Patent GB-191415471-A (GB)
Title: Improved Circuit Arrangements for Telephone Systems.
Filed: 1914-06-27
Granted: 1915-08-05
Abstract: 15,471. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. June 27. Automatic and semi - automatic exchange systems.-Relates to call-finder systems in which a calling line is sought for by all the finders that are idle at the moment, and in which when the calling line has been found by one of the finders, the other finders come to rest in the position in which they happen to be at the moment. Systems of this type have the defect that an idle finder may come to rest on a terminal of a line engaged in a connexion with a busy finder, and when this connexion is released, there are two idle finders on the terminals of the same line, and in response to the next call these finders may hunt in unison and cause the setting up of double connexions. To avoid this, the present invention provides means for preventing an idle finder from remaining on the terminals of a line occupied by a busy finder. In the arrangement shown in Fig. 1, the fourth wiper of a finder AS1 serves to connect ground through a resistance w1 to a circuit including a relay HR individual to the line on which the finder is resting. The current over the resistance w1 is insufficient to energize the relay HR; but if a second finder ASn should come to rest on the same line, connecting a second resistance Wn in parallel with the resistance w1, the relay HR responds and energizes the starting-relay AR, which sets all the idle finders moving until none of them are on the same lines as busy finders. This arrangement may be modified so that the idle finders are only moved on when the busy finder becomes idle. In the arrangement shown in Fig. 3, not all the idle finders are moved on, but only those which come to rest on lines already occupied by busy finders. If, at the moment when the starting-relay AR is deenrgized, an idle finder AS1 should be on the terminals of a line already occupied by a busy finder ASn, a circuit is closed through the relay V and rotary magnet D of the idle finder, contact 18 (the slow-acting relay V not having yet had time to de-energize), multiple circuit d of the fourth set of terminals of the line on which the finders are resting, contact 27 of the de-energized relay V of the busy finder, and an interrupter, and the idle finder AS1 is thus moved forward to the next set of terminals. A key Ta is provided by which an attendant can energize the relay V to complete the abovementioned circuit. In the arrangement shown in Fig. 4, the call-finders have only the customary three wipers, the objects of the invention being secured without employing a separate test circuit. When the subscriber T1 makes a call, the line relay R is energized by its winding I and energizes a relay U, which closes a contact 23. If any idle call-finder should be at rest on the calling line, the contact 23 at once closes a circuit through its test relay P; but otherwise a starting-relay AR is energized and completes the circuits of the stepping-magnets D1 of all the idle finders. When a finder AS reaches the calling line, a circuit is closed through both windings of the test relay P, the winding II of the line relay R, and the cut-off relay T. The relay P locks itself through its low-resistance winding II to mark the calling line non-selectable to other switches, while the relay T disconnects the meter Z, the relay U, and the winding I of the relay R. At the contact 33, a relay E is energized which brings into circuit the stepping-magnet D2 of the preliminary selector VW associated with the finder AS, and when the switch VW has found an idle outgoing line, a relay P1 is energized, which thereafter controls the incoming test circuit at the contact 42. If now an idle call-finder comes to rest on the terminals of the line T1, a circuit is closed through contacts 42, 32, the winding II of the test relay of the busy finder, the test wire 45, both windings of the test relay of the idle finder, and the common starting-relay AR. The test relay of the idle finder is not energized in this circuit, but the relay AR responds and causes all the idle finders to move on until none of them are on the same lines as busy finders. To secure that an idle finder shall not be shifted if it comes to rest on a line occupied by a connector, each subscriber's line is provided with separate test wires 45, 48 for the call-finders AS and connectors LW respectively. When the subscriber T1 is the calling subscriber, the relay R is first energized by the line winding I and is maintained energized during conversation by the winding II, this winding being energized in the test circuit in series with the cut-off relay T. The test wires 45, 48 are thus connected at the contact 21, so that the line T1 is rendered non- selectable to connectors as well as call-finders. On the other hand, when the subscriber T1 is the called subscriber, the relay R does not become energized at all, because its second winding is normally short-circuited bv its own back contact 22. In this case, therefore, the test wires 48, 45 remain disconnected, and a moving- on potential is not applied to the test wire 45. A modification of the arrangement shown in Fig. 4 is described, by which a call-finder, which becomes disengaged at a moment when a calling line is being searched for, is prevented from joining in the general hunting movement of the idle finders as long as the terminals of the line on which it is standing are being swept by any of the other finders.