Patent GB-191001421-A (GB)
Title: Improvements in or relating to Telephone Systems.
Inventor: KEITH ALEXANDER ELSWORTH
Filed: 1910-01-19
Granted: 1911-04-19
Abstract: 1421. Keith, A. E. Jan. 19. Automatic exchange telephone systems.-In systems of the kind in which a calling subscriber is connected automatically with an id!e first selector, a large number of first selectors is allotted to several groups of subscribers and a calling-line is connected to an idle selector through two intermediate non- numerical switches, of the type described in Specification 26,301/06. By this means the total number of first selectors in an exchange is reduced, since the maximum percentage. of simultaneous conversations is less in a large group of subscribers than in a small group. The invention is described as applied to a system in which the switches are operated over a metallic line-circuit, slow-release relays serving to make the necessary changes in the connexions during the pause between each set of selecting-impulses. In the system described, each subscriber's line terminates in an individual switch C, Fig. 1, 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 a disengaged trunk leading to an idle intermediate switch C<1>, in the same general manner as is described in Specification 26,301/06. The intermediate switches C<1> are of the same character as the switches C, a group of such switches being controlled by the master switch D<1>. Subscriber's individual switch. The construction of the combined line switch and relay 39 is identical with that described in Specification 1298/10. The construction of the master switch is fully described and is substantially identical with that described in Specification 1419/10, except that an additional row of contacts a<1>, wiper 56, and relays 141<a>, is provided for a purpose which will be explained later. When a calling subscriber A removes his receiver, current flows from the battery lead 100 through a contact 98, 97, winding 50, contact 96-95, line 33, sub-station apparatus, line 34, contact 94-93 to ground G<1>. The attraction of the armature 52 closes a circuit from the battery lead 100 through the windings 51, 48, and contact 93-101 to earth. The attraction of the armature 53 disconnects the winding 50 from the line-wires, and the movement of the plunger arm 38 not only forces the springs 40, 42, 44, 46 into contact with the terminals 41, 43, 45, 47 of an idle intermediate switch C', but also closes a contact 103-104, which short-circuits the windings 51. The armature 52 releases slowly to open the circuit of the pull-down winding 48, but before this happens a circuit is completed through a hold-on winding 49, which is powerful enough to maintain the plunger arm attracted, although not to pull it down initially. The circuit through the wiuding 49 is completed when the lead 126<a> is earthed as explained in the following paragraph. The earthing of the lead 126<a> also completes a circuit from the battery lead 100 through the relay 141 of the master switch D, contact 143, wiper 57, contact 142 individual to the switch C', and lead 126<a> to earth. The relay 141 closes the circuit of a relay 144, which in turn completes a circuit through a relay 146 and the motor magnet 54 of the master switch. The relay 146 disconnects the windings 50 of all the line switches from the battery lead, and connects them to a busy generator I', while the master switch is in motion. The master switch continues to rotate the plungers until the wiper 57 engages an ungrounded contact, exact alinement of all the idle plungers with the selected terminals being ensured by the cam device 59, 60, as described in Specification 1419/10. Intermediate switch. When the contact 44-45 of the switch C is closed, current flows from the battery lead 100 through a contact 110-109 of the master-switch relay 152, relay 108, contact 107-106, magnet 61, and contact 45-44 to earth. The magnet 61 attracts its plunger arm so as to bring the contacts 115, 117, 119 into contact with the terminals 116, 118, 120 of an idle first selector, and at the same time, by attracting its relay armature 114, completes a locking-circuit for itself through the contact 106-107<a>, and resistance 123. The relay 108, which is only energized momentarily, closes the circuit of a slow-release relay 63, which earths the lead 126<a> until a fresh earth connexion is established at the first selector, thus closing the circuit of the winding 49 of the switch C, as previously described. The closing of the contact 121-122 completes a circuit through a relay 151 which controls the master switch D' in the same way in which the relay 141 controls the switch D. While the switch D' is in motion, the armature 110 opens the circuit of a relay 62, the back contact of which is connected to one of the contacts a<1> of the switch D, and by controlling a relay 141<a> prevents the switch D from coming to rest with its plungers above the contacts of an intermediate switch