Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems (1921)
Smith, Arthur Bessey, b. 1875, Campbell, Wilson Lee · New York : McGraw-Hill · leaf 297
s the busy test in the usual way and if the line is free inserts the plugin the jack. This closes the sleeve circuit through cut-off relay /?-48,sleeve of jack and plug, and lamp L-9 and winding of relay R-45 in par-allel. The lamp lights as a guard for ringing purposes. Relay RA5 cutsoff the lamp… … Fig. 238.—Wipers and magnets of switch unit. B operator that conversation has begun. The two lamps L-9 and L-10are the individual supervisory signals for the two subscribers. When the called subscriber hangs up, relay RA6 will fall back andlight the lamp L-9. When the calling subscriber hangs up it…
Telephone
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