Patent GB-191001418-A (GB)
Title: Improvements in or relating to Telephone Systems.
Inventor: MELLINGER EDWARD A
Filed: 1910-01-19
Granted: 1911-01-19
Abstract: 1418. Mellinger, E. A. Jan. 19. Automatic exchange systems.-In a system in which the selecting-impulses pass over the complete metallic circuit, no grounds being used at the sub-stations, the first selector is provided with a line relay which controls the selector in seizing an idle second selector, and then repeats the further set of selecting - impulses to the actuating-magnets of the second selector and connector, which have no line relays. In the system described, the microphone current for both the calling and called subscribers, the busy signalling current, and the ringing-current are all supplied from the first selector. The invention is described as applied to a system in which each subscriber's line terminates in an individual switch C. and a group of such switches is controlled by a master switch D, which maintains all the disengaged switches in readiness to make immediate connexion with an idle first selector E, in the same general manner as is described in Specification 26,301/06. Subscriber's individual switch. Each switch comprises a plunger (not shown), a trip magnet 18, release-magnet 19, and cut-off relay 20, as described in the above-mentioned Specification. When the magnet 18 is energized, the plunger is thrust into the bank of contacts and forces the springs 21, 23, 25, 27 into contact with the springs 22, 24, 26, 28, respectively. In their normal position, the plungers of a group of such switches are engaged by a shaft controlled by the master switch. D, which is rotated by a self-interrupting motor magnet 29 and a ratchet 30, the rotary motion of the ratchet being transmitted to the plunger shaft so as to give the latter a reciprocating movement. In order to stop the plunger shaft with the plungers resting exactly over a set of trunk terminal, a pair of springs 35, 36 rest upon the periphery of a notched wheel 34, and keep the circuit of the magnet 29 closed until the plungers are directly over a trunk, when the spring 36 drops into a notch and opens the circuit of the magnet 29. A wiper 38 on the plunger shaft connects a common contact 37 successively to a number of test contacts 82, connected respectively to the third springs 26 of the respective trunks. When a calling subscriber A removes his receiver, current flows from the battery lead 80 over a contact 78-77, trip magnet 18, contact 76-75, line 17, substation apparatus, line 16, and contact 74-73 to earth. The magnet 18 releases the plunger of the switch C, thus bringing the springs 21, 23, 25, 27 into.contact with the springs 22, 24, 26, 28, respectively. The closing of the contact 27-28 earths the test lead 81 of the calling-line, and also closes a circuit through the cut-off relay 20, which disconnects the trip magnet 18 from the line-wires. The closing of the contact 25-26 closes a circuit from the battery lead 80 through the release magnet 19, contact 25-26, contact 82, wiper 38 (then resting on contact 82), contact 37, and relay 31 to earth. The high resistance of the relay 31 prevents the energizing of the magnet 19, but the relay 31 is itself energized and closes the circuit of the motor magnet 29, which rotates the master switch until the wiper 38 engages the unearthed contact of an idle trunk and thus opens the circuit of the relay 31. Exact adjustment of the plunger shaft is ensured by the springs 35, 36, as previously explained. A slow-release relay 32 in parallel with the magnet 29 opens the circuit of all the trip magnets 18 while the master switch is in motion, and should a further calling subscriber remove his receiver at this moment, he will receive a busy signal from the busy transformer J over the contact 79-77. First selector. The closing of contacts 21-22, 23-24 completes a circuit through the calling station for a quick-acting relay 39, which energizes a slow-release relay 91, and this in turn opens the circuit of the release magnet 50, connected through the off-normal springs 96 to the battery lead 80. When therefore the subscriber sends the first set of selecting-impulses by interrupting the line circuit, the relay 39 repeats them over a circuit from ground G<6>, through the contacts 88-89, 93-92, side-switch wiper 43, vertical magnet 40, and slow-release private-magnet relay 95 to the battery lead 80. The magnet 40 raises the wipers 47, 48, 49 to the terminals of the desired group of second selectors. The slow-release relay 95 is energized by the first impulse and closes a circuit for the private magnet 46, which is deenergized, so as to move the side-switch into its second position, when the relay 95 is no longer energized by the selecting. impulses. In the second position of the side-switch wiper 45, the battery lead is connected to the rotary magnet 41, which steps round the selector until the wipers reach the terminals of an idle trunk. This hunting movement is controlled in the usual way by the private magnet 