393,583. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. Dec. 3, 1931, No. 33526. Convention date, Dec. 18, 1930. [Class 40 (iv).] In a semi-automatic telephone system, link circuits connect toll lines with subscribers' lines. Four types of link circuit are described for the following purposes : (1) to connect toll lines, reaching the link circuits over non- numerical selectors, with numerical selectors having access to other link circuits, other toll lines and ordinary subscribers' lines ; (ii) to connect numerical selectors, having access to ordinary subscribers' and toll lines, with numerical selectors of similar type ; (iii) to connect toll lines, extended over other link -circuits, with numerical selectors having access to toll and ordinary subscribers' lines, and (iv) to connect ordinary subscribers' lines, reaching the link circuit over numerical selectors, with numerical selectors having access to toll and subscribers' lines, arrangements being provided to extend party-line ringing to the link to recall the calling party. The final selectors are accessible to both ordinary lines and toll circuits, ringing being automatic if the connection is reached from an ordinary line and under control of the operator if reached over a link circuit. Coin-freed supervision and party-line ringing are provided. General operation. A toll line, terminating in line switch LS, Fig. 3, is extended to a free link L. The operator, Fig. 2, answers the call by throwing key K3 and, by setting up the number of the required circuit on either the key-set, Fig. 1, or the dial D, extends the call over the selectors, Fig. 4, to another toll circuit such as that terminating in LS2, Fig. 3a, to an ordinary line over selector TTS, Fig. 7, and connector C, Fig. 8. or to a further operator at PA1, Fig. 5, accessible over a further link L2, Fig. 9. The further operator can either extend the call over selector S3, which is similar to S, or can record the call. In the latter case the operator, when circuits are available, seizes a link such as L1, Fig. 6, and calls the two parties over selectors S1, S2. Should a subscriber such as T2, Fig. 11, wish to extend a call via an operator's position, his line is extended over line switch LS1 and numerical selector S5 to link L4 and the call is answered by the operator at PA2 by throwing key K18. This operator extends the call over selector S4, which is similar to S1. The calling party can be re-rung by setting the selector RC to the number of the link circuit L4 and then setting the auxiliary switch associated therewith to select the appropriate type of ringing to ring the calling party. The position apparatus PA1 is provided with a key K8 for supervision of coin-freed apparatus. The connector C, Fig. 8, is accessible to both ordinary selectors and toll selectors, such as TTS. If the connector is reached over TTS, ringing is withheld until started by the operator and speaking current is provided from TTS, a through metallic circuit being provided over C ; but if the connector is in use on a local call, ringing is supplied automatically and speaking current is fed from relays 802, 803, the condensers shown being retained in the line circuit.. Call from toll line to toll line. When the circuit 391, 392, Fig. 3, is seized and ringing is connected thereto, relay 302 operates and its 'armature 313 locks up until released by relay 303. Relay 305 energizes and magnet 306 steps LS, from earth on 335, until a free link, such as L, is reached. Relay 304 pulls up, extending the incoming conductors to the link and 353 energizes. Lamp L2 lights to indicate a call on link L and relay 354 pulls up. If the operator at position PA, Fig. 2, is too busy to deal with the call, key K4 is operated to release 304, and magnet 306 re-operates to step LS in search of another free link. To answer the call the operator moves K3 to the left. Relay 351 operates to extend the incoming circuit to the operator's position and locks in series with 352 and 203. Relay 303 operates to unlock 302 and 353 releases to extinguish L2. Lamp L1 lights to indicate the group of trunks over which the call originated and relay 354 lights lamp L3 to mark the link as busy. The energization of relay 203 connects the operator's telephone equipment OT with the link and connects earth to lead 28 to prepare the register circuit. The operator converses with the caller and ascertains that the call is to be extended to a trunk such as 391<1>, 392<1>, Fig. 3a, for which the selector S is to be set to level 4. The key 4 of the set KS is depressed to register the digit and the start key ST is operated. Relay 11 pulls up, locks in series with relay 12, and connects earth to conductors 29 and 30. Relay 13 pulled up when the first digit had been stored and relay 14 energizes. The connection of earth to conductors 29 and 30 allows relays 208, 209, 205 and 206 to pull up, lamp L lights, the outgoing end of the loop is extended by 205 