The Research Of Signal Processing Method Based On Dual-threshold Method Of Transit-time Ultrasonic Flowmeter

With the rapid development of IC technology, there has been a great deal ofinterest in applying the ultrasonic method to flow measurement. As the ultrasonicflowmeter in our country started later, at present the ultrasonic flowmeter research andthe production of our country is still backward. Cooperated with ZheJiang Diyuaninstrument Co.,Ltd, we research the ultrasonic waveform and signal processingmethod for transit-time ultrasonic flowmeter development. The paper regards thetransit-time ultrasonic flowmeter as main research object, and proposes the signalprocessing dual-threshold method based on the research at home and abroad and thetheoretical analysis. The feasibility of this method is verified to improve the precisionand stability of the transit-time ultrasonic flowmeter.Firstly, the significance of flowmeter and the development of ultrasonicflowmeter are introduced in the dissertation. Then the paper introduces the state of thetransit-time ultrasonic flowmeter at home and abroad, and also presents the difficultyand significance of this thesis.Then the paper applies some normal signal processing methods to transit-timeultrasonic flowmeter. It firstly introduces the principle of the transit-time ultrasonicflowmeter and ultrasonic signal model. Then it analyzes the theoretical errors oftraditional threshold method, the least mean square (LMS) method and the unscentedKalman filtering (UKF) method. It shows that the three methods produce large errorsbecause of bad waveforms, so the paper puts forward a new dual-threshold processingmethod based on the signal characteristics of transit-time ultrasonic flowmeter.Finally the paper described in detail from four aspects of the theoretical analysisof dual-threshold method, system hardware design, system software design andfeasibility experiments verification of dual-threshold method:Firstly, the paper introduces the signal processing method and the design schemeof the present system. The proposed dual-threshold method is analyzed in theory.Then the design requirements of the system, the system transducer selection, the influence of the drive signal to the ultrasonic signal, the drive signal selection and theworkflow of the system are introduced in the paper.Secondly, the paper presents the hardware system including the hardwarestructure and modules to realize the method. The system is composed of amicroprocessor module, driver module, a timing conversion module, an analog signalprocessing module, a digital signal processing module, a high precision timingmodule, the data acquisition interface module and a power module. The principle ofeach module is introduced in detail.Thirdly, the paper introduces the software of the system. It focuses on judgingwhether the signal normal or not, and then calculating flow rate under normal signal.At last upload them to the host machine.Fourthly, the system platform has been completed to verify the feasibility of thismethod through data acquisition and the error analysis of the method.The dual-threshold method is innovated in the thesis, by which the system judgeswhether the signal normal or not, then calculate flow rate. The experiment is done toverify the feasibility of this method. This will be a good foundation for the furtherdevelopment of transit-time ultrasonic flowmeter based on dual-threshold method.