46, which remains energized over a circuit which includes the lower winding of a relay 52 so long as the wiper 49 engages earthed terminals. The high resistance of the magnet 46 prevents the relay 52 from being energized at this stage. When the side-switch moves into its third position, the test wiper 49 is earthed through the lower winding of the relay 52, thus completing a circuit for a relay 153 of the second selector. The relay 52 still remains inactive, but the relay 153 opens the circuit of the release magnet 58, which is connected to the battery lead through the off-normal springs 133. The side-switch wiper 104, Fig. 1, in its second position supplies current to the lower winding of a relay 42, which energizes so as to prevent premature excitation of the ringing-relay 51 when the side-switch passes to its third position. The circuit of the relay 42 is then maintained by a current over the trunk 101. Second selector. The second set of selecting- impulses are repeated by the relay 39, Fig. 1, over a circuit from ground G<6> through the contacts 88-89, 93-92, wiper 43, contact 108-109, trunk 100, vertical magnet 55, and the slow-release privatemagnet relay 63 to the battery lead 80. The magnet 55 raises the selector wipers to the desired row, and the relay 63 causes the private magnet 57 to move the side-switch into its second position as before. The rotation of the selector to find an idle connector is effected by the rotary magnet 56 and private magnet 57 in the usual way. When the side-switch wiper 61 moves into its third position, the ground on the wiper 49 is extended to the wiper 114, thus energizing the release relay 72 of the connector. Connector. The third set of selecting-impulses are repeated, as before, by the relay 39, Fig. 1, and pass over the trunk 100, wiper 115, Fig. 2, privatemagnet relay 154 and vertical magnet 64 to the battery lead. The magnet 64 raises the connector wipers to the desired row, and the relay 154 causes the private magnet 67 to move the side-switch into its second position as before. The final set of selecting-impulses is consequently repeated to the rotary magnet 65, which brings the connector wipers to the contacts of the required subscriber. Busy test and busy release. If the required line is engaged, its test contact 121 is earthed, so that when the armature of the private-magnet relay 154 falls back after the last rotary impulse, a circuit is completed through a relay 128, which thereupon connects the battery lead 80 directly to the wire 119, test wipers 114, 49, and the lower winding of the relay 52. The connexion of the battery directly to the wipers 114, 49 short-circuits the release relays 72, 153, and supplies the relay 52 with sufficient current to energize it. The relays 72, 153, upon de-energizing, close the circuits of the release magnets 66, 58, respectively, these circuits being opened by the off-normal springs 120, 133 when the switches have returned to their normal position. The relay 52 (1) closes a locking- circuit through its upper winding and the contact 89-90 of the relay 39, (2) completes a circuit for the release magnet 50, and (3) connects the busy generator J over a contact 134-135 to the calling line. When the calling subscriber hangs up his receiver, the relay 39 is de-energized, and opens the circuits of the relays 52, 91. When all three relays have de-energized, a circuit is completed from the battery lead 80 through the release magnet 19, slow-release relay 143, contact 141-142 of this relay, and contacts 138-137, 94-93, 88-89 to earth. This circuit is broken slowly by the relay 143 so as to allow the magnet 19 to withdraw the plunger of the individual switch C, thus restoring the switch C to its normal condition. Supply of ringing-current. If the required subscriber is disengaged, the private-magnet relay 154, after the last rotary impulse, opens the circuit of the private magnet 67 so that the side-switch moves into its third position, in which the wiper 70 earths the test wiper 121, thus energizing the cut-off relay 144 of the called subscriber so as to prevent the operation of his individual switch when he removes his receiver to answer the call. The movement of the wiper 69 into its third position cuts off the battery from the trunk 101, thereby de-energizing the relay 42, Fig. 1, so as to connect the battery lead to the ringing-relay 51, which intermittently bridges the generator I across the called line. When the called subscriber removes his receiver, current flows through both windings of the relay 42, which is again energized and cuts off the ringing-relay. Release. When the calling subscriber replaces his receiver, the relay 39 is de-energized and opens the circuit of the relay 91, which in turn closes (1) the circuit of the release magnet 19, as previously described, and (2) the circuit of the release magnet 50. The release of the selector E removes the holding-ground G<8> from the release relays 153, 72 of the selector and connector respectively. The relays 153, 72 close the circuits of the