Patent GB-371376-A (GB)
Title: Circuit arrangement for telegraphic installations
IPC: H04L12/00
Filed: 1931-01-20
Abstract: 371,376. Telegraph exchange systems. LORENZ AKT.-GES., C., 1, Lorenzweg, Tempelhof, Berlin. Jan. 20, 1931, No. 1956. Convention date, Jan. 23, 1930. [Class 40 (iii).] In a telegraph exchange in which the connection is automatically released when signalling has ceased for a given time, means are provided for holding the receiver relay at the subscriber's station during calling and clearing. Idle state. In the line and at the subscribers' stations such as Tn current is normally flowing but is kept small by the resistance Wi5. The receiver relay EM and (at the exchange) the line relay R are normally energized. Seizing a call-finder. Subscriber Tn seizes a call-finder AS by momentarily breaking circuit at E. Line relay R releases and cuts in relay An, which at 4an cuts in relay C which at 6c locks out other call finders (associated with further relays C arranged in a relay chain) and at 7c cuts in the switching magnet D and interrupter Un. Magnet D steps the call-finder AS until arm a finds the calling station, for which battery-positive is accessible through 1r. Cut-off relay T and relay Q then pull up, line relay R being thus cut off at 1t but earthed at 14t so that it re-energizes. At the same time the impulse relay I is, at 15q, 16q, brought into circuit with the line a, b ; it pulls up on potential derived through Wi3 and cuts in the slowrelease relay V at 8i, the switch-magnet D in this circuit being unaffected owing to the high resistance of relay V. Relay C is cut off at contact 15v. The ammeter M at station Tn indicates that the circuits are ready for dialling. Operation of line selector. To select sub. scriber Tn1, subscriber Tn dials by means of contact i, the arrangement shown allowing of only single-digit calls. When the dial switch is off normal, contact k is earthed and contact k2 is closed by that switch. The receiver magnet EM is therefore held energized, during dialling, by an earth-return circuit through switch-arms a, d1 and resistance Wi3; whereas the dialled impulses (interruptions) pass via contact k2, dialling contact i, switch-arm band impulse relay I. Impulse relay I is thus operated the required number of times, slowrelease relay V meanwhile holding on. Contact 19i operates the stepping magnet D1 and sets line-selector LW to the position for station Tn1. Testing called line. Slow-release relay U pulls up during dialling but is short-circuited at 8i thereafter. Meanwhile at 26u it cuts in the testing relay P, which pulls up if it has not already been marked busy by the short-circuiting at 21p of its winding I. Transmission of messages. The message circuit runs as follows : earth, battery, Wi3, switch-arm d1, 11v, switch-arm a, station Tn, switch-arm b, 12v, I, 12q, 25u, 8p, switch-arm a1, station Tn1, switch-arm b1, 9p, earth. Relays R, T, V, P are energized and relays U, Q de-energized. When the call signal was sent from Tn, receiver magnet EM was momentarily released and its armature m cut in the motor Mo. This armature does not break contact until signals have ceased for 30 seconds, so that the motor runs throughout signalling. The motor closes centrifugally a contact x which short-circuits the high resistance Wi5. When contact 12q is interrupted, the receiver magnet EM1 at Tnl releases and starts the motor Mol in a similar manner. The ammeter M1 indicates that the circuit is through. Clearing. The connection is released when contact O is opened automatically by the prolonged cessation of signals. Magnet I releases and short-circuits V at 8i. Relay U is then cut off at 17v, and relay P at 13v. The stepping circuit is closed at 10p for magnet D1 which steps the switch home under the control of interrupter Un. The call-finder As rests in any position and is not stepped home. The receiver magnet EM is held during the clearing process by the earthing of contact O.