Patent GB-218392-A (GB)
Abstract: 218,392. Western Electric Co., Ltd., (Western Electric Co., Inc.). April 6, 1923. Automatic exchange systems.- Relates to a system in which 200- point Strowger-type switches are used as call-finders, group-selectors, and connectors. A single relay determines which set of wipers is to be used and, in the case of the connector, is operated or not according to the level in the preceding selector over which the connector was seized. The callfinders and group selectors are arranged to test lines simultaneously in pairs. In the 100,000-line system described, the 3rd, 4th, and 5th digits are repeated by relays at the second selector to the stepping magnets of the third selector and connector, and both parties are fed with taking current from the second selector. Call-finder, Fig. 1. When substation X removes his receiver, line relay 161 energizes group relay 100 which marks terminal 103, locks up, and energizes relay 102 to prevent control of relay 100 by other substations. Relay E, which is energized in a circuit 134, 105, 108, energizes vertical magnet 109 and series relay C. Magnet 109 on energizing releases relay E which releases magnet 109. Relay E and magnet 109 alternately energize and release each other until group wiper 112<1> finds the terminal 103 and the energization of relay A cuts out magnet 109 and relay C. Relay A also locks up, and energizes brush choosing relay B. Relay C on relapse associates rotary magnet 110 with stepping relay E. While the wipers are passing over pairs of which neither line is calling, relay B is held from ground on wiper 122 and relay E re-energizes over wiper 130, but when the pair containing the calling line is reached, relay E does not re-energize, since either there is no ground on wiper 130, or the relapse of relay B disconnects relay E from wiper 130. In the case assumed relay B remains operated. Relay D, the upper winding of which is no longer short-circuited, energizes in series with relay E (which, however, does not energize) grounds wires 118, 127 to lock up relay B, mark the line non-calling to other finders and energize cut-off relay 162. Relay D also extends the start wire 134 over wire 143 to the next idle finder and connects its lower winding to the start wire so that in case release occurs while another finder is operating over the circuit 134, 143, relay D does not fall back. First selector, Fig. 2. Energization of relav 100 energized the impulse relay IR, Fig. 2, which energized slow relav T<2>. On the relapse of relay 100 IR remains held up over both its windings and the calling loop and dialling tone is sent from transformer 204 over the non-inductive righthand winding. The first impulse energizes relay E<2> which energizes the vertical magnet 205 and series relay C<2>. At the end of the stroke magnet 205 releases relay E<2> which releases magnet 205 and is then energized by the second impulse. Relay C<2> energizes relay F<2> which locks up and energizes brush choosing relay B<2>. On the relapse of relay C<2> at the end of the digit the rotary magnet 214 energizes and at the end of the step releases relay F<2> which releases magnet 214. If now both the trunks engaged are busy relay B<2> is held up by the ground on wiper 228 and ground on wiper 236 re-energizes relay F<2> to cause a further rotary step. If either trunk is idle relay F<2> fails to re-energize, either because its circuit is broken by the relapse of relay B<2> or because there is no ground on wiper 236, and the wipers stop. Switching relay D<2> being no longer short-circuited energizes in series with relay F<2> (which does not pull up), locks up relay B<2> (if necessary), releases relay IR, and connects itself and relay B<2> to the c-wiper. Second selector, Fig. 3. When the selector is seized, relay I<3>R<3> energizes in series with the non-inductive upper winding of relay 303 and energizes slow relay T<3> to hold the operated relays at the first selector. The second digit is repeated by relay I<3>R<3> to relay E<3>, which co-operates with vertical magnet 301 and series relay C<3> in the same way as the corresponding relay in the first selector. The relapse of relay C<3> puts the rotary magnet 314 under control of relay F<3> and trunks are tested in pairs, relays F<3>, B<3> operating in the same way as relays F<2>, B<2>. Relay D<3> energizes in the same way as relay D<2>, but in addition to locking relay B' extends the c-wire and prepares a circuit over the a and b-wipers to associate relay E<3> with the vertical magnet at the third selector. Relay I<3>R<3> is not released. Third selector, Fig. 4. When relay D' extends the c-wire. relav D<4> energizes partially and pulls up its armature a to disconnect release magnet 440. The third digit operates relay I<3>R<3>, but relay E<3> is now associated with vertical magnet 400. The relapse of series relay C<4> energizes rotary magnet 404 under control of relay F<4> and hunting proceeds as in the preceding selectors, relays F<4>, B<4>, D<4> corresponding to relays F<2>, B<2>, D<2>. Relay D<4> on energizing grounds the test wiper of the selected set and extends the a and b-wires. Connector, Fig. 5. When the connector is seized, relay 544 energizes either directly from the wire 406 if connection is made over the even level shown in the upper part of Fig. 4, or in series with relay B<5> and test wire 436 if the connection is made over an odd level. Relay B if energized locks up and switches in the second wiper set. Relay B<5> is made slow to operate sc that a connection over its back contacts is not disturbed when the connector is being tested over an odd level and consequently a relay F<4> has tc energize in series with relay B<5>. Relay 544 energizes relay 545. Relay I<3>R<3>, Fig. 3, is now operated by the tens digit, but relay E<3> is now associated over the a and b wires with vertical magnet 505. Series relay C<5> falls back at the end of the digit and releases relay 545 (off normal springs 502 having changed over) which switches rotary magnet 504 into the stepping circuit. Relay C<5> re-energizes at the beginning of the units digit, and energizes relay 550 which locks up. Relay C<5> on falling back energizes relay 548 which connects ground to the b-wire over a front contact of slow relay 544 which it releases. This momentary ground energizes relay 303, Fig. 3, which locks up, disconnects relay E3, extends the talking wires and puts the upper winding of relay L<3>R<3> in series with its lower winding in place of the non-inductive winding of relay 303. Busy test and signal. If the line is busy, relav 545 is short-circuited by ground on the test wiper and the relapse of relay 544 sends back busy tone over 527, 530. Supply of ringing current and talking current. If the wanted line is idle, relay 545 energizes in series with the cut-off relay 552, locks up, shortoircuits its upper winding and releases relay 548 so that ringing current goes out from 521. The operation of ringing cut-off relay 553 extends the called loop backwards so that relay 360, Fig. 3, operates and reverses the current in the calling loop. Talking current is supplied to the calling loop over both windings of relay I<3>R<3> and to the called loop over relay 360. Release. Relapse of relay I<3>R<3> when the calling party hangs up releases relay T<3> which energizes release magnet 331 and ungrounds the cwire to release relays B<2> - - B<4> and D<2> - - D<4>. Release magnets 233, 440 operate. Relay D<4> also ungrounds the c-wire to the connector release relay 550, but until the called party hangs up, release of the connector is held up by relay 545 which remains energized over 520 called loop, 563, 517, 525. The release of relay 545 releases relay 553 and energizes release magnet 543.