Patent GB-223721-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1923-10-04
Abstract: 223,721. Coventry Automatic Telephones, Ltd., and Collyer, J. E. Oct. 4, 1923. Automatic and semiautomatic exchange systems. - A co-ordinate switch is arranged at the end of its movement in one plane to take a step automatically in the other plane, .and the bank terminals thus engaged are associated with means to determine the subsequent operation of the switch. The invention is described with reference to a Strowger connector in a Private Branch Exchange, the tenth level being connected to trunks to the main office, but is equally applicable to the type of switch in which the rotary movement comes first and to connectors in a main office on which the lines to a P.B.X. occupy several levels. Operation as a connector. Relays 9, 10, 11 pull up when the switch is seized, for example by the line switch described in Specification 208,075, and the first digit is repeated to vertical magnet 4. The change-over of off-normal springs V.O.N. energizes relays 14, 16 and arranges for the relapse of relay 71 at the end of the digit. When relay 11 falls back, rotary magnet 5 pulls up over 34, 30, 27, and releases relay 14 whereupon magnet 5 itself is released. The terminals reached by this step are dead. The units digit operates the rotary magnet 5 and on the first step, springs R.O.N. change over so that relay 16 falls back at the end of the digit. If the wanted line is busy, relay 15 energizes and the relapse of relay 16 sends back busy tone from 43. If relay 15 does not energize, relay 16 extends the c-wire to operate the wanted cut-off relay and relay 18 energizes sluggishly because of its short-circuited lower winding and sends out ringing current from 50. The energization of ring trip relay 17 supplies talking current to the wanted line over impedance 13. The calling line is fed over relay 9, the release of which by the calling party releases the connector. Operation to select an idle main office, trunk. In the tenth level the c-terminal of the set reached by the automatic rotary step is grounded so that relay 15 pulls up and energizes relay 12 which looks up and connects the stepping relay 14 to the c-wiper 3. Relay 14 pulls up and energizes, and is then released by rotary magnet 5 which it releases. Stepping continues until an idle trunk is found, relay 16 being held up by relay 14. When an idle line is reached, relays 15, 16 fall back and relay 18 sends out ringing current as described above. The last terminals may be associated with a busy signal instead of an outgoing trunk, or shaft springs may be operated to send a signal when the wipers move beyond the last terminals. Modifications. A marginal relay may be connected in series with relay 15 and the first terminals may in some levels be grounded through a resistance and in others direct or not at all. The additional discrimination furnished by this may be used to control a meter in some levels. In the case of a connector on which lines to a P.B.X. occupy several levels, it may be arranged that when a level is completely busy the first terminal is marked so as to cause the wipers to be released and given a further vertical step.