Patent GB-168597-A (GB)
Abstract: 168,597. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Lomax, C. E.). Sept. 3, 1920, [Convention date]. Automatic and semi-automatic exchange systems.-An automatic switch when taken into use directly by a subscriber, responds to the first digit dialled, and according to the value of this digit, operates as a group selector to select an idle one of a group of lines in a certain level, or it functions as a connector, and responding to subsequent digits, establishes connection with a wanted subscriber. It may also be taken into use by another switch acting as a selector, in which case it is immediately caused to operate as a connector. The invention is described as applied to a private branch exchange of 200 subscribers, divided into two 100-line units, that shown on the left of Fig. 2 serving lines numbered 301 to 399, and that on the right of the figure serving lines numbered 401 to 499. These units are henceforward referred to as the 300 unit and the 400 unit respectively. Each subscriber is allotted a line switch C adapted to engage one of a group of combination selector connectors D serving each unit. The selector connectors D are of the Strowger type, but have two sets of wipers and two sets of banks, an upper set of selector banks SEL, and a lower set of connector bands CON, in which latter terminate the subscribers' lines of the particular unit served by the switch. The selector connectors normally operate as selectors, and are raised to a level determined by the first digit, to engage an idle trunk leading to an operator's position O, to a main exchange through repeaters REP, or to a selector connector of the other unit. If, however, the wanted subscriber is in the same unit, the selector connector is raised to a critical level (the third in the 300 unit and the fourth in the 400 unit) at which shaft springs are closed, which cause the switch to release, and change its character to that of a connector. The operation in fuller detail is described below with reference to Fig. 1. Connection with a subscriber in the same unit. Assuming that a subscriber A in the 300 unit desires connection with a subscriber A<1>, on removing his receiver the subscriber A is connected bv his line switch C to an idle selector connector D, the line relay 51 and release relay 52 of which are energized in the the usual manner. The relay 52 connects ground to the release conductor 28 and to the release conductor 202 leading to the selector connectors of the other unit, and prepares a circuit for the vertical magnet 60, which is energized by the first dialling impulses to step up both sets of wipers 101, 102, 103 and 104, 105, 106 to the third and critical level. In this position the shaft-controlled spring 41 breaks contact at spring 40 and engages the contact 42, thereby (1) disconnecting the rotary magnet 61, the circuit of which was prepared at armature 76 of the stepping relay 50 (locked over the off-normal contacts 97, 98 energized on the first movement of the shaft), and (2) completing a circuit for the release magnet 62, which restores the wipers, and at its armature 27 energizes the relay 59. The relay 59 locks up over the armature 94, disconnects the selector test wiper 102, connects up the connector test wiper 105, and breaks the circuit of the release magnet 62 at armature 95. The switch D now functions as a connector, and on the calling subscriber dialling the second digit the vertical magnet 60 raises both wiper sets to the corresponding level. If this be the third level, the closure of contacts 41, 42 has no effect since the circuit of the release magnet 62 is broken at armature 95. On the relapse of the series relay 53 the operating circuit is transferred to the rotary magnet 61, which on the subscriber dialling the last digit, energizes in series with the slow-release relay 57, and rotates the wipers 104, 105, 106 on to the contacts of the wanted line. The relay 57 connects the test wiper 105 to the upper winding of the combined test and back-bridge relay 55, which, if the wanted line is busy, is energized and locked up over its armature 78, and the calling subscriber given a busy signal from the machine Q over the armature 80. If the wanted line is idle, on the relapse of relay 57, the switching relay 58 is energized over its lower winding, in series with the switching relay 16 of the switch C<1> individual to the called subscriber A<1>. The relay 16 only operates half way, so that the line conductors are not connected through to the switch C<1>. The switching relay 58 locks up over its upper winding and ringing current is intermittently sent overthe called ine in the usual manner. When the called subscriber answers, the ringing cut-off relay 56 is energized and completes the talking circuit over the armatures 81, 83. Release is effected in well-known manner when the calling subscriber hangs up. Connection with a subscriber in the other unit. Assuming a subscriber in the 300 unit desires connection with a subscriber in the 400 unit, on. dialling the first digit (four), the selector connector D taken into use will be raised to its fourth level as previously described. On the relapse of the series relay 53, however, a circuit is completed for the rotary magnet 61 over the contacts. 40, 41, and ;he armature 76 of the stepping relay 54 (which is locked energized over the off-normal springs 97, 98). The rotary magnet steps the wipers on to the first set of bank contacts, and breaks the circuit of the stepping relay 54 which in turn disconnects the rotary magnet. If the first trunk is busy the relay 54 is again energized and the operation is repeated, the wipers being stepped round until an idle trunk is found, when a short-circuit is removed from the switching relay 50, which extends the line to an idle selector connector in the 400 unit. This switch is similar to the switch D, the inter-unit trunks being represented by the conductors 201, 202, 203, and for the purposes of this abridgment the circuits of the 400 unit switch will be followed on Fig. 1. When the trunks 201, 202, 203 lending to the 400 unit selector connector are seized bv the 300 unit selector connector, ground is placed on the release conductor 202, and a circuit is completed over the nornally closed contacts of armature 75 for the relay 59 of the 400 unit selector connector, the character of which is now changed to that of a connector, as previously described. The line and release relays are energized over the extended line circuit, and on the last two digits being dialled, the 400 unit selector connector operates to establish connection with the wanted line, in the same manner as has been described in the previous paragraph with reference to the switch D. Connection with an operator's position or the main exchange. Trunks from the operator's positions terminate in the first seelctor levels and those from the main exchange apparatus in the second selector levels. The wiper sets of an idle selector connector are raised to their first or second levels by the sending of one or two dialling impulses, and the selector connector, functioning normally as a selector, engages an idle trunk.