Patent GB-259694-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/00
Filed: 1925-07-27
Abstract: 259,694. Western Electric Co., Ltd., (Deakin, G., and Polinkowsky, L.). July 27, 1925. Automatic exchange systems.-A common conference circuit which may be associated with a calling line is provided with selecting means whereby the other parties may be connected to the circuit under control of the calling party. In the system described the calling party dials a particular conference number to a local connector of the kind described in Specification 197,797. This starts the finder of the appropriate conference connecting circuit, and when the calling party is found the local circuit is released. The calling party then dials the first number and the wanted party on removing his receiver is connected to the conference circuit LCT by his relay 8 which locks up over the loop and provides him with talking battery. The calling party may then hang up his receiver to release the conference circuit and again dial the conference number to a local circuit to get possession of it again. Alternatively he may dial the conference number without hanging up. This has the effect of restoring the conference connector and on receiving dialling tone he dials the number of the next party and so on. Selecting first party. The local connecting circuit, in response to the conference number, grounds LC and marks the calling d-terminal. If the conference circuit is not in use by any other person its sequence switch is in position 1, relays 1, 2, 4 pull up and magnet SM drives the finder LF. When the line is found, relay 3 stops the finder and energizes switching relay 5 which grounds the c-terminal to release the local connecting circuit and energizes relay 7 which co-operates with the back-stroke magnet SSM to drive the sequence switch to 1¢ and then to 2. Relays 1, 2, 3 fall back but relay 4 remains energized by impulse relay 6 and relay 5 is locked up in series with relay 20. In position 2, relay 9 pulls up over the tone starting wire DTR and sends back dialling tone from DT. The tens digit is repeated to the magnet SM1 of the switch FS1 over relay 11 which energizes relay 7. At the end of the digit relays 11, 7 fall back and the sequence switch moves to 2¢ and then automatically to 3¢. In 2¢ and 3 circuits are made for energizing relays 10, 12, 13 in various combinations in accordance with the position to which FS1 has been set. Relay 10 determines which switch and relay 12 which set of wipers shall be used for completing the connection, while relay 13 determines whether the selected switch shall be stepped by the units digit from N or from N1. In 3¢ a self-interrupting circuit is made for the selected stepping magnet. The switch is stopped at N or N1 by the energization of relay 14 which also causes the sequence switch to move to 4. When the switch FS2 is to start from N, relay 14 is energized as soon as 3¢ is reached. In 4 the units digit is received after which the relapse of relay 11 causes the sequence switch to move to 4¢ and then automatically to 6. Busy test and signal. Subscribers who can be brought into a conference have relays 15, 17, 8 in addition to the line and cut-off relays 18, 16. If the wanted party is busy in an ordinary call, his relay 15 is energized in parallel with the cutoff relay and grounds his test terminal in the conference connector. Relay 13 is re-energized momentarily in 4¢ over its right hand winding, and connects its left hand winding to the test wiper, and if the line is busy, holds over this winding in 5 and is locked over D, C and the other winding in subsequent positions. In 6 relay 9 pulls up and sends back a signal as in the case of dialling tone. Ringing current. If the line is idle, relay 13 fails to hold up in 5¢ and connects ground Cover R to the test-wiper to energize relay 17 but not relay 8. Relay 17 energizes the cut-off relay 16. Relay 14 pulls up in 6 and the sequence switch moves to 7 in which the ringing generator is started over RC and ringing current is sent out over RC<1>, H, the loop, G, 14. When the called party replies, relay 14 causes the sequence switch to move to 7¢ from which it goes automatically to 9. In 7¢ R is short-circuited and relay 8 connects the called party to the circuit LCT, holds relay 17 and locks itself over the loop to provide talking battery. In 9 the calling party is in talking relation with the circuit LCT. Selecting remaining parties. If the calling partly hangs up, the relapse of relays 4, 5 causes the sequence switch to move to 10 in which FS2 is restored to normal and then to 11 in which FS1 is restored and finally to 1. The subscriber again dials the conference number to a local connecting circuit and then operates the con- 28 ference circuit as previously described. Alternatively the subscriber may dial the conference number without hanging up. This energizes relay 19 which locks up and produces the same effect in starting the restoration of the sequence switch as the relapse of relay 5. Beyond 10 relay 19 is unlocked and the restoration is effected over the lower left-hand contact of cam H so that the switch moves straight into 2 to send dialling tone. Leaving and re-entering conference. If the initiating party releases the conference connector when all the parties have been associated, he can come in again by dialling a spare number the talking terminals of which are bridged to cause the sequence switch to move through the ringing position. The other parties can leave the conference by hanging up their receivers and cannot be brought in again without the use of the conference connector.