,so it is widely used.Ultrasonic flowmeters are rarely used in the field of gas flow detection because the attenuation of ultrasonic is very large when it spreads in the air.In this paper,a new type of air-coupled ultrasonic sensor is used to design a gas ultrasonic flowmeter with integrated time difference method and frequency difference method.Details are as follows:1.Check the relevant information at home and abroad to understand the design principle of ultrasonic flowmeter.A new type of air-coupled ultrasonic sensor is selected for the measurement of gas.The center frequency is 200 KHz.Under the excitation of peak and peak value of 10 V,it can receive 35 mV signal at 10 cm,which is much higher than other sensors.2.According to the design requirements,we use ARM chip STM32F407 to set up a system framework and complete the system hardware circuit design.We use the STM32F407 built-in analog-to-digital converter to generate sensor excitation signal.As the amplitude of the DAC generated signal is 0-3.3V,it can't directly stimulate the sensor to work,so we used ADA4700-1 to design an amplifier circuit to amplify the excitation signal.For the ultrasonic transmission loss is very large in the air,the sensor received signal is very weak,this paper designed a magnification adjustable circuit to amplify the signal with AD8421.This paper also designed a band-pass filter with AD8066 to weaken the noise signal in the circuit and improve the signal to noise ratio.The collection range of the built-in ADC is 0-3.3V,so we designed the corresponding bias circuit with AD8066 to adjust the amplitude of the signal.3.We completed the system software design with STM32F407 as the control chip.It mainly includes the generation of excitation signals,the collection of received signals,flow display on the OLED and data storage.At the same time,we use the chip's digital signal processing library function to further processing and calculation of the signal and complete the flow measurement.4.The experiment of time difference flow detection is carried out by using the designed system,and the data are analyzed and summarized.