Patent GB-191402543-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1914-01-30
Granted: 1915-02-01
Abstract: 2543. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Jan. 30. Automatic and semi-automatic exchange systems.- Relates to systems in which an established connexion between two subscribers on an automatic exchange may be broken in upon by an operator in case one of the subscribers is wanted for a preferred call, such as a long distance call. A discriminating busy potential is applied to the test terminals of a called line by a relay in the circuit of the connector which completes the call, this relay being energized over the incoming test circuit when the call is made by an operator, but not when the call is made by a subscriber on the automatic exchange. In the arrangement shown in Fig. 1, an operator at a manual board M (which may represent a manual section of the automatic exchange or may be at a separate exchange), completes a connexion from a subscriber T to an automatic subscriber A by plugging a cord into a jack J<3> and operating her impulse-transmitter to control the selectors I, F and a connector H. The selectors I are special to the operators M, but the switches F, H are the same as are used by the automatic subscribers themselves in setting up connexions. If the wanted subscriber's line is already engaged, the operator receives a busy signal which indicates by its character the nature of the existing connexion, the signal being of one sort if the existing connexion has also been set up by an operator, of a second sort if it has been set up by the wanted subscriber, and of a third sort if it has been set up by another automatic subscriber. In either of the two lastmentioned cases, the operator plugs into a jack J<4> leading direct to a connector N of special character associated with the group of lines to which the wanted subscriber belongs. The connector N is modified so as to be able to complete a connexion with the wanted line in spite of the busy potential on its test terminals, and the opera'or is thus enabled to inform the wanted subscriber of the call which awaits him. When the existing connexion has been released, the waiting call may be completed through the connector N or may be set up again through the switches I, F, H. In a second arrangement, which avoids the necessity for either the discriminating busy signals or the special connectors N, the ordinary connectors H of the automatic exchange are modified so that, when they are under the control of an operator M, they are capable of completing a connexion with a wanted line even when that line is already in talking connexion with another line of the automatic exchange. Specifications 26,301/06 and 1419/10 are referred to. The circuits for establishing a connexion between two automatic subscribers A, Fig. 1, are shown in Figs. 2 and 3. Group selectors E,F, Fig. 2. When the subscriber A lifts down his receiver, his line switch C connects him in known manner to an idle selector E, energizing the relays 35, 39. The interruptions of the line-current representing the first digit are repeated by the relay 35 as impulses to the vertical magnet 33, which raises the wipers 30, 31,32 to the desired level. A slow-release relay 40 in the circuit of the vertical magnet is energized by the first impulse and closes the circuit of a relay 95, which locks itself up in a circuit including an off-normal contact 37 and a contact 96 controlled by the rotary magnet 34. After the last impulse, the relay 40 de-energizes and completes the self-interrupting circuit of the rotary magnet 34, which rotates the wipers in search of an idle second selector. As long as the wipers are on the terminals of a busy trunk, the locking-circuit of the relay 95 is maintained through the test wiper 32 in spite of the opening of the contact 96 of the rotary magnet 34 ; but as soon as the wipers arrive on the terminals of an idle trunk, the relay 95 is unlocked, and the de-energization of this relay cuts out the rotary magnet and energizes the switching-relay 101, which extends the line connexion through the wipers 30, 31 to the relay 103 of the second selector F. The relays 35, 39 are now de-energized, but a holding-circuit for the relay 101 is provide i by the relay 104 of the second selector. This selector operates in response to the second series of impulses in the same way as the selector E to extend the connexion to the connector H, Fig. 3. Connector H, Fig. 3. In response to the third and fourth sets of impulses, the connector operates in known manner to select, test, and ring the wanted line. If this line should be found to be engaged, the side switch is locked in its second position, and a busy signal is sent back to the calling line through the test wiper 43, as described later. Metering. The meter 28, Fig. 2, is operated in the usual way by the reversal of the current in the calling line when the called subscriber replies. Operators' circuits, Fig. 4. When the subscriber T operates his magneto 