The practical telephone handbook and guide to the telephonic exchange (1906) (14733156326)

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:

ads, it is the practice to usesome form of self-restoring annunciator, such as the eyeball,Fig. 164, which is fixed in a vertical position, or the visualsignal, Fig. 166a, which is fixed in a horizontal position,such as on the cord shelf, where it can be directly associatedwith the cords. These annunciators show while the currentis on the line and are visible while talking is going on, anddisappear when the current ceases,—viz. when the receiversare hung up—so that the signal for clearing is a negative one,the disc disappearing when this is to be done. 188 PRACTICAL TELEPHONE HANDBOOK Cord Circuit.—Fig. 215 shows the connecting cord andoperators connections, and it will be seen that when twosub-exchange lines are connected together by the two plugs,the speaking current is supplied from the bus bars, throughtwo contacts of a cut-off relay, C.O.R., and a double-woundretardation coil, R.C. Two independent clearing visualsignals are inserted in the tip conductor of the cords,* these

Text Appearing After Image:

Cord Cmcuir Fig. 215 annunciators being shunted by non-inductive resistances, R.R., so as not to interfere with the speaking. J unction-Line Connections.—Fig. 216 shows the connections of a junction line joining the sub-exchange to the main exchange, and it will be seen that each junction is furnished with two jacks at the sub-exchange, one of which (a 7-point) is used in the day-time, when an operator is in constant attendance, and the other (a 5-point) at night, when it is required to leave one of the sub-exchange lines plugged through to the main exchange. When the day jack is used a 600-ohm retardation coil becomes connected as a shunt across the line; the purpose of this is to complete the circuit for the supervisory signals at the main, so that the operator there will not be troubled by her supervisory lamp remaining lit un- * In the latest practice these signals are inserted in the ringconductor. EXCHANGE SWITCH-BOARDS 189 til the called-for sub-exchange subscriber answers, t

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1906

Northeastern University, Snell Library

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public domain