Principles and practice of electrical engineering (1914)
Gray, Alexander, 1882-1921 · New York [etc.] McGraw-Hill Book Company, inc. · leaf 224
199 In order that a moving coil instrument may be used for themeasurement of alternating currents, the magnetic field and thecurrent in the moving coil must alternate together. This resultis obtained by replacing the permanent magnet by an electro-magnet as shown in Fig. 218. The current to be…
Electrical engineering
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