Patent GB-402193-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1932-08-03
Abstract: 402,193. Automatic exchange systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and DRYSDALE, L. H., Ericsson Telephone Works, Beeston, Notting- ham. Aug. 3, 1932, No. 21756. [Class 40 (iv).] The conductor over which potential is applied from an individual circuit to a common control circuit for starting or seizing purposes, includes a rectifier so that subsequent application of an opposite potential from the individual circuit does not disable the common circuit so far as other individual circuits are concerned. The invention is described in connection with the start wire of a group of finder-connector links and enables the use of line circuits having a single relay of ordinary type. This relay marks and starts at the same contact and remains connected to the line during a connection to serve as a battery feed. The connectors are single motion switches with single lines corresponding to digits 1-9 and 01 to 09 and a group of lines at the end of the banks reached by dialling 00. The group may however occur in an intermediate position. Operation of call finder. A call from subscriber S operates the line relay A which connects ground over metal rectifier RC to operate AS in the control circuit if disengaged. BB pulls up in series with BC(ii) which holds over (i). If the assignor is standing on an idle link, AD operates over wiper cw6 (normal) of the connector in series with FDM which operates in a self-interrupting circuit when AD shorts its winding (i), the circuit of assignor magnet being opened by AD. If the link is busy, ground over connector wiper cw5 from any idle link operates ADM and the assignor steps until AD operates. When the calling line is found, DR pulls up to battery over resistance R1, locks and stops the finder. The resistance of DR may be low enough to permit the ground over its winding to short circuit the start relay AS. Relay B now pulls up and opens the circuit of AS, operates switching relay F which holds to ground at a2 in the line circuit and extends this ground to MS which starts the ringing and tone equipment (not shown). AD also falls back. AS opens the series circuit for BB,BC but the weighted vibrating armature of BB keeps BC(i) operated for a predetermined time, say 8 seconds, BB being normally re-operated before the expiring of this period. Dialling tone passes from connector wiper cw7 to the calling line. Connector. Relay A repeats dialled impulses at a3 to magnet CDM and relays C and F(ii) in parallel, relay F thus holding during breaks which open the circuit of F(i). Relay C holding during the train, re-makes the series circuit described above for BB, BC, and holds B independently of DR which falls back on the first relapse of A followed by Z slowly. On the first step of the connector, wiper cw6 connects ground over the bridged arcs to the private wire of the calling party. On the relapse of C at the end of the train, BC again becomes dependent on the vibrating armature of BB, and H(ii) tests the wanted line during the period of B the circuit of which is now open. If the line is free, H pulls up, locks over H(i), short-circuits H(ii), and releases switching relay F for the time being by a short circuit over h2 to complete the ringing circuit. Relay MS is held to maintain the ringing &c. apparatus but B falls back, re-operation of the start relay AS being prevented by ground on the private wire. Ringing current now passes from terminal AC over a contact of interrupter controlled relay TR to ground over a winding of the line relay (A) of the wanted line, tone being passed back over condensar Q1 to the calling party. When the called party replies, his line relay grounds wiper cw4 to re-operate relay F and trip the ringing in a circuit which includes contacts tr2 of the interrupter relay which prevents the premature operation of F due to the intermittent operation of the line relay during the ringing periods. The speaking circuit is now complete, battery being fed to each party over his line relay. MS falls back. If the wanted number has two digits (first digit O) relay B holds over wiper cw8 at the end of the first train dependent on BC so that if the next train is dialled before the vibrating armature of BB dies down, the connector will be again stepped on. Release of control circuit. On the relapse of B, a circuit is completed for assignor magnet ADM and relays X and Y operated originally by AS, fall back slowly, the circuit of ADM being ultimately opened by X to step the assignor. Ringing connections for the various link circuits. It will be seen that the ringing arrangements although shown in the common circuit are independent thereof, and as more than one wanted sub-station at a time may be taking ringing current due to delay in answering, arrangements are provided for equalizing the load on the generator. As shown, four link circuits are provided for, the ringing periods for two over break contacts tr1, tr3 corresponding with the silent periods of the other two which are rung over make contacts tr5, tr7. The corresponding contacts tr2-tr8 in the circuit controlling relay F are similarly arranged so that they are closed only during silent periods. Release of speaking connection. When the calling party hangs up, A, F and H fall back and the connector homes over cw5, the finder remaining off-normal. Busy signal. Relay H does not operate and when B relapses to free the control circuit, busy tone is sent back over wiper cw7 of the connector. Although busy tone is connected up immediately the connector steps off normal it will not be heard during impulsing owing to the usual disabling of the receiver. Busy tone is not connected to the 10th contact. Group hunting. As shown, the last five lines of the connector banks form a group, and by dialling OO the first line of the group is tested by H as before. If this line is engaged, HS pulls up and locks and when B relapses, C re-operates and magnet CDM is energized, X being maintained by C which re-operates B to open circuit the magnet and step the connector. This interaction between B and C continues until the connector finds an idle line or reaches its last contacts, HS being held operated over cw8 unless H pulls up on an idle line and releases HS. If the connector proceeds to the last contacts HS falls back, H pulls up if the line is free and busy tone connected to the last terminal in cw7 is sent back if the line is engaged. The group may be arranged so that it is reached by dialling say 04 if the connections of bank cwS to HS and of cw7 to busy tone are suitably made. Faulty apparatus. Normally, AS on seizure of the control circuit operates Y which is followed by slow operating relays Z and X. If the finder does not step, DR and B fail to operate, Y falls back followed by Z and X slowly. A circuit x3, z1 as6, 15 for magnet ADM is thus made and broken and the assignor steps on to the next link which, if busy, releases AD to complete the self-driving circuit of the assignor. X re-completes the circuit of Y which re-operates Z. If AD does not operate to an idle link, the assignor hunts continuously, and ground from conductor 15 is connected to hold X, light lamp L1 and operate an alarm relav AL. Standstill releases. If dialling is delayed beyond the time BC is held by the vibrating armature of BB, the relapse of BC operates PG which has a contact individual to each link. PG lights lamp L2. The relapse of BC also energizes C and energizes the connector magnet CDM (F being operated at this time). Relay B falls back slowly, energizes assignor magnet ADM and releases CDM to step the connector which grounds the calling private wire as previously described. This ground shunts out DR which is normally released by dialling, and Z falls back, PG being held by ground over connector wiper cw5. Busy tone is sent back over wiper cw7. Relays C, Y, X relapse slowly and the circuit of magnet ADM is opened to step the assignor. The link circuit remains held so long as the calling party is on the line, ground from cw6 on the private wire marking it busy, and shunting out the start relay. If the subscriber hangs up, PG falls back and extinguishes the alarm, but if he does not or if there is a permanent loop, the alarm is maintained until relay PG is released at key K. Similar operations ensue if delay occurs after the first digit has been dialled but in this case DR,Z will have been released previously.