Patent GB-256658-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1925-03-16
Abstract: 256,658. Standard Telephones & Cables, Ltd., (formerly Western Electric Co., Ltd.), (Deakin, G., and Polinkowsky, L.). March 16, 1925.. Automatic exchange systems.-Two-conductor trunk lines are disabled at their outgoing ends by manual means such as a key at the incoming end which removes the normal earth or battery connection from one of the conductors so that a selector which tests the trunk over this conductor will reject it if thus disabled. The selector will also pass over a trunk in which the talking conductors are open due to a fault. According' to one arrangement, Fig. 1. a separate test for disablement or faults is made immediately after the usual busy test, whilst in a second arrangement, Fig. 2, the two tests are made simultaneously. According to a further feature of the invention. a three-conductor trunk, Fig. 3, is disable at its outgoing end by means associated with the third conductor controlled for the incoming end. First arrangement, Fig. 1. When the sequence switch 15 moves into its 7th position, the lefthand and right-hand windings of the test relay 1 are connected in series over contact 11 to the test brush k, so that when a free trunk is found. relay 1 operates and causes the release of relay 2 which opens the driving circuit. The left-hand winding of relay 4 is now connected over contact 14 to the upper brush ! i and thence over the upper talking conductor of the seized trunk, and if the trunk is not faulty or disabled, relay 4 operates over earth at the incoming end and completes a circuit over contacts 19, 16 for driving the switch 15 out of its 7th position. If. however, the talking conductors are faulty or the trunk has been manually disabled by the removal of earth at the incoming end, relay 4 does not operate but a slow-operating relay 5 energizes over contacts 17, 18, 19 and short-circuits the test relay 1 which releases. Relay 2 re-energizes and hunting is resumed. The remaining operations of the selector shown in Fig. 1 are described in Specification 252,041. Second arrangement, Fig. 2. A relay 22 is connected as shown from the test terminal 30 to the lower talking conductor of the trunk so that when the trunk is seized the test relav 20 of the seizing selector energizes over a circuit including relay 22, the lower conductor and battery connected to contact 23. Relay 20 shunts its high. resistance left-hand winding to mark the trunk busy whilst relay 22 also operates and disconnects itself from the lower conductor. The resistanoe of the locking circuit of relay 22 is such that two test relays 20 are unable to remain energized in parallel, thus preventing double connections. The trunk is disabled by the disconnection of battery from contact 23 by manual means such as a key. Third arrangement, Fig. 3. The normal test circuit of the three-conductor trunk shown includes the right-hand winding only of relay 43. In order to disable the trunk, a plug is inserted in the jack 49 at the incoming end, thus completing a circuit over resistance 50 for relay 47, which removes a short-circuit from the left-hand winding of relay 43. The resistance of both windings of relay 43 is too great for a test relay 41 to energize in series therewith. Specification 184,249 is referred to.