Patent GB-253578-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/523
Filed: 1925-03-13
Abstract: 253,578. Western Electric Co., Ltd., (Deakin, G.). March 13, 1925. Semi-automatic and manual exchange systems; metering.-In a call-distributing system any subscriber at the exchange may be directly connected to any idle cord circuit at an occupied A-position and the positions may be left in any order. The cords of each position are divided into independent halves arranged so that there can be only one attended or waiting call on each halfposition. The switches are prevented from starting if they cannot give access to an immediately available cord, and in these circumstances lamp indicators are lit. Except under certain metering conditions, the calling party is released as soon as he hangs up his receiver. Means are provided for preventing metering and for repeated metering. Provision is made for extending calls through a distant automatic exchange and for breaking down local in favour of toll calls. In the system described, each group of 100 subscribers is served bv five of a total of 350 link circuits. The link circuits which comprise a 100-point power driven call-finder and a 100-point power driven cord selector, are allotted by a sequence switch having three home positions, the order of choice of the link circuits depending on the position from which the switch starts. There are seven A-positions, each having twenty cords. The total number of cords is divided into two main groups of seventy, cords from each group appearing evenly in all the half-positions. The link circuits are divided into corresponding groups and each of the sub-groups of five consists of three of one group and two of the other. Starting arrangements. The starting of any allotting switch is controlled by its relay 18, Fig. 1. The circuit of this relay includes out-of-order contacts 8. and contacts z for each of its link circuits, and the relay can thus be energized only if one or more of its link circuits are idle. The contacts z are connected to ground over back contacts of relays such as 23 belonging to the corresponding main group of cords. The relays 29, 30, are normally energized over y to which are connected in parallel a number of circuits (one for each cord in the group) such as 32, x, w, 51, v. This circuit is broken at x or w, or both while the cord is actually in use or plugged up after a conversation, at 51 if the cord is out of order and at v if the operator is away from the position or if there is a waiting or attended call on the half position in which the cord appears. Consequently if no cords are available in the group relays 29, 30 fall back and the relays 23 &c. remove ground from all the contacts z in the corresponding group of link circuits, and if there are no cords in either group the relay 18 cannot be energized. Extension of call to idle cord circuit. Line relay 1 energizes group starting relay 17 which energizes relay 18 if there are cords available, over the circuit described above, and allotting switch 20 moves from its home position. If the first link circuit is idle and gives access to available cords, relay 18 will be held up over D, F, or H (according to the starting position) and the switch stops. Otherwise, relay 18 falls back and makes a driving circuit over B. When an idle link is found, relay 18 stops the switch. Relay 7 of the idle link is now able to pull up in series with relay 18 since the resistance R1 is cut out, and completes driving and test circuits for the call-finder 5. When the line is found, relay 6 stops the finder and starts the cord selector 9. When an idle and available cord is found, relay 10 pulls up over h, x<1>, y', 51, 55, v', and shunts its high resistance winding by its low resistance winding in series with that of relay 11 to mark the cord busy. Relay 11 energizes relay 12 which makes the link circuit non-selectable, extends the talking and test wires and completes one half of the circuit of lamp 14, the other half being made at will by a key 15. Cut-off relay 2 pulls up in series with relay 70 in the cord circuit. Relays 1, 17, 6, 7, 18 fall back and the switch 20 moves to its next home position. Simultaneous calls. If simultaneous calls are made in the same group, one has to wait until the other has been connected to a cord, since only one link circuit in the sub-group can operate at one time. If two link circuits simultaneously pick up the same cord, both the relays 10 pull up initially but are unable to hold up over their low resistance windings. Generally, one falls back first, enabling the other to hold up, but where they both fall back, one will pull up again before the other. Should several link circuits be hunting when there is only one cord available, the finding of the cord by one of them and the consequent energization of the relay 23 &c. and relapse of the relays 7 disables the remaining link circuits. If there are cords in the other group, unsuccessful lines will be connected