The practical telephone handbook and guide to the telephonic exchange (1906) (14569701847)

Identifier: practicaltelepho00pool (find matches)

Title: The practical telephone handbook and guide to the telephonic exchange

Year: 1906 (1900s)

Authors: Poole, Joseph

Subjects: Telephone

Publisher: New York, Macmillan Co.

Contributing Library: Northeastern University, Snell Library

Digitizing Sponsor: Boston Library Consortium Member Libraries

Text Appearing Before Image:

158.—Full size lever are similar to those of the 2-coil drop, so that Fig. 157serves as elevation of both kinds. As the magnetic circuitis of very small reluctance the drop is very sensitive, and hasgreat impedance, for which reason it must always be insertedas a shunt to a speaking circuit, and never directly in thecircuit. This indicator offers great impedance to the rapidlyalternating speaking currents, but only its normal ohmic re-sistance to the comparatively slowly alternating ringing

Text Appearing After Image:

Fig. 159.—Scale % currents. Another purpose which the iron jacket serves isto confine the magnetic hues of force to the inside of the coil, SWITCH-BOARD APPARATUS 147 and so prevent inductive effects on adjacent coils. The coilconnections are brought to the outside by straight, stiff wires,which pass clearly through larger holes in the armature. Ericsson Drof.—Figs. 159 and 160. This is a single-coildrop, which differs somewhat in principle from those described.It is one of the many forms of indicatorand relay worked on the knife-edgeprinciple which have lately come into use.One end of the core is made into a wedgeor knife-edge form, 6, on which is pivotedthe armature. The armature passes rightto the other end of the coil, and when acurrent passes the end c is attracted tothe soft-iron pole-piece d, and the shutter eis released by the catch moving downward. In this manneithe air space at one end is dispensed with, and the magneticreluctance is lessened. A screw and spiral spring a

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1906

Northeastern University, Snell Library

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public domain