Patent GB-464338-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1935-10-15
Abstract: 464,338. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd. Oct. 15, 1935, No. 28455. Convention date, Nov. 30, 1934. [Class 40 (iv)] Link circuits at toll operator's positions, used in common for all incoming, outgoing and through long-distance calls, terminate in answering and calling single-motion switches, the former giving access to groups of long-distance lines and to local calling circuits and the latter to the same groups of long-distance lines and to circuits for completing incoming calls locally. The calling switches are controlled in the selection of a free line in a particular group of long-distance lines by a two-motion bypath switch associated with an operator's position and responsive to one or two digits from the operator's dial. For incoming calls, the hunting operation for an idle local toll-service circuit takes place automatically on the depression of a particular key. Means are provided for transferring a call from one line to another when the one in use proves faulty. Outgoing call ; connection of calling trunk LD to link L1. Relays 202, 203 operate connecting a special tone 211 to the calling line and grounding lead 212 to energize relays 507 at both operator's positions. Lamps 523 light and the operator at the position shown, say, operates key K1 of an idle link L1. Relay 303 operates, splitting the link and locking in series with relay 502 which connects up the operator's head set and prevents the operation of any other relay 303 if a further key is inadvertently thrown. Ground on lead 535 is extended over lead 341 to magnet 310 of switch AS which hunts for the calling trunk. When this is reached, relay 506 operates over leads 535, 352, 208 in series with cut-off relay 204 which cuts off tone 211 and grounds the test wire 222 to place release under the control of the operator. Relay 506 cuts the drive and operates 504 which energizes buzzer 503 and connects it to the head set to give a short tone-signal to the operator. Relay 504 also connects battery to lead 342 to operate relay 301 which locks in series with magnet 310, lights busy lamp 336, and connects direct ground to lead 352 to short-circuit 506. After an interval, relays 506, 504 release and 505 operates to light lamp 331 indicating a call from a local line. (When no calls are in progress, a key K1 may be left depressed so that the operation of relays 303, 502 occurs automatically when a call is made.) Selection of and connection to idle longdistance junction TL. The operator, having ascertained the wanted number, throws dialling key K15 to operate relay 519 which extends conductors 557, 558 to bypath switch BPS and bridges a coil 520 across them. In the switch BPS change-over relay 603 operates connecting up 604 which locks and completes the circuit for the line relay 601. When the dial CD is operated, off-normal springs 561 energize relays 509, 510 which connect the impulse springs 562 across the loop in place of coil 520. Impulses representing two digits are repeated to vertical and rotary magnets 615, 616, and on the release of relays 604, 605 a self-interrupting circuit is completed for the, rotary magnet. If no idle junction in the selected group is available, relay 606 operates, either over a strap between the contacts engaged by wipers 634, 635 when the last line is in the middle of a level, or over overflow contacts 614 when the last line is at the end of a level, to connect up busy tone 636. If an idle junction is found, relay 607 operates over wiper 633 and battery on lead 363 through cut-off relay 103, Fig. 1, and a parallel resistance 105. Relay 607, by grounding lead 354, causes magnet 320 to advance switch CS in search of the selected junction which is marked by ground over lead 363 and battery over leads 364, 555, and test relay 518. The latter operates quickly due to its upper priming winding, disconnects magnet 320, and operates relay 304 which switches through the link circuit. Large groups of junctions may occupy the whole of one level of BPS, in which case a circuit for rotary magnet 616 is closed over level springs 613 as soon as relay 603 falls back. The locking circuit of relay 604 is broken by 605, but a further temporary locking circuit is provided over resistance 608 and back contacts of the magnet to ensure that the wipers take a full step. Completion of connection ; supervision; release. The distant operator is rung by operating key K11, relays 509, 510 operating as during dialling, and when a reply is received the local operator restores key K15 and switch BPS returns to normal. Either end of the connection may be spoken to separately by the operation of a split key K12 or K6. When the connection is satisfactorily established, key K1 is restored and the talking circuit goes directly through link L1. The call may be monitored by throwing key K1 to the right, connecting the talking circuit over conductors 347, 348 to the operator's headset. At this time, relay 501 is operated to replace transformer 531 by 532 to reduce the energy loss, and the chief operator's supervisory equipment COE is connected in parallel with the receiver R instead of with the whole headset. If the transmission is unsatisfactory, the line may be changed by operating key K1 to notify both subscribers and request them to wait, ringing the distant operator by throwing key K11, controlling switch BPS as before to select another line in the same group, the corresponding switch at the distant exchange at the same time selecting the same line, and throwing key K14 to short-circuit relay 304 whereupon switch CS makes connection with the new junction. When the calling subscriber hangs up, relays 202, 203 release and light lamp 335. The operator throws keys K1, K8 whereby relay 301 is shunted over lead 342 and released, in turn releasing relay 204 and the calling circuit LD. Key K11 is then thrown to ring the distant operator and K14 short-circuits 304 to disconnect the called end of the link. If an operator is unable to complete a call at first, the calling subscriber may hang up and be recalled by the operation of key K4. Battery on the tip conductor at this key operates relay 201 which completes a through metallic circuit for the ringing current. Incoming call. Ringing current incoming over junction TL operates relay 101 which removes a short-circuit from 102 whereby ground is placed on start lead 212 and lead 108 is marked as calling. Switch AS of an idle link operates as for an outgoing call and when the operator gets the signal from buzzer 503 she throws key K16 which operates relays 515, 516. Relays 509, 510 operate, the group of local toll-service circuits TSC is marked over lead 358, and magnet 320 is connected up over leads 354, 535. When an idle circuit is reached, relays 513, 512, 514 operate, relay 304 is energized over lead 355, relays 509, 510 are released, and lamp 524 is lit to indicate that the operator may dial. In the circuit TSC, relay 401 operates over leads 373, 354, and marginal relay 511, inserting the repeating coil 402 and completing an outgoing loop from polarized relay 403 over conductors 406, 408. At each operation of dial CD relays 609, 510 operate over off-normal contacts 561 and release 401 to provide a metallic through circuit, and impulses are transmitted over leads 351, 356. If the called line is idle, a reversal of current operates relays 403, 404, and the shunting of the lower winding of 401 operates relay 511 whereby lamp 337 is lit. The called party is rung by throwing key K11 and when he replies, current is disconnected from conductors 406, 408 so that 403 releases and lamp 337 is extinguished. Key K1 is restored and during conversation lamp 337 is connected directly to lead 373. At the end of conversation, lamps 335, 337 light, and keys K1, K7 are thrown to shunt relays 301, 304. If the distant operator wishes the junction to be changed, she rings over it causing relay 302 to operate and light lamp 335. The local operator selects an idle junction in the required group in substantially the manner already described, but with key K13 thrown instead of K15 so that relay 517 is energized and the marking circuits are so modified that the switch AS instead of CS hunts for the junction selected by BPS, key K8 being first thrown to release relay 301. The circuit arrangements of Fig. 8 may replace those of Fig. 7 when the local switch train is used for incoming- calls instead of a special toll-service switch train. Through calls. Connections between two long-distance junctions are completed through a link L1 in substantially the manner described above. - Delayed calls. If a call when originated cannot be completed, the calling subscriber may hang up. The operator, in making a subsequent attempt to complete the call, takes into use a link by throwing key K1, re-calls the originating party over switch CS with key K16 thrown, and then controls BPS with K13 thrown to cause AS to connect to an idle junction. The operations are similar to those already described. Specification 393,583 is referred to.