to the impulsing leads 213, 2131, and relays 354, 355 energize over 214. The impulsing leads are thus extended to energize relay 402 of the selector S and relay 403 pulls up. Relay 502 of the sender now operates to remove the short across the impulsing contacts and four impulses are transmitted, whereupon 503 pulls up to close the loop. These four impulses are repeated by 402 to magnet 406 and the wipers are raised to the fourth level. Shortly after the receipt of the last impulse, slow relay 404 falls away, and magnet 407 interacts with relay 405 to step the wipers to a free contact. It is assumed that the circuit 384-386 is free and, when this circuit is reached, relay 401 operates to disconnect the relay 402 and to extend the link to the outgoing toll line 391<1>-392<1>, Fig. 3a. The relay 303<1> of the toll line will operate. In the register, Fig. 1, as the stored digit has been transmitted, ground is disconnected from 322 and relay 13 releases. Relays 11, 12 and 14 restore and relays 205, 206 and 209 fall away. Relays 205 and 209 are slow-release relays and during the period between the release of 206 and of 205 and 209, battery, via resistance 211, is connected over conductors 222, 380 and 386 to energize relay 301<1>, Fig. 3a, which connects a pulse or ringing current to the wanted exchange. The operator may talk with the called or calling party separately by moving either K1 or K2 to the left respectively and may withdraw from the connection by restoring K3. When K3 is restored, 351 and 352 fall away and 203 releases. Relays 354 and 355, however, remain locked to K4 and K3 respectively and hold the switch train. The operator may listen in' on the call by operating K3 to the right which connects her receiver to the line over induction coil IC. The operator may answer a call by means of the monitoring key when the sender is associated with another link. Under these conditions the relay 203 is held independently of the answering key K3 so that this key can be restored and the monitoring key of another .link operated. The relays 351, 352 of the second link will not be operated, but as the operator's telephone set is connected to the position apparatus, the operator can converse with the caller. When the sender is released the relay 203 releases and the operator's transmitter is disconnected, but the talking key of the second link can now be operated and the connection completed as described above. The operator can re-ring on either the called or calling circuits whilst K3 is operated by moving keys K1 or K2 to the right respectively. Battery is thus connected to 301<1> or 301 to connect a ringing pulse to the toll circuit. When the calling party rings off relay 302 energizes and 353 pulls up to light L2. The operator challenges the connection and releases by operating K4. Relay 354 falls away and 355 drops removing ground from 381 to release the selector. All trunks busy. If the selector had failed to find a free outlet, the switch would have been moved into its eleventh position and rotary cam springs operated. The busy flash interrupter is connected over 410 and 382 to 356 and lamp L4 flashes whilst busy tone filters back over condenser 440. Call from toll line to local subscriber. It is now assumed that the call is to be extended to a subscriber T, Fig. 8, and that the required routing number is 34568. As the operation of the register sender has been detailed above, it will be assumed that the connection is extended by the dial D. The operator answers the call as described above, key K20 is operated and the dial is moved to transmit the first digit 3. Off-normal contacts 270, 271 operate and perform the same function as the earthing of wires 29, 30. The first impulse train sets selector S to the third level and the link is extended over conductors 435-438 to the toll selector TTS, Fig. 7. When the dial returns to normal, 270 and 271 open and 208 restores. The short circuit round 207 is opened and this relay energizes in series with 707 to hold 205, 206 and 209. In TTS the operation of 707 allow 708 to pull up and prepare the impulsing circuit. The next impulse train is repeated by 707 to the vertical magnet 713 of TTS, relay 710 holding up during the train to short the upper left-hand winding of RC to improve impulse transmission. When the train terminates 710 releases and relay 711 and rotary magnet 712 interact to find a free final selector such as C, Fig. 8. Relay 709 operates to switch through the connection and 803 operates in series with the lower winding of 701; but 701 does not pull up. In the final selector relays 804, 806 and 807 energize. The third series of impulses is repeated by 707 and 803 to magnet 812, relay 710 energizing as before to improve the transmission loop, and the final selector wipers are raised to the fifth level. At the end of the train 807 falls away so that the fourth digit is repeated to the rotary magnet 813 and the wipers are moved to the ter