File:Resonant reed frequency meter.jpg

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Summary

DescriptionResonant reed frequency meter.jpg	English: A resonant-reed frequency meter from 1921. The reed frequency meter, an obsolete technology, was used to measure the frequency of alternating currents below 1000 Hz. It was used to check the frequency of alternators supplying local power grids and the higher frequency AC used for traction motors on streetcars and ships. It consists of a small electromagnet placed next to a steel strip cut into reeds of graduated lengths. When the alternating current to be measured is applied to the electromagnet it vibrates the strip. The reed which is resonant at the applied frequency will absorb energy and vibrate with large amplitudes while the other reeds will hardly vibrate at all. The ends of the reeds project through the face of the instrument next to a graduated frequency scale. Alterations to image: enlarged image of internal parts so it was the same size as face, and moved it to right of face.
Date	1921
Source	Retrieved from Eugen Nesper 1921 Handbuch der drahtlosen Telegraphie und Telephonie: ein Lehr- und Nachschlagebuch der drahtlosen Nachrichtenübermittlung, Vol. 1, Julius Springer, Berlin, p. 107, fig. 82 and 83 on Google Books
Author	Eugen Nesper

Licensing

Public domain	This media file is in the public domain in the United States. This applies to U.S. works where the copyright has expired, often because its first publication occurred prior to January 1, 1929, and if not then due to lack of notice or renewal. See this page for further explanation.	United States
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