58, the line relay 6- becomes energized and locks up and lights the call lamp 62. The operator inserts the plug P' in the jack J, energizing the cut-off relay 61, which deenergizes the relay 60 and lamp 62 and energizes the busy indicators 63 associated with the multiple jacks J<1>. If the wanted subscriber belongs to the automatic exchange, the operator plugs into a jack J<2> leading to a selector I. Fig. 1. Relays 141, 69 in the sleeve-circuit are energized, and the relay 69 energizes the engaged indicators 70. (The relay 68 in the same circuit is for the purpose of adapting the cord circuit M for common battery manual lines and is not energized in series with the relay 69.) The selector I is the same except in one respect mentioned below, as the selector E, Fig. 2, and the second selector and connector through which the connexion is completei are the same as the switches shown in Figs. 2 and 3. To control the selectors, the operator's impulse-sender 140 is bridged across the outgoing line by the key K<1>. Having completed the connexion, the operator restores the key K<1> and throws the key K<2> to connect her listening-set across the line to listen for a busy signal. The restoration of the key K<2> bridges the polarized relay 67 across the line, and when the called subscriber answers, this relay responds, owing to the reversal of the line-current by the relay 52, Fig. 3, and extinguishes the lamp 66. When conversation is finished, the calling subscriber rings off by means of his magneto 58, energizing the relay 182, which removes a short circuit from a self-locking relay 183, which prepares the circuit of the supervisory lamp 65, which lights up when the relay 182 deenergizes again. The called subscriber hangs up his receiver, causing the line-current to be again reversed, so that the polarized relay 67 lights the supervisory lamp 66. The automatic part of the connexion is released when the operator withdraws the plug P<2>. Busy signals. The test terminals of a busy automatic subscriber are connected to ground through the secondary of a busy tone device Q, Fig. 2, or Q<1> or Q<2>, Fig. 3, depending on whether he is a calling subscriber, a called subscriber in a local call, or a called subscriber in a long-distance call established by an operator. The connexion of the tone device with the test terminals is made in the first case by a contact 24, Fig. 2, of the line switch C, and in the second and third cases by the back and front contacts of a relay 53, Fig. 3, in the incoming test lead 109. The relays 101, 111 of the selectors E, F are of too high resistance to allow the relay 53 to become energized in series with them, but the corresponding relay of the operatorcontrolled selector I, Fig. 1, is of lower resistance and allows the relay 53 to energize. When a connector H, Fig. 3, endeavours to make connexion with a busy line, its side switch is locked as usual in the second position by the energization of the private magnet 50 in series with the relay 152, and a busy tone current indicating the nature of the existing connexion is sent back to the calling subscriber or operator through the test wiper 43 and the contacts 156, 157 of the relay 152. Alternative busy signal circuits. In the modified connector shown in Fig. 7, ground is connected to the test terminals of a seized line either through a resistance 194 or directly, accordingly as the relay 191 is energized or not. The relay 191 corresponds to the relay 53, Fig. 3, and is only energized when the connector is under the control of an operator, i.e. when the call is a long - distance one. If a second connector attempts to make connexion with the same line, its side switch is locked in its second position by the energization of the private magnet 211 in a circuit including the relay 198 and the lower winding of a relay 190. The current in this circuit is only sufficient to energize the relay 190 if the tested terminal is directly grounded, i.e. if the existing connexion was a local one. The relay 190, in energizing, opens a short circuit across its upper winding, which is included in the locking-circuit which the relay 198 closes through the magnet 211. Thus the relay 190 of a connector attempting connexion with a busy line is energized if the existing connexion is a local one, but not if it is a long-distance one, and the connexion of the busy tone device Q<3> or Q<4> to the calling line is determined accordingly. In this modification, the line switch of a calling subscriber is arranged to ground his test terminals directly, instead of through the secondary of a busy signalling device, as shown in Fig. 2. Operator's connector N, Fig. 6, for breaking-in on busy lines. When this connector is set on the terminals of a busy line, the relay 162 is energized (over the side-switch arm 161 in its second position and the test wiper 160) and locks the private magnet 170 in series with a breaking-in relay 166, which completes the talking connexion. The operator then requests the wanted subscriber to