Acoustic/ultrasonic testing is now a common method in the field of nondestructive testing for detecting material defects or monitoring ongoing mechanical changes in a structure during operation. In many applications, piezoelectric transducers are used to generate mechanical waves inside the specimen. Their actual operating frequency is highly dependent on the dimensions of the transducer. Larger dimensions of the piezoelectric transducer allow for a lower operating frequency. However, these dimensions limit the use of piezoelectric transducers in certain applications where the size of the transducer is restricted due to limited installation space and when low-frequency excitation is required. One application that places these requirements on the transducer is the monitoring of mechanical seals. Here, the transducer must be mounted on the stationary ring of the seal. In this paper, a continuously operated electromagnetic acoustic transducer (EMAT) is presented as an alternative to piezoelectric transducers as a transmitter. The advantage of a EMAT is that it meets the requirements of limited sensor size (sensor area < 10 × 6 mm) and can excite mechanical waves with frequencies below 10 kHz. A structural analysis of the stationary ring shows that the first two mechanical resonances occur around 4 and 5.5 kHz. An experimental study meterologically demonstrates the ability of the EMAT to excite these first two mechanical resonances of the ring. A comparative simulation agrees well with the measurement.
ZusammenfassungWinde und Luftströmungen stellen eine potentielle Bedrohung für Hochspannungsleitungen dar. Die Luftbewegungen lassen die Leiterseile in beliebige Richtungen schwingen und verursachen mechanischen Stress an den Aufhängepunkten und den Leiterseilen. Um die Amplitude der Seilauslenkung zu messen, kann ein Vibrationssensor, basierend auf einer Beschleunigungsmessung, an der Leitung angebracht werden. Damit der Sensor in einem solchen Umfeld korrekt arbeitet und die Auswertung der Seilauslenkung ordnungsgemäß erfolgt, müssen zuerst Überlegungen angestellt werden. In diesem Beitrag sind diese herausgestrichen und in einen Laborprototypen eingeflossen, welcher anhand von Laborexperimenten verifiziert und charakterisiert wurde. Die Leistungsaufnahme des Prototyps sowie dessen Messunsicherheit und der mittlere quadratische Fehler, bezogen auf die Auslenkung, werden präsentiert.
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