GB501705A - Telegraph exchange system - Google Patents

Abstract

501,705. Telegraph exchange systems. LORENZ AKT.-GES., C. May 19, 1938, No. 14979. Convention date, May 19, 1937. [Class 40 (iii)] A selecting dial is locked until a first group selector is engaged, and is released from the automatic exchange, Fig. 2, by an increase of the current in the subscriber's line a, b. When a ringing key AT, Fig. 1, is pressed, the first stage of a two-stage relay W responds and bridges the calling key, and a relay E, Fig. 2, connects a relay R to the current supply. This connects the rotary magnet D of the preselector, and, when a free bank of contacts is found by the brushes a1 .. d, a relay T is energized. A resistance w3 is thus bridged to increase the current in the subscribers' line. This completes the energizing of the relay W, which releases the dial and connects a busy lamp L to the mains Ne to indicate that selection can begin. The relay T also disconnects the rotary magnet and applies reversed current to relays S, L, which reverse the current in the subscribers' line. A polarised relay P responds and connects a magnet H to the mains to connect the motor M of the printing telegraph machine to the mains and a transmitting contact SK and receiving magnet EM to the subscriber's circuit. The relay W drops and locks the dial to prevent interference with the communication' by dialling. At the end of communication, pressing a key ST interrupts the subscriber's loop.