Patent GB-191219253-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-08-22
Granted: 1913-09-22
Abstract: 19,253. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Aug. 22. Automatic exchange systems.-In order to prevent the possible energizing of the line relay of a wanted subscriber, due to this relay not having been fully disconnected by the cut-off relay before the application of ringing-current, the connexion between the calling and called lines is not completed until a predetermined interval after the line relay has been disconnected from the called line. This is effected by a slow-release relay which is connected in parallel with the private magnet. This arrangement permits the subscriber's lines to be connected to the connector bank terminals directly, instead of through the contacts of the subscriber's cut-off relay. Operation of system. The invention is described as applied to a two-wire system of the kind described in Specification 1419/10, in which a calling subscriber A is connected through a line-switch C, group selector E, and a connector H to the wanted subscriber. Reference is also made to Specifications 26,301/06, 1298/10, and 29,654/10. Line switch. The line switch C, Fig. 1, is similar to that described in Specification 1419/10, except that the line relay 39 is structurally separate from the operating-magnet 120, which operates the cut-off armature 106. When the calling subscriber removes his receiver, his line relay 39, which is of the slow-release type, is energized over the cut-off springs, and completes the circuit of the pull down winding 40, thus extending the line to an idle group reflector E. Group selectors. The first two sets of impulses sent by the calling subscriber operate the group selectors such as E, in the manner described in Specification 1419/10, so as to extend the calling line to an idle connector H serving the wanted line. Connector. The line relay 16, Fig. 2, is now energized over the springs of the back-bridge reversing-relay 18, and energizes the release relay 26, which maintains a holding-ground on the test lead 91 for the selector release relays. The third set of selecting-impulses is repeated by the relay 16 to the vertical magnet 14 through the slow-release relay 27, which, as soon as the impulses cease, de-energizes the private magnet 25, thus moving the side-switch into its second position. The final set of impulses is repeated by the relay 16 to the rotary magnet 15, which brings the wipers to the contacts of the desired line. Busy tests. The test terminals of busy lines are earthed, so that when the slow-release relay 27 de-energizes after the rotary movement of the connector, the private magnet 25 will energize, if the wanted line is busy, in series with a relay 100, thereby locking the side-switch in its second position. The relay 100 locks up and connects a busy generator S to the calling line. Release is effected when the calling subscriber hangs up. Ringing-current. If the wanted line is idle, the side-switch passes into its third position, and the arm 24 completes a circuit through the ringing-relay 29 and interrupter. Connexion with the wanted line is, however, interrupted at the contacts of a slow-release relay 28, which was energized in parallel with the private magnet 25, so as to give time for the cut-off armature 75 to disconnect the line relay 125 before the application of ringing-current. As soon as the relay 28 de-energizes, the ringing- generator M is connected to the called line. When the ringing-relay is first de-energized after the called subscriber has replied, the backbridge relay 18 is energized, its right-hand winding being earthed over the contact 80 of the relay 26. The relay 18 is thus under the control of the calling subscriber for reasons described later in connexion with release. The relav 18 reverses the connexions of the line relay 16 with the calling line, the consequent reversal of current serving to operate the subscriber's meter or an operator's supervisory signal in known manner. The relay 18 also energizes a relay 87, which locks up and cuts off the ringing-relay 29. Release. When the calling subscriber replaces his receiver, the line-relay 16 de-energizes the release relay 26, which completes the circuit of the release magnet 17 and also removes the holding ground over the test lead 91 for the release relay 48, Fig. 1, which in turn releases the selector E. The de-energizing of the relay 48 removes current from the holding-winding 49 so that the line switch C is also released. It has been previously pointed out that the circuit of the back-bridge relay 18, Fig. 2, includes a contact 80 of the release relay 26, so that it is under the control of the calling subscriber. This has no particular function in the system shown, but is of value in small exchanges having no group selectors, the circuit of the holding-winding 49 being then directly controlled by the relay 26. If, in such a system, the back-bridge relay 18 is controlled entirely by the called subscriber, it might happen that the holding-winding 49 might release the cutoff armature 106 before the plunger arm was fully withdrawn. Under these circumstances, a fresh circuit for the line relay 16, Fig. 2, would be completed through its upper winding, contact 112 of relay 18, trunk 59, to ground G<7>, and the relay 16 would again energize the relay 26, which in turn would earth the holding-winding 49 of the line switch C. The circuit of the relay 16 would again be broken, and the cycle of operations would be repeated again and again until the called subscriber hung up. In the arrangement shown in Fig. 2, this is prevented by the fact that the back-bridge relay 18 is deenergized when the calling subscriber hangs up, and, by reversing the battery connexions to the relay 16, prevents the energizing of the latter if the trunk 59 is grounded before the line switch is fully released.