The use of vibration instruments on electrical machinery

W. B. Creagmile: Mr. Ormondroyd has mentioned a vibrating-reed type of instrument with one reed. The common use of vibrating-reed instruments having a series of tuned reeds along a marked scale, to measure revolutions per minute and a-c. frequency, is not mentioned in the paper. The reeds of the tachometer pick up mechanical vibration from the machine to which the instrument is attached. In the frequency meter, the reeds are set in vibration by alternating current flowing through an electromagnet placed in series with resistance across the mains.