Patent GB-555396-A (GB)
Title: Improvements in telephone systems
IPC: H01H50/72
Filed: 1942-07-11
Abstract: 555,396. Telephone systems ; electric switches. WESTERN ELECTRIC CO., Inc. July 11, 1942, No. 9672. Convention date, July 19, 1941. [Class 40 (iv)] [Also in Group XXXVII] A single relay operates in a self-interrupting circuit to generate intermittent ringing current, and energizes steadily on the reply of the called party to cut off the ringing current and complete the talking circuit. The relay is of the kind described in Specification 543,008, [Group XXXVII], in which two parallel pole-pieces have openings for receiving switch elements of the magnetically-operated mercury type. In the switch elements shown in Figs. 6, 7, a tubular armature 15 having its lower end immersed in mercury within an envelope 10 carries a pair of parallel wires 17 which conduct the mercury upwardly by capillary action and terminate in a contact member 18 for cooperation with back and front contacts 19, 20. In Fig. 7, the armature 15 is open at its lower end and a restraint is imposed on its upward and downward movements by the surface tension of the mercury film between the movable contact 18 and the fixed contacts 19, 20, so that either movement may be made fast or slow by giving the contacts suitable areas. In Fig. 6, in addition to the contacts being of large area to increase the surface tension effect, the armature 15 is closed at its lower end except for a small opening 21 through which the mercury flows to give a dashpot effect. When the relay is energized by impulses at the rate of 20 per second, the armature rises in a stepby-step manner and closes its front contact after one second, and if the relay is then deenergized, a period of 3 seconds elapses before the back contact is again closed. Circuits. Relay 4 which may be included in a cord-circuit or a final selector energizes when the sleeve or test wire of the called line is grounded and immediately interrupts its circuit at contact 22. It holds however in series with the subscriber's bell 28 and condenser 29 until the latter is charged, and then remakes contact 22 over which the condenser discharges. This action is repeated, and the bell thus receives ringing current at a frequency of 20 cycles. The relay circuit also includes contact 23 of the kind shown in Fig. 6 which periodically interrupts the action to give a ringing period of one second and a silent period of 3 seconds. When the subscriber replies, the relay energizes steadily over the line and at slow-operating contacts 24, 25 completes the talking circuit and a supervisory circuit. In the modification of Fig. 2, relay 4 energizes first over the calling line and contact 30 which is fast-to-operate and slow-to-release, after which the action is the same. In Fig. 3, two relays 4A, 4B are used for interconnecting two stations. One of the relays energizes steadily over the calling line and makes at contact 30A or 30B the self-interrupting circuit for the other relay, which as before energizes steadily upon reply. The modification of Fig. 4 employs a single relay 4 and a pair of selecting relays 31A, 31B, one of which energizes over the calling line and connects up relay 4 to apply ringing current to the called line. Relays 31A, 31B may be of the same kind as relay 4 or of ordinary type.