Research On The Key Technology Of The High-accuracy Transit-time Ultrasonic Flowmeter

Ultrasonic flowmeter is becoming increasingly important in the field of liquid flowmeasurement, it played a pivotal role both in industrial production and daily life. The transit-timeultrasonic flowmeter has many outstanding advantages highly favored by domestic and foreignscholars, the main research hotspot is how to improve the the flowmeter measurement accuracyand stability. The dissertation discusses associated impacts about the time difference signalcharacteristics of ultrasonic flowmeter, and how to improve measurement accuracy and stability.Firstly, the dissertation made a detailed introduction to the measurement principle of thetransit-time ultrasonic flowmeter,and conducted both qualitative and quantitative analysis of thereasons that cause measurement errors.In which sound signal is the key for flow rate information inthe transit-time ultrasonic flowmeter, the accurate measurement of the time difference is thepremise of the ultrasonic flowmeter of high precision measurement. Therefore, article made asystematic study of factors affecting the measurement of the time difference, time differencemeasurement is mainly affected by the time measurement resolution ultrasound echo detection,signal delay and transducer performance. During the design process, choosing high-resolution timemeasurement chip to solve time measurement problems; For the problem of detection of the echosignal, the article used an echo signal processing and over zero threshold comparator circuit,it caneffectively detect the echo signal endpoint; Using channel switching technologies to overcome thesignal delay inconsistency problem; For the transducer performance asymmetry, the article solve thisproblem through a static zero calibration method. These measures laid the foundation to improvemeasurement accuracy and stability of the system.Secondly, the dissertation has done a detailed analysis of the collecting time difference data,respectively using the time domain and frequency domain signal processing method for processingon the time difference data, and in order to reduce the influence of noise, thereby improving themeasuring accuracy and stability of the flowmeter. The articles were selected weighted movingaverage filtering method and wavelet threshold denoising method to deal with the time differencedata, and comparative analysis of the effect of the two processing methods for the processing the time difference data of the ultrasonic flowmeter. Experiments show that wavelet transform can deal withthe ultrasonic flowmeter collecting data feasibility, and improve the flow meter measurement accuracy effectively.Finally, according to the characteristics of the ultrasonic flowmeter time differencemeasurement, the article uses the FPGA design time difference measurement module. In this paper,the design of time measurement module include the coarse measurement unit, precision measuringunit and data computing and storage unit. the article gives a detailed design principles of each unit,and the simulation results show that the time measurement circuit design has basically reached therequirements.