Patent GB-289880-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1928-04-27
Abstract: 289,880. Associated Telephone & Telegraph Co., (Assignees of Crocker. T. F.). May 6. 1927, [Convention date]. Automatic and semi-automatic exchange systems.-In a private branch exchange, the operator associates the junction with the selecting switches and associates her circuits with a calling junction or with the leads such as 301 - - 303 over which she is called when a privileged subscriber does not want to set up an outgoing call himself, by means of relays which are energized by the momentary operating of keys and lock up. The locking circuits of the relays that connect up the operator's circuits, and the circuits of the junction busy lamps, include off-normal contacts on the operator's switch hook. A single dialling key is provided which according to its position enables the operator to dial to the local selector or over the jurction. The wire 6 over which a connector discriminates between privileged and non-privileged calling subscribers, is grounded by the release relay to give a lamp signal L<3> to the P.B.X. operator when she takes the connector into use for setting up a connection between one of the two way junctions and a local subscriber. Incoming call. Relay 207 pulls up, to busy the junction, in series with the distant ring-trip relay (which remains unoperated). Relay 209 in response to the ringing current enezgizes 208 which locks up, connects up a further busy ground, and lights the calling lamp L' in series with 314 which, if the operator has thrown K<3> to the right, operates a buzzer. The operator throws the key K of the calling junction momentarily to the left to energize 204 which locks up in series with 313 and energizes 206. Relay 313 prevents the operator from associating herself with another junction or with a calling local subscriber. Operation of 204, 206 cuts a resistance R<1> into the circuit of the calling lamp which goes out, bridges the operator's set across the wires 252, 254 to start the incoming line switch hunting for a connector, and puts a bridge 312, 201 across the junction to trip the ring. Relay 201 pulls up in series with the back-bridge relay and energizes 202 which puts another busy mark on the junction, cuts off 207, lights the busy lamp L<2> and energizes 203 over the lower junction wire. Relay 203 locks up, disconnecting itself from the junction and completing the lower talking wire. The operator is now in communication with the calling party, and when the connector is ready, as indicated by the glowing of L<3>, throws K<2> to the right to prevent the calling party from hearing clicks, and dials the wanted number. When she hears the ring-back signal, she replaces her receiver to release 204, 313. The local switches are then held by the lower winding of 206 and the junction is bridged by 201, 207. The local back-bridge relay 14 on operating puts out L<3> and releases 208. When the called party hangs up, L<3> re-lights and, since 208 is back and short-circuits R<2>, L<1> also, and 314 gives a buzzer signal if K<3> is operated. The operator then throws K momentarily to the right whereupon 205 removes the holding bridges. Outgoing call established by subscriber. Shaft springs 92 operate on the 10th level and energize relay 15 in series with ring-trip relay 16 which locks up. Relay 15 replaces the local battery connections to the back-bridge relay 14 by a bridge. Shaft springs 91, energize busy relay 17 which now acts as the stepping relay, When 19 switches through, a circuit is made from 221 over 14, 201 and the upper junction wire, for the incoming line relay and the switch LS<3> hunts for a group selector. 201 energizes 202 and prepares the busy lamp for operation when the operator lifts her receiver. 203 pulls up over the lower junction wire and the line relay in the group selector and connects the lower wire back to the connector. Subsequent digits are repeated over the junction, the rotary dialling relay 18 substituting a direct bridge for relay 14. Outgoing call established by operator. On the 9th lovel, the connector hunts for leads such as 301 - - 303, and switching relay 19 operates in series with a call lamp L<4> and relay 314. The operator throws the appropriate key K<1> whereupon 300 connects her to the calling party, extinguishes L<4> and locks up when she removes her telephone in series with the isolating relay 313. The calling party then gives the wanted number and hangs up and the operator releases 313, 314 with her hook-switch and seizes a junction by throwing its key K to the left whereupon its relay 204 energizes 206 and locks itself in series with 313. She then puts her telephone set across the junction by throwing K<2> to the left and starts the distant line switch by means of a circuit 221, 327, 325, 201 and the upper junction wire. Relays 201 - - 203 pull up as when the subscriber sets up a call. Having dialled the number, she calls the local calling party and supervises the call as in an incoming call. Restricted service. Non-privileged subscribers have no ground connection 9. and if they set a connection to level 9 or 10, 17 pulls up over resistance R<5> and locks itself, and busy tone is connected up on the relapse of the series relay, the rotary magnet being unable to pull up over R<5>.