Patent GB-598893-A (GB)
Title: Telephone exchange systems
IPC: H04M3/54
Filed: 1944-04-28
Abstract: 598,893. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. April 28, 1944, No. 7991. Convention date, June 7, 1943. [Class 40 (iv)] [Also in Group XXXVIII] In an automatic exchange system, affording a variety of special services, a special service selection circuit reached over the normal train of automatic switches may be operated to select and associate a required special service with the calling line, whereupon a tone signal is reverted to the subscriber until he hangs up and releases the switch train. The system enables messages to be recorded at the exchange either by an attendant or by automatic means, and later repeated to the subscriber, and may be used to provide super-audio programme services, private connections with a toll board, telegraph or stock ticker offices, or night service of a PBX. Programme and news service and private connections to telegraph or stock ticker offices. The desired service is selected by a special 3rd selector reached over the zero levels of the 1st and 2nd selectors. When the 3rd selector stops and the wipers make contact with their terminals, a relay SCR individual to the selected service pulls up and energizes a relay STR common to all the services to prevent any other special 3rd selector from stopping. SCR also makes a circuit for another common relay SBR which is only completed when the identification circuit (described in Specification 592,846) is not in use by the wire-chief or the distant toll operator. On operating, SBR excludes these from control of the identification equipment, disables all the first identification finders, operates the identification relay 1R in the 1st line finder circuit and puts ground on the special service relays such as SSR1 corresponding to the selected service in all the line circuits. The relay SSR1 of the calling line operates via the marking circuit connected up by the IR relay and locks up. SBR also operates ER in the special 3rd selector which switches through to a busy tone and frees the special service selecting circuit and identification equipment by releasing SCR which falls sluggishly to give time for the operation of SSR1. The subscriber now hangs up and the switch train is released in the usual way, but SSR1 remains locked up until the differential relay DR is operated over a key at the substation. Personal service for giving or taking messages for absent subscribers. The subscriber operates in the manner previously described a relay 3SSR, Fig. 3, which connects the incoming line to relays 3AR, 3BR and the a, and b wires leading to the normal line circuit via front contacts of a relay 3GR, which is energized by the cut-off relay, to the attendant's line circuit. The removal of the loop through the substation set releases the switch train, whereupon 3GR falls and allows 3AR, 3BR to pull up over the subscriber's loop. 3BR is shunted out immediately, but before it falls applies a burst of ringing current to the attendant's line, whereupon 3LP lights the calling lamp. The subscriber can now communicate his wishes. When he hangs up, 3SSR remains operated and in consequence incoming calls are extended via contacts of 3GR (energized by the cut-off relay) to the attendant. If the subscriber wishes to call the attendant, he simply removes his receiver and 3AR, 3BR operate as before and cause a calling signal to be given. If at this time an incoming call arrives, the ringing current can be heard faintly via small condensers and the subscriber can drop the special circuit if he wishes by energizing 3DR with his key GK. When the attendant plugs into the line while the subscriber is absent, 3FR pulls up and prevents the operation of 3ER which is energized subsequently by the ringing key to apply ringing current to the line. When the subscriber replies, 3AR pulls up, but not 3BR, which is shunted out by 3FR. Automatic service for recording and reproducing messages. Before leaving his substation, the subscriber causes the operation of 4SSR1, Fig. 4, in the manner previously described. This connects his loop to relays 4CR, 4DR, of which the former pulls up and sends back a busy tone if the wire of the recording equipment is fully re-wound, there being a normal re-winding circuit whenever the equipment is out of use. At the same time, the a and b wires to the normal line circuit are connected to the A and B terminals of finders for associating the circuit shown in Fig. 4 with common equipment shown in Fig. 5. Assuming the wire to be fully re-wound, 4FR is operated and when a call arrives, a common start relay 4CSR is operated and the finders of the common equipments hunt under control of their relays T1R, T2R, the operation of which in the successful finder shunts down 4CSR. The ringing current then operates CLR which locks and connects CJR to an interrupter. When the latter makes, CJR locks, connects the incoming circuit to a gramophone, thus operating the ring trip relay, and connects the interrupter to CKR. The gramophone informs the calling party of the position and after an interval CKR unlocks CLR, CJR and couples the line through an amplifier to the recording and reproducing magnet RT, and energizes the wipe-out magnet W and the forward drive clutch magnet Cl2 of the recording set. The driving circuit is cut by relay CTR operated by a time switch TA, which is re-set by a voicecurrent operated relay VOR, if a pause of more than 10 seconds occurs in the message being recorded. When the calling subscriber hangs up, the common apparatus is released. When the absent subscriber returns and removes his hand-set, he hears a busy tone if no message has been recorded. Even if a message has been recorded, he must release the special equipment by operating 4DR by the use of key LK to release 4SSR1, 4FR before he can cause it to be reproduced. The release of FR makes a re-winding circuit for the common equipment and when the wire is fully re-wound, a circuit is made for two seconds only for a relay 4RR which applies ringing current to the line for that period unless the subscriber is using his telephone, in which case 4CR will be operated. To prepare for the reproduction, the subscriber dials a further 3-digit number which causes the operation of 4SSR2 as well as 4SSR1. This causes the immediate association of the common apparatus, Fig. 5, and CAR, 4BR operate in series, the latter releasing 4SSR1, 4SSR2. The line is now connected via shunted windings of 4ER and the A, B wipers of the finder to relays CER, CDR which operate. To find out if the recording wire is fully re-wound, the subscriber operates RWK to release CER momentarily. CFR1 pulls up and, when CER re-operates, CGR1 and, if the re-wind has not been completed, CNR operates and gives a tone signal. When reproduction is to begin, the subscriber momentarily releases CDR, but not CER with a key LK. This operates CFR2, CGR2, 4GR and the winding magnet are energized from a reversed battery so that on this occasion the wipe-out magnet the circuit of which includes a rectifier is not energized. CBR; CMR were energized on the operation of CER so that the amplifier is now in a direction to amplify messages picked up by the combined recording and reproducing magnet RT and pass them over wipers A, B to the subscriber's line. LK can be operated momentarily to stop the reproduction by operating CHR2 which brings down CFR2, CGR2. A further brief operation of LK re-operates CFR2, CGR2 to cause the reproduction to begin again. RWK can be operated in a similar manner to cause the wire to be re-wound. When all the messages have been reproduced, a contact-operating member carried by a carriage moved in proportion to the amount of wire wound off again comes up against a heavy member RB which it moved to a corresponding extent during the recording operation and completes a tone circuit. When the subscriber hangs up, the apparatus is released and the wire is rewound. If the subscriber wants to hang up before hearing all the messages, he operates key AK, releasing 4ER which holds 4GR to prevent re-winding when the circuit is released. If an incoming call arrives during reproduction, the ringing current is heard via, condensers C3, C4. The subscriber accepts the call by operating AK. In these circumstances since terminal c1 is grounded by the cut-off relay, the relapse of 4ER energizes 4AR which locks, bridges the a and b wires to stop the ringing current and substitutes large condensers C5, C6 for the condensers C3, C4. On the re-operation of 4ER, the tripping bridge is removed. The called line is fed with microphone current via relays CER, CDR. When the calling party hangs up, 4AR falls and reproduction can be resumed.