. American telephone practice . bridge is formed by themacross the now completed circuit. The condition with respect to the talking circuit is now that shownin the lower schematic diagram of Fig. 513, and it only remains toaccomplish the ringing of the called subscribers bell. To do thisthe calling subscriber presses his ringing button which, as beforestated, grounds the vertical side of the line at his sub-station, andthus energizes the vertical relay, V2 R, at the connector in the usualmanner. When the connector side switch moved into its thirdposition, the coil of the ringing relay was brou
. American telephone practice . bridge is formed by themacross the now completed circuit. The condition with respect to the talking circuit is now that shownin the lower schematic diagram of Fig. 513, and it only remains toaccomplish the ringing of the called subscribers bell. To do thisthe calling subscriber presses his ringing button which, as beforestated, grounds the vertical side of the line at his sub-station, andthus energizes the vertical relay, V2 R, at the connector in the usualmanner. When the connector side switch moved into its thirdposition, the coil of the ringing relay was brought into the localcircuit of the vertical relay of the connector. Pressing the ringingbutton at the calling sub-station at this time therefore causes theenergization of the ringing relay. These circuits are most clearlyshown in Fig. 517. The action of the ringing relay is exactly the same as that oi anordinary ringing key in a manual switch-board. It cuts off theline behind it and establishes connection between the limbs of the. 720 AUTOMATIC SWITCH-BOARD SYSTEMS. 721 called subscribers line and the calling generator, G. The bell ofthe called subscriber is thus rung, and when he responds the con-versation ensues over the circuit shown in the lower diagram of Fig. 513. No mention has yet been made of the back signal relay, B S R,and the back release relay, B R R. The action of the back releaserelay may be best understood when the question of releasing theline is discussed later on. It may be said, however, concerning theback signal relay, that its function is to enable a subscriber whohas been called by a toll operator to signal this operator if desiredby means of his ringing button. If the called line had been busy at the moment when the connectorwipers moved upon its bank contacts in seeking to connect with it,then its private normal would have been grounded. A line maybe busy from two causes: either because it may have been sought outand connected with by another line, or it
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