Messgerät zur Ultraschall-Strömungsmessung in Gasen und Flüssigkeiten

Trains passing tunnels cause pressure-waves. This can adversely affect the tunnel drainage. Under certain circumstances, the direction of flow could be reversed. For the purpose of investigation a measurement system is needed, which is able to simultaneously measure speed as well as direction for both air and water. The measurement system should be suitable for measuring small velocities of several cm/s with high precision, while having a range of several m/s. A sensor based on the ultrasonic time-of-flight principle was chosen. For this sensor the method of ultrasonic transit-time difference was selected. The required high precision of the time measurement was achieved by a time-to-digital converter with a statistical uncertainty of 55 ps. To complete the measurement system a sensor for fill level as well as sensors for humidity, temperature, and pressure of air were added. The electronics and the battery were mounted inside a water-resistant box. Since the generation of a constant and laminar flow for the calibration of the measurement system is very difficult due to different hydro-mechanical effects a measurement setup was chosen where the sensors are moved through a stationary medium. Thus, a nearly constant flow can be generated. A vibrometer served as reference. The performed measurements achieved an uncertainty of 0.1 cm/s. Additionally, the suitability of the system for the measurement of higher flow velocities in the range of m/s was confirmed qualitatively.