Patent GB-191200528-A (GB)
Title: Circuit Arrangements for Connecting a Trunk Line Telephone Exchange with the Subscribers of a Local Automatic Exchange.
Filed: 1912-01-06
Granted: 1912-05-30
Abstract: 528. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Jan. 6. Automatic and semiautomatic e x c h a n g e - systems; metering systems. -In automatic exchangesystems, such as that described in Specification 19,185/11, in which a conversation is registered when the called subscriber answers, means are provided for putting different test-potentials on a subscriber's test - terminals according to whether he is disengaged, or engaged as a calling subscriber, or engaged as a called subscriber, or engaged in a t r u n k connexion. An operator at a trunking exchange, in extending a trunk call to a subscriber at the automatic exchange, receives a distinctive signal in accordance with the test-potential on his terminals. If the signal shows that he is engaged as a calling subscriber, she at once completes the trunk connexion to him, thereby releasing the existing " local " connexion. But if the signal shows that he is engaged as a called subscriber, she first asks the number of the calling subscriber to learn to whose account an allowance must be entered for the interrupted call. When the trunk call has been completed, the subscriber's test-terminals are marked with a fourth distinctive potential, and a trunk exchange operator attempting to extend a second trunk call to the same subscriber would receive a signal warning her not to interfere. The switching system for interconnecting subscribers at the automatic exchange is substantially the same as in Specification 19,185/11, and includes preliminary selectors such as VW1, first selectors, and connectors LW. The trunking exchange operator has special selectors and connectors FGW, FLW for obtaining access to any subscriber such as T1. The connector FLW comprises testrelays P1, P2, P3 of different sensitiveness, which are connected, in the third position of the side switch, to the wanted subscriber's test wire c, and control the connexion of signalling-devices FV, OVg, OVr, and Fr. If subscriber T, is disengaged, current flows through relays P3, P2, P1, over test wire c, normal contact e, windings t2, t1 of cut-off relay Tr, and normal contact k, to earth. All the relays are energized, and relay P1 short-circuits resistance p1, to mark subscriber T1 busy, and connects the signal Fr to the trunk line. The operator then moves the side switch on into speaking position. If, as indicated in Fig. 2, subscriber T, is engaged as called subscriber in a local call, current passes through the circuit already traced, but relays P3, P2, P1 are now shunted by the connector test-relay P, so that only relay P3 responds and signal OVg is connected to the trunk line. The operator now moves the side-switch of the connector FLW to fourth position and enquires the number of the calling subscriber, and then moves the side switch to fifth position, completing the trunk connexion to subscriber T1 and shortcircuiting relay P, which effects the release of the previcusly-existing connexion. If subscriber T1 is engaged as calling subscriber in a local call, his test lead is earthed over a resistance in the first selector, and the relays P3, P2, P1 receive current in parallel with the metering-magnet Z1 and winding t2 of relay Tr, which are connected over contacts t and 3 and off-normal contact k1. Under these conditions, relays P3, P2 are energized and signal OVr is connected to the trunk line. The operator completes the connexion as before. If subscriber T1 had been engaged already in a trunk conversation, there would have been full-battery potential on his test-lead c from a side-switch contact of a trunk-line connector similar to FLW. The relays P3, P2, Pi under these conditions would receive no current, and the signal FV would be connected to the trunk line.