An improved frequency meter for commercial power frequencies

While frequency meters of prior type admirably serve the purpose for which they are intended, their construction has been such as to necessitate the use of an external reactor. This external reactor is in most cases not objectionable, but for certain applications, where space is at a premium, a self-contained instrument is preferable. This paper describes a frequency meter in which the external reactor has been eliminated by using an iron-core cross-coil instrument, the iron core serving the purpose of the normally external inductance, at the same time shortening the high reluctance air gap necessary for the moving coils.