1946. Betulander, G. A. Jan. 26. Automatic exchange systems in which both linewires are earthed at the subscriber's station during the process of establishing a connexion, the current in one line-wire being interrupted the number of times necessary to select the desired line. During the actuation of the connector, a detent-magnet is energized simultaneously with the operating- magnet, but after the connector has been brought into the desired position, it remains under the control of its operating-magnet only and is released when the latter is again energized. The subscriber's line-relays co-operate with a time-lag contact, included in the main battery lead, in such a manner that if the line is continuously earthed by a fault, the battery is automatically disconnected from the subscriber's line. The invention is described as applied to a system in which one of the subscribers is enabled to interrupt a conversation between two other subscribers and to connect himself to one of them. Construction of connector. The wipers 15,16, 38 are carried by the armature of a cut-out magnet 12 mounted on the framework 29 of the connector. The armature 22 of the operating-magnet 9 can only be attracted when a locking-magnet 11 is energized. The detent-magnet 10, which is always energized with the magnet 9 during the connecting operation, controls the normally-disengaged detent 30. General operation. Assuming that subscriber III wishes to call subscriber IV, he sets his impulsetransmitter to No. 4 thereby earthing both his linewires over contacts 5, 6, and then actuates his magneto, sending current through the relay 84 and condenser 85 at the exchange, thereby completing a circuit from the battery 27, through the time-lag contact 77, wire 25, magnets 12, 11, wire 90, contact 85, and then in parallel over the relays 71, 72 to earth at the sub-station. The relays 71, 72 (1) by attracting their armatures 79, 80 complete a circuit independent of the relay 84 from the wire 90 to earth at the substation, and (2) by attracting their armatures 81, 82, complete the circuits of the operating and detent magnets 9, 10. As the magnet 11 has been previously energized, the armature 22 moves the pawl 28 into engagement with the next ratchet tooth, the detent 30 holding the switch. The impulse-transmitter then interrupts the contact 3 four times, opening the circuit of the relay 71 and consequently of the magnet 9. The wipers 15, 16, 38 are thus moved to the contacts of the fourth subscriber. The earth-contacts 5, 6 are broken by the impulse-transmitter before the contact 3 is again closed after the fourth interruption, with the result that the relay 72 opens the circuit of the magnet 10, which withdraws the detent 30, so that the bar 29 is kept in its raised position only by the pawl 28. Busy test. The breaking of the earth connexion at the contacts 5, 6 opens the circuit of the cut-out magnet 12, thereby allowing the wipers 15, 16 to engage the contacts above which they have been placed, if the desired subscriber is disengaged. If, however, the wanted subscriber is engaged, the magnet 12 remains energized by a circuit including the test-wiper 38 and a roller 39 which engages the test-wires 121 ... 124 of the other subscribers. If the subscriber wanted is himself a called subscriber, the circuit of the magnet 12 will be completed from the battery 45 through the time-lag contact 77 of subscriber III, wire 25, magnet 12, wire 48, contact 42, test-wiper 38, test-wire 124, to the test-wiper 38 of the subscriber who has called the wanted subscriber, contact 41, and wire 43 to the battery 45. If the desired subscriber is himself a calling subscriber, his test-wire 124 is connected to the battery 45 through a wire 52 and a contact 49-50 closed when the switch 29 is not in its normal position. The magnet 12 may be connected in a local circuit controlled by the magnet 11. In order that a calling subscriber may receive an indication that the required subscriber is engaged, a spring 61 on the armature of the magnet 12 cooperates with a fixed contact 62 which is connected through a high resistance 63 to the wire 90. If the calling subscriber's wipers 15, 16 are resting on an engaged subscriber's lines, and he repeatedly closes the contact 5 of the sub-station apparatus, test currents will flow through his receiver over the following circuit from the battery 27, contact 77, wire 25, magnets 12, 11, resistance 63, contacts 62, 61, wire 66, and then in parallel over the relays 71, 72 and line-wires 1, 2 to earth at the substation. Ringing and talking circuit. The line-wires 1, 2 are connected by the wires 13, 14 to the wipers 15, 16, which normally rests upon leads individual to the particular station. The selected subscriber is called by operating the magneto, the ringing- current passing over the line-wires 1, 2, wires 13, 14, wipers 15, 16, leads 101, 114, of the called subscriber, the wipers 15, 16 of his switch, wires 13,14, and line-wires 1, 2, to the called station. The talking-circuit is similar. Release. At the end of the conversation, the calling subscriber restores his switch to normal by operations similar to those used in establishing a connexion, that is to say he first earths both linewires at contacts 5, 6, and then actuates his magneto to energize the relay 84, which in turn establishes a circuit through the relays 71, 72, and magnets 9, 10, 11, 12 as before. The armatures 22, 23 are thus attracted, and the lower end of the pawl 28 in riding over a ratchet tooth passes outside the upper end of the armature lever 23, as before. By opening the contact 4, the circuit of the relay 72, and consequently of the magnet 10, is broken, and the armature 23 in returning to its normal position forces outwards the pawl 28, thereby setting free the switch which returns to zero under the action of gravity. Arrangement by which subscriber I can interrupt a conversation and connect himself to either of the engaged subscribers. The individual leads 102-104, 112-114, 122-124 of the three subscribers II, III, IV do not extend beneath the wipers 15, 16, 38 of subscriber I, but are replaced by additional leads 132-134, 142-144, and 152-154. Assuming that subscribers III and IV are conversing, if subscriber I moves his switch wipers on to the leads 134, 144, 154 of subscriber IV, current passes from the battery 45, wire 26, time-lag contact 77 of subscriber IV, wire 25, magnet 12, wire 154, wiper 38 of subscriber I, contact 41, and wire 43 back to the battery. The magnet 12 of subscriber IV is thus energized, and raises its wipers 15, 16, 38, thus interruping the conversation between subscribers III, IV. The ringing and talking circuits between subscribers I, IV passes from the line-wires 1, 2 of subscriber I over the wires 13, 14, wipers 15, 16, leads 134, 144, contacts 55, 56 of subscriber IV, wires 59, 60, 13, 14, and line-wires 1, 2 to sub-station IV. Action of time-lag contact 77. In order to prevent waste of battery current should a line-wire be earthed through a fault, the contact 77 is inserted between the battery lead 26 and the magnets 9, 10, 11, 12, and is controlled by clockwork released by a magnet 88. The arrangement is such that the contact will be broken if current passes through it for a period which is longer than that required for the connecting operation, the contact being then immediately closed again. Thus, if an earth fault occurs in the line 2, the relay 72 will remain energized after the connexion has been effected, and the contact 77 will be opened after a certain period, thereby opening the holding-circuit of the relay 72, and consequently disconnecting the battery from the line.