Patent GB-272461-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1927-04-29
Abstract: 272,461. Associated Telephone & Telegraph Co., (Assignees of Stehlik, R. F.). June 14, 1926, [Convention date]. Automatic exchange systems.- The line wipers of a Strowger call finder are moved into engagement with the selected terminals by a further energization of the vertical magnet which remains operated throughout the connection. The circuit of the vertical magnet at this stage is made and maintained by the release magnet which, when energized, engages the double dog but does not withdraw it. The invention is described with reference to a system, in which a pre-selected finder associated with a forwardly hunting secondary switch is set by impulses representing the calling number. If the secondary switch has not found a group selector when the finder reaches the line, the link is released and a new one allotted. If the calling line is seized by a connector before it is found, the line wipers are not moved into engagement with the terminals and the link is released, this operation being controlled by a fourth wiper which engages the test terminals ,during movement of the finder and is kept in engagement with the calling one after the switchthrough. Other features of the system are claimed in Specification 281.303. Marking arrangements. The subscriber A is numbered 55 and when he calls, the 5th level-marking relay 314 pulls up over 186, 195, 188, 429 and locks itself over relay 309 which disconnects the first five level-marking relays, energizes relay 315 which disconnects the second five, energizes relays 301, 108 which disconnect the wire 188 from the wires. 195. 196 &c., and energises relay 107. Relay 314 grounds the first five terminals in the first half of the middle bank of switch SO and completes a circuit over the loop for the 5th line-marking relay 114 which grounds the first five terminals in the second half and locks un in series with relav 109 which with relay 302 disables the line-marking relays. Relay 302 also energizes the starting relay 407 which at 435 holds the marking relays, the ground - at 429 being removed by relay 404 which pulls up sluggishly on the energization of relay 107. Setting finder. Relay 407 extends the ground on 422 to relay 403 which sends an impulse over the transformer 402 to the vertical magnet 104 and energizes the back stroke driving magnet 401 of the counting switch. Magnet 401 opens the energizing circuit of relay 403 and when the vertical magnet is fully energized, this relay falls back and the magnet 401 moves the wipers and re-energizes relay 403. After five impulses the wiper 422 reaches an ungrounded terminal and relay 403 is not re-energized but .completes a self-interrupting circuit lor magnet 401 which drives the counting switch until the wipers reach the second half of the bank wuereupon relay 403 pulls up again and a second digit is sent, this time, over 251 to the. rotary magnet 103. Secondary switch SS and switch through. Relay 407 over 252, 255 completes an interrupter circuit from the driving magnet 105 of the back-stroke switch SS to test wiper 129 and connects ground over relay 408 to the junction point. When an idle line is found, relay 408 pulls up, locks Itself and energizes the release magnet 103 which extends wire 172 (which is grounded by relay 408) over resistance 158 to the test wiper to mark the group selector busy, and also connects the test wiper over resistance 157 to the vertical magnet 104 which cannot pull up in series with both resistances. After sending the second digit, the switch SQ goes automatically to its final terminals to energize relay 409. When relays 408, 409 are both operated, direct ground is connected to wire 177 and the vertical magnet is energized over 157 sufficiently to move the finder wipers into contact with their terminals whereupon the cut-off relay 101 pulls up. Dialling tone goes back from the transformer 210. Should a conector seize the calling line before the finder is ready to switch through, the earth on terminal 165 short-circuits relay 409 and the finder cannot switch through. The allotting switch however is moved on as described below and the magnet 103 then falls back and releases the finder. If the secondary switch is unsuccessful relay 408 being unenergized, relay 409 is unable to complete the switch through circuit and a new link is allotted as described below. Restoration of common equipment; allotting switch FA. Relay 405 which is energized in parallel with relay 409 disconnects the relay 407 which, after an interval releases relay 408, energizes the magnet 401 over 423 to cause the sending switch to move one step to its home position, and releases relay 405 and relays 314, 309 which release the relays 114. 107 - - 109, 301 and 315. Relay 107 releases relay 404 and the mechanism is now restored to normal. The magnet 209 of the back stroke allotting switch FA which is energized in parallel with relay 405 falls back on the relapse of relay 407. If the finder now encountered is busy, the magnet 209 is energized in a self interrupting circuit over 256, 254, and continues to move the wipers until an idle finder is reached. All finders busy. The release magnet 103 removes ground from a common wire 179 connected to the lower winding of relay 405 and when the last release magnet pulls up, relay 405 is able to hold up over the winding after the relapse of the starting relay 407 to prevent relay 407 from being re-operated until a finder becomes available. The allotting switch rotates continuously.