instantly to link circuits serving that group. No cords available. In these circumstances since relay 18 cannot pull up. the energization of relay 17 does not start the allotting switch, but instead, lights the lamps 21, 22 and energizes relay 19. When the subscriber hangs up again, relay 19 holds up momentarily after the relapse of relay 17 and causes the switch to leave its present and move to its next normal position. Position busy-arrangements. Simultaneous calls on the same half position. When a position is occupied, the contact J is closed, and in the absence of attended or waiting calls, relay 68 for one half position and relay 69 for the other energize each a group of relays 64 - - 66. These relays, over contacts such as v, close a number of circuits (one for each cord) to the wire y (and the corresponding wire not shown of the other main group of cords) to control the starting arrangements as described above, and over contacts v<1> and relays 55 - - 57 &c. make the idle cords selectable by the cord selectors over circuits such as v<1>, 55, 51, y<1>, x<1>, 32, h. When the cord selector wipers are switched through, the relay 55 &c. of the selected cord energizes relay 70 which locks up the relay 55 &c. and marks the half position busy by releasing relay 68 which releases relays 64 - - 67. The relay 55 is not unlocked until relay 44 pulls up in response to the insertion of the calling plug. The circuits of the relays 55 &c. are arranged so that only one can lock up at a time and if two switches seize simultaneously different cords on the same half position, only the lower of these relays locks up and the unsuccessful switch continues to hunt. Association of operator's set. Relay 70 energizes the driving magnet 63 of a seven-wipe. power driven finder switch associated with the operator's set. When the cord is found, relay 61 pulls up over wiper s to a contact of the relay 55 &c. and energizes relay 59 to connect up the set. Relay 75 (or 74 according to the half position) pulls up over wiper g, lights the pilot lamp 77, and connects the interrupter 76 to the line lamp 58 which has hitherto been burning steadily. The operator receives a momentary tone signal from TF over a contact of a sluggish relay 62 which is energized by relay 61 and released by relay 75. If the calling party is slow in answering, and there is a waiting call on the other half position, the operator momentarily depresses key 33 to energize relay 60 and release relay 61, thus re-making the driving circuit for the finder, which then hunts for the other cord. The operator can connect herself to any cord at will by a permanent pressure on the corresponding key 33. This marks a terminal in the bank of wiper t and gives control to that wiper in place of wiper s. Completion of local connection. The operator tests the wanted line with the tip of plug 43, and if it is idle plugs in. Relay 44 pulls up and relay 55 falls back, extinguishes lamp 58 and releases relay 61. Relay 50 pulls up, locks itself and connects holding battery to the wire g before relay 55 has time to fall back. The called supervisory lamp 39 lights up. Relay 42 pulls up and connects ringing current to the line. If the call is abandoned at this stage, relay 47 falls back and releases relav 42. Otherwise the reply of the called subscriber energizes relay 40 which removes a short circuit from relay 41. Relay 41 locks un short-circuiting relay 42, which then releases relav 40. Relays 37. 38 pull up and lamp 39 goes out. When the calling party hangs up, relays 35, 36 fall back, followed bv relay 47 and lamp 34 lights up. Relay 47 frees the link circuit and releases relays 41, 48. When the called party hangs up, relays 37. 38 fall back, lamp 39 lights up and the operator removes the plug releasing relays 44. 40. Calls to distant automatic office. The operator call by means of a keyboard. The same cord circuit is used as for local calls, but relay 40 is energized initially to prevent the application of ringing current to the line. If the wanted line is busy, the a-wire is intermittently closed to flash lamp 39 and a tone signal is sent back. Suburban calls completed over distant manual office; repeated metering. The call is set up in the same way as a local call, but the repeated metering key 45 is thrown. This puts a special tone on the calling sleeve and locks up relay 47 independently of relay 36. Relay 40 pulls up in series with relay 82, Fig. 4. on the distant office to stop the ringing. Relay 80 pulls up (in series with relay 38 which does not pull up and lights the line lamp 59. The insertion of the answering plug energizes relay 84 which connects relay 82 to 24-volt battery in place of ground, thus causing relays 82, 37 to pull up. Relay 83 pulls up over relay 88 (which remains unenergized) and energizes relay 81 which locks up and puts out lamp 89. To operate the subscriber's meter the suburban operator presses key K at intervals. This releases relay 83, which short-circuits the high