Design Of Ultrasonic Flowmeter Based On Time Difference Method

Flow measurement, whether in industrial production or daily life of all, has a significant role. Ultrasonic flowmeter is paid attention by many researchers for its non-contact measurement and wide measuring range. And time difference ultrasonic flowmeter as a very important one of ultrasonic flowmeters has the advantages of high accuracy, wide application and so on.Details of the time difference flow measurement of the basic principles were introduced. And the type, the generate theory and the impact to the measurement results of non-ideal factors which effect the measurement accuracy, were analyzed in this thesis. On this basis, a variety of designs were designed to eliminate the effects on the results of measurement which caused by non-ideal factors to improve measurement accuracy. The signal strength detection circuit was proposed to solve the problem in general time difference flowmeter that the transducers can not be completely aligned during the assembly process lead to weak signal strength; the weak signal strength results in decreased of accuracy or even the flow can not be measured. The design ideas of circuit symmetry and electronic channels exchange were used to eliminate the circuit delay and time measurement errors caused by temperature. A way of resetting the system time difference was designed to offset the time difference lead by the differences of the transducer performance, by which the restrictions that transducers must be fixed in previous measurement system were broken out, and it was able to adapt to various measurements environmental to improve the system's measurement accuracy.The ACAM Company's next-generation high-precision measurement of chip TDC-GP2 and TI Company's low-power microcontroller MSP430F1611, matching with the CF cards, FAT32 file system of data storage and CF-Reader circuit were used in this system, all of which formed a flow measurement system that can work independent from the computer and store data collected in CF card. Bus-switch circuit was designed to enable a computer access the CF Card directly, so the results of the measurement can be read and processed in the form of a document. Finally, the accuracy and measurement stability of the system were achieved in the pool of walking-car validation tests.