belonging to a group, the master switch of which is in motion. First selector. The closure of the contacts 115- 116, 117-118 of the switch C<1> completes the circuit of the line relay 70 of the first selector. The relay 70, Fig. 2, closes the circuit of a slow-release relay 78, which by closing contact 138-139 earths the leads 126, 126<a>, 140, thus maintaining a guarding potential on the test contacts 120, 47 and test lead 140, and also establishing a new circuit for the winding 49 of the switch C. The first set of selecting-impulses, sent by interrupting the line circuit, are repeated by the relay 70 over a circuit from ground through the contacts 132-133,136-137, private-magnet relay 79, vertical magnet 67 and side-switch arm 72 to the battery lead. The magnet 67 raises the wipers 64, 65, 66 to the row of terminals of second selectors of the required thousands group. The slow-release relay 79 is energized by the first impulse and closes a circuit for the private magnet 73, which is de-energized, so as to move the side-switch into its second position, when the relay 79 is no longer energized by the selecting-impulses. In the second position of the side-switch arm 72, the battery lead is connected through a slow-release relay 80 to the rotary magnet 68, which steps round the selector until its wipers find an idle second selector. This hunting movement is controlled by the private magnet 73 in the usual way, the magnet being deenergized when an unearthed test contact is found, so as to move the side-switch into its third position. In order to render the chosen second selector busy to other selectors before the relay 165 has time to respond, the test wiper 65 is earthed momentarily over the arm 71 and the contact 160-159 of the slow-release relay 80 in series with the rotary magnet. When the arms 69, 69<a> move into their third position, the relay 70 is de-energized, but the circuit of the slow-release relay 78 (which functions as a release relay) is maintained over the contact 170-160 of the relay 80 (which must consequently be quicker than the relay 78), arm 71, test wiper 65 to earth at G<12> in the second selector. Second selector. The movement of the sideswitch arms 69, 69<a> into their third position closes a line circuit through a relay 162, which completes the circuit of the release relay 165 in the same way in which the relay 70 controlled the relay 78. The relay 165 closes contact 167-168 so as to connect the test wiper 65 to the arm 166, which is directly earthed in the first and second positions of the side-switch and in the third position is connected over a contact 179-180 and arm 178 to the test wiper 177, which is earthed at the connector H, Fig. 3. The second selector now responds to the second set of selecting- impulses in the same way as the selector E, and extends the connexion over the trunk 171, 172 to an idle connector. The release relay 165 is then connected to earth at the connector over the circuit referred to above. Connector.' When the side-switch of the second selector moves into its third position, the line relay 81, Fig. 3, is energized and completes the circuit of a slow-release relay 87 which closes contact 175-176 so as to maintain the circuits of the release-relays 78, 165 of the first and second selectors. The third set of selecting-impulses is repeated by the relay 81 over a circuit which extends from ground over contacts 182-183, 184-185, vertical magnet 82, arm 186, and a slow-release private-magnet relay 86 to the battery lead. The magnet 82 raises the connector wipers to the desired horizontal row. The relay 86 controls the private magnet 85 as in the first selector. In the second position of the sideswitch, the final set of selecting-impulses is repeated by the relay 81 to the private-magnet relay 86 and the rotary magnet 83, which moves the wipers to the contacts of the desired line. Busy test. If the required line is engaged, its test contact is earthed, so that, when the privatemagnet relay 86 de-energizes, the circuit of the private magnet 85 is still closed over the contact 188-216, arm 192, contact 207-206, winding 229 of the relay 89, and contact 197-198 of a relay 88, to the earthed test wiper 199. The private magnet thus remains energized, locking the side-switch in its second position, and at the same time the relay 89 completes a circuit through the locking relay 88, which (1) disconnects the rotary magnet 83 from the impulse spring 183, (2) shifts the holding- ground of the magnet 85 and relay 89 from the test lead to ground G<19>, and (3) connects the busy transformer I to the calling-line. The connexion is released when the calling subscriber replaces his receiver as described later. Supply of ringing-current. If the required line is disengaged, the side-switch moves into its third position in which (1) the arm 195 earths the test wiper 199, thereby energizing the cut-off winding 196 of the called subscriber's individual switch C<2>, whereby the relay armat