Identifier: americantelepho00mill (find matches)
Title: American telephone practice
Year: 1905 (1900s)
Authors: Miller, Kempster B. (from old catalog)
Subjects:
Publisher:
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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relay must be so adjusted as to work properlythrough the resistance of the line and the talking apparatus, but itmust be made so insensitive as not to work through the resistance ofthe line and that of the bells. Such conditions are to be avoided, ifpossible. A modification which is being used to a considerable extent by theBell companies, and which effectually removes the difficulty due tothe marginal adjustment of the line and supervisory relays, has beendevised by Messrs. Thompson and Robes. In this system each stationis provided with a relay especially designed for use with alternatingcurrents, each relay being bridged across the metallic circuit of theline in series with a two-microfarad condenser. This arrangementis shown in Fig. 327, which shows two four-party lines connectedby the usual Bell multiple switch-board circuits at the central office.The contacts of each of the relays at the subscribers stations are soarranged that when the relay is operated it will connect the usual
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FIG. 327.—THOMPSON & ROBES PARTY-LINE SYSTEM. 440 PARTY LINE SYSTEMS. 441 biased bell to earth from one leg or the other of the metallic line,such connection being made only during the process of ringing.The ground branches are detached from the line at all times, exceptduring the ringing operation, but are made available for use inringing by the action of ringing when pulsating current is thrownon the line. When the proper (say, negative) pulsating current is appliedbetween the sleeve side of the line and ground, current will flow outto the sleeve side of the line through the condensers at all of thestations in multiple, and back to the ground on the tip side of theline at the ringing key. All of the relays at the subscribers stationswill be thus operated, which will establish new ground connectionsat the subscribers stations. The negative current then in passingthrough the bell at station No. I to ground will ring that bell, whilethe bell at station No. 2 will not be rung, bec

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