Design And Experiment Study On Network Multi-path Ultrasonic Gas Flowmeter

Because of the advantages of high measurement accuracy and non-contact measurement,ultrasonic gas flowmeters are widely used in the measurement of natural gas,coal gas and oil gas flow.According to the number of acoustic paths,ultrasonic gas flowmeters can be divided into single-path flowmeters and multi-path flowmeters.At present,the domestic ultrasonic gas flowmeters are mainly single-path flowmeters,while the multi-path ultrasonic gas flowmeters with mature technology are scarce.Transit-time ultrasonic gas flowmeters are the most widely used flowmeters.Their principle is to obtain the flow rate information of gas by measuring the downstream and upstream transit time of ultrasonic in gas,so as to obtain the flow rate of gas.According to the measurement principle of transit-time method,increasing the acoustic path can effectively improve the measurement accuracy of transit time.At the same time,using high voltage to excite the ultrasonic transducer can obtain stronger ultrasonic excitation signal,enhance the anti-interference ability of the signal,and improve the signal-to-noise ratio.Based on the above two reasons,a network four-path ultrasonic gas flowmeter prototype with two primary and two secondary reflection acoustic paths is designed and manufactured,and the corresponding high-voltage driving circuit module is designed to drive the ultrasonic transducer.In addition,the performance of the designed flowmeter prototype is studied by experiment.The main work and innovations of the thesis are as follows:1.A kind of network flow sensor is designed based on the reflection acoustic path.The relationships between the intensity of the ultrasonic echo signal and the excitation voltage,and between the intensity of the ultrasonic echo signal and the acoustic path are studied.The feasibility of designing flowmeters with reflective paths is verified by the primary and secondary reflection experiments.2.The high voltage drive circuit module is designed and manufactured.The high voltage driving circuit includes transmitting and receiving circuit,acoustic path selection and switching circuit,which can generate a driving voltage of±100 V at most and can alternately excite 8 ultrasonic transducers.Based on the sensor and high-voltage driving module,the corresponding network four-path ultrasonic gas flowmeter prototype is developed and the ultrasonic gas flow measurement experimental system is built.3.The experimental study on the designed network flowmeter prototype is carried out.Firstly,taking the standard deviation of transit time as the index,experimental study is carried out in straight pipe,downstream of 90° single bend(5 D and 10 D)and downstream of 180° double bend(5 D and 10 D),respectively.The experimental results show that the maximum standard deviation of the four channels is 1.7597 us,which shows that the four acoustic paths have good measurement stability,thus verifying the feasibility of the network flowmeter prototype designed in this thesis.Then,the flow field distribution coefficient is introduced to quantitatively analyze the velocity and flow field distribution in the pipeline.Finally,taking the amplitude offset of the received waveform as the index,the characteristics of the ultrasonic received waveform in the elbow flow field are studied.The experimental results show that the amplitude offset increases with the increase of the flow rate,reaching 40%at the frequency of 50 Hz,which shows that the distortion of the ultrasonic received waveform is serious in the elbow flow field.