Design And Research Of Ultrasonic Flowmeter Based On FPGA

Ultrasonic flowmeters are flowmeters that use ultrasonics to measure fluid flow rates to calculate volume flow.With an ultrasonic transducer,the flow meter can obtain the measured time difference by ultrasonic pulse transmission and reception or by Doppler effect measurement of the frequency shift to measure the average velocity of the fluid along the ultrasonic transmission path.Compared with other flowmeters,ultrasonic flowmeters are less affected by the temperature,pressure,density,and conductivity of the fluid being measured,and have high measurement accuracy,and are easier to install and disassemble,and have lower maintenance costs.However,the price of ultrasonic flowmeters with relatively advanced technology in foreign countries is usually higher,which will increase the production cost of users.Therefore,it is very significant to conduct research on ultrasonic flowmeters.This thesis briefly introduces the development status of the ultrasonic flowmeter industry,the research purpose and significance of the topic,introduces the theoretical basis of ultrasonic science,and analyzes the working principle of different types of ultrasonic flowmeters.At the same time,the matching layer made of different materials was used for testing,and the influence of the matching layer on the ultrasonic signal was explored.This thesis puts forward an overall design scheme of ultrasonic flowmeter,which mainly includes the following parts: ultrasonic sensor module,middle measuring pipe segment module,ultrasonic wave transmitting and receiving module and upper computer module.The design of the middle measuring pipe section and the selection of ultrasonic sensors were completed.In this thesis,two different designs of ultrasonic signal processing units are proposed,which are a single-channel simultaneous transmission and reception of ultrasonic signals and multiple channels of alternating transmission and reception of ultrasonic signals.The hardware circuit design of each module of the two schemes is described in detail,the programming flow of the FPGA is completed,and its basic functions are tested.The single-channel simultaneous transmission and reception scheme has the advantage of good signal synchronization,but when two signals are transmitted at the same time,ultrasonic waves will be reflected more inside the pipeline,resulting in greater noise of the received signal,and the single channel has uneven flow velocity.The adaptability of the situation is poor;in theory,although the synchronism of the multi-channel alternating transceiver scheme is slightly poor,the use of the TDC series chip to compensate for the time-based detection of the received signal can be compensated,and the weighted processing of multiple groups of ultrasonic signals is more stable.After comparing the advantages and disadvantages of the two different methods,a multi-channel alternative to transmit and receive ultrasonic signals was finally adopted.This thesis completes the design of the upper computer based on Labview,realized the functions of user login,data processing and parameter setting.At the same time,the hardware and software testing was completed in the flowmeter calibration unit.After removing the environmental impact and fixed error,it can be timely.Within a certain range of flow rates,the error can reach 1%,which proves the feasibility of the ultrasonic flowmeter designed in this thesis.