Patent GB-426774-A (GB)
Title: Improvements in and relating to circuit arrangements for teleprinting exchange installations
IPC: H04L12/00
Filed: 1934-10-20
Abstract: 426,774. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. Oct. 20, 1934, No. 30115. Convention date, Oct. 20, 1933. [Class 40 (iii)] In a telegraph exchange installation in which the lines where they enter and leave the exchange terminate in repeating relays ER1, SU1, SR1, ER2, SU2, SR2, controlling supervisory relays R1, R2 which also act as calling relays, the release of a connection causes the repeating relays to reset in such a sequence that the occurrence of a fresh calling condition by the supervisory relay acting as a calling relay is prevented. In the system shown. a calling line TL1 is connected through a pre-selector VW1 exchange VA1, a two-way inter-exchange trunk FL, and exchange VA2 to the called line TL2. Each subscriber's line terminates at the exchange in a calling relay R1 and repeating relay ER1, the relay R1 serving also as a supervisory relay for controlling release. The inter-exchange trunk FL terminates in polarized relays SU1, SU2. Initiation of call. The depression of key ET, Fig. 2, short circuits condenser C to energize calling relay R1 over winding (i) thereby causing the pre-selector to find an idle first selector. The energization of the test relay T 1 reverses the current in relays SR1, L1 by connecting them to positive at the first selector, these relays connecting winding (ii) of the repeating relay ER1. across the calling line in place of relay R1. Establishment of connection. This is set up in the usual manner, the dialling impulses being repeated by relay ER1 over the a-lead to the first selector at exchange VA1 and subsequently by relays ER1, EU1, SU2, to the second exchange VA2. If the wanted line is idle, relay T2 reverses the current through relays L2, SR2, thereby placing repeating relay ER2 across the wanted line. Sub-station circuits. When the calling subscriber depresses key ET, relay E energizes relay U to start the tele-printer motor M and short circuit the condenser C. Similarly, at the called station, the current charging the condenser C energizes the relay E to start the motor &c. Transmission of telegraph signals. These are repeated in one direction by relays ER1, EU1, SU2, SR2 and in the other direction by relays ER2, EU2, SU1, SR1. Release. During a connection, the repeating relay ER1 is across the calling line, relay R1 having winding (i) connected to negative battery and its winding (ii) to the armature er1 of relay ER1, which during non-signalling periods is on its upper contact z. Momentary closure of its lower contact t during signalling is without effect on the slow-release relay R1, but an abnormally long interruption of the line circuit effected by the depression of the release key st, causes current in winding (ii) to neutralize winding (i) thereby de-energizing relay R1. The prolonged interruption of the circuit of relay ER1 also reverses the current in relays EU1, SU2, L2, SR2. Relay SU2 short-circuits a slow-release relay RU2 which causes slow-release relay F2 to energize relay EU2, thereby reversing the current in relay SU1. Owing to the delay caused by the slow-release relays RU2, F2, the reversal of current through the relays SR1, L1 by relay SU1 is prevented since the contact t12 has been restored to the position shown owing to the de-energization of relays R1, T1. The circuit of winding (ii) of relay ER1 is thus opened at contact r13 of relay R1 before it is closed at z by contact sr1 of relay SR1, thus preventing a false calling condition which would be set up if relay ER1 completed the circuit of the calling relay R1 over contact t of armature er1