Patent GB-253625-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1925-03-23
Abstract: 253,625. Automatic Telephone Manufacturing Co., Ltd., (Automatic Electric Co.). March 23, 1925. Automatic exchange systems.-In a step-bystep switch adapted to hunt for an idle or marked one of a group of lines, when such line is encountered, the stepping magnet, if of the forward stroke type, is held energized during the response of the test or switching relay, to prevent the possibility of any further advance of the wipers. The response of the test relay subsequently de-energizes the stepping magnet. When the stepping magnet is of the back stroke kind its circuit is held open during the response of the test relay. The invention is described as applied to backwardly-hunting line finders and group selectors, two modifications of the former and eight of the latter being described. These modifications fall broadly into three classes, viz. (1) those in which the stepping magnet interrupts its own circuit, the interruption being rendered ineffective immediately an idle line is encountered, (2) those in which the stepping magnet is continuously energized over one winding and so long as busy lines are engaged is intermittently de-energized by an opposing current over another differential winding, and (3) those in which the magnet, upon energization and so long as busy lines are engaged, reverses the current through its winding to cause relapse. Line finder; first modification, Fig. 1. The response of the line relay 3 closes a. circuit over the start wire 45 for the line relay 6 of the first idle finder F, which completes a stepping circuit for the magnet 4 over its interrupter contacts 16. The magnet 4 advances the wipers at each forward stroke until the calling line is engaged, when earth over the test wiper holds the magnet 4 energized in series with a low resistance upper winding of the switching relav 5, thereby positively stopping the switch. The relay 5 locks over its lower high resistance winding, in series with the magnet 4 which now relapses. On the relapse of line relay 6, the start wire 45 is extended to the next finder, the switching relay being held by earth returned over wire 43. Second modification, Fig. 3. This modification is suitable for use with either a back stroke or forward stroke stepping magnet; the circuit of the stepping magnet is entirely local. In the first case the start relay 6<1> closes a circuit for the magnet 4<1>. which at its armature 16<1> closes a parallel circuit for a relay 7'. which opens the circuit of the magnet 4<1>, which in turn de-energizes the relay 7<1>. This cycle is repeated until the calling line is engaged, when the relay 7' does not fall away but holds over the test wiper 38<1> in series with the switching relay 5<1>, there by maintaining the circuit of the magnet 4<1> open. The switching relay 5<1> locks with the relay 7<1> to the release wire 43'. If the finder is arranged to advance on the forward stroke of the magnet 4<1>, the operation is the same with the exception that the testing operation is delayed until the magnet 4<1> falls back and releases armature 16<1>. Group selector; first modification, Fig. 2. The vertical movement is effected bv the vertical magnet 107 in the usual manner in response to the first digit, and on the relapse of the series relay 103 a circuit is completed for the rotary magnet 106 through the upper tapped portion of the exchange battery 140. The magnet 106 advances the wipers a step, inserts a resistance 100 in its circuit, and assuming the first trunk'to be busy, closes another circuit through itself in the opposite direction over 126, 116, 108, 121 to the lower part of the battery : resistance 108 prevents an excess of current during the instant that the three contacts of the magnet 106 are closed. The magnet 106 thereupon retracts its armature 121, short-circuits resistance 109, and opens the opposing circuit. The initial circuit of the magnet is now restored, but by the time the current flow has built up sufficiently to pull up the armature, the latter is fully retracted by its spring tension and acquired momentum. In this manner the wipers are advanced until an idle trunk is engaged, at which time the rotary magnet 106 remains held in series with resistance 109, and the switching relay 104, being no longer shortcircuited, energizes and locks over circuit 117, 109, 106, and opens the initial circuit of magnet 106, which drops back. On release, when ground is removed from wiper 126, the holding circuit of relay 104 is opened, and a circuit becomes effective in the opposite direction through its winding passing through the upper part of the battery and the holding relays at the preceding switching devices. The relay 104 relapses rapidly, disconnects the holding wire 43 to release preceding switches, and restores the selector in the usual manner. Second modification. This arrangement is very similar to that shown in Fig. 2, the main difference being that the switching relay is provided with two windings. When an idle trunk is engaged, the switching relay is energized over its upper winding and locks over both windings directly to the holding wire in a circuit including the whole exchange battery. During the response of the switching relay the stepping magnet is held as in the previous modification, its circuit being later permanently opened when the switching relay has pulled up. On release, the removal of holding earth de-energizes the holding relays of the preceding switching devices independently of the switching relay of the group selector. Third modification, Fig. 5. In this arrangement both the switching relay and the rotary magnet are provided with two windings. When the series relay relapses on the cessation of the first digit, the rotary magnet 202 is energized over its right-hand winding. As long as the test wiper 214 engages earthed busy contacts, the lefthand winding of magnet 202 and the lower winding of the switching relay 201 are short-circuited, and the rotary magnet interrupts its energizing circuit at armature 203. When an idle line is engaged, the switching relay 201 operates over its lower winding in series with the left-hand holding winding of magnet 202 and resistance 200; the magnet 202 is thereby positively stopped. Relay 201 locks to the release wire over its upper winding, and disconnects both windings of the magnet 202. Fourth modification. This arrangement is very similar to the last, but the lower winding of the switching relay and the holding winding of the rotary magnet are normally short-circuited over an armature and back contact of the magnet. On the energization of the rotary magnet this short-circuit is opened and is replaced by another short-circuit over the test wiper so long as busy trunks are engaged. Fifth modification, Fig. 7. A differentially wound rotary magnet is used in this arrangement. On the relapse of the series relay the rotary magnet 250 is energized over its left-hand winding and holds over resistance 252. If a busy trunk is engaged, the switching relay 251 is shortcircuited, but an opposing current flows over the right-hand winding of the magnet, which relapses and restores its original circuit. This cycle continues until an idle trunk is engaged, when the high resistance switching relay 251 energizes in series with the right-hand winding of the magnet. its high resistance preventing neutralization of flux and relapse of the magnet. Relav 251 locks up in series with the left-hand winding of the magnet, its high resistance causing the latter to relapse. Sixth modification, Fig. 8. This arrangement is similar to that shown in Fig. 2, but the requisite voltage for releasing the rotary magnet is obtained on the potentiometer principle. On the relapse of the series relay, the rotary magnet 314 energizes over circuit 305, 307, 311. If the next trunk is busy, current also flows over circuit 319, 313, 314, 309, 304 in the opposite direction and causes the relapse of the magnet which restores its original circuit. This cycle continues until an idle trunk is engaged, when the switching relay 301 being no longer short-circuited energizes over resistance 302. the magnet 300 being held during this over circuit 303, 309, 302. Upon responding, the switching relay 301 locks in series with the magnet and opens the holding circuit of the latter which de-energizes due to the high resistance of the switching relay. Seventh modification. This arrangement uses a differentially-wound rotary magnet and is similar to the modification shown in Fig. 7, but the switching relay has a low resistance energizing winding and a separate holding winding. As long as busy lines are engaged, the energizing winding of the switching relay is short-circuited and opposing current flows directly through the differential winding of the magnet to cause its relapse. When an idle line is engaged, a circuit extends over the energizing winding of the switching relay and the differential winding of the magnet. The switching relay pulls up, but the magnet is positively held, the differential winding being ineffective due to the resistance of the lower winding nf the switching relay. The switching relay locks to the release wire over its holding winding and disconnects the energizing winding of the rotary magnet. Eighth modification. This is similar to the arrangement shown in Fig. 7. with the exception that the switching relay locks over a separate holding winding.