Ultraschallbasierte Geschwindigkeitsmessung nach dem Sing-around-Verfahren

In this thesis, a measuring system for very low flow velocities in the range of 50 µm/s for leakage detection in household water mains was set up and examined. For this purpose, the ultrasonic time-of-flight principle is exploited. This method is based on different propagation velocities caused by the flow and thus different propagation times of the ultrasonic waves with and against the flow direction. This method requires a very high time resolution for measuring low flow velocities, since the propagation times differ only minimally for the opposing directions. A method to reduce the resolution requirement of the time measurement or to increase the accuracy of the measurement of the flow velocity for a given temporal resolution is the so-called sing-around technique. In this method, the length of the propagation path is virtually lengthened by sending a new ultrasonic pulse in the same direction immediately after receiving one at the end of the propagation path. This is done N times for both directions, which increases the propagation time difference by this factor. The unknown flow velocity is calculated from the time difference. In this work, the implemented sing-around-system was built up. For this purpose, a suitable measuring section and an electronic circuit were designed and built-up. Furthermore, the entire system and its components were characterized. In the course of the work it turned out that the given component, which is used for the excitation of the system, limits the resolution of the time measurement to approximately 25 ns, because of it’s clock. A flow velocity measurement with the desired accuracy is therefore not possible.