Patent GB-485327-A (GB)
Title: Improvements in or relating to printing telegraph exchange systems
IPC: H04L12/00
Filed: 1937-04-19
Abstract: 485,327. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES. April 19, 1937, No. 11124. Convention date, April 20, 1936. Addition to 471,406. [Class 40 (iii)] An exchange system which gives a release signal to both the calling and called parties on occurrence of a release condition at the exchange due e.g. to interfering signals, has means for maintaining the condition until the whole of the connection is released. In the arrangement shown in Fig. 3 for transmission between two junctions FL1, FL2, a release signal, which may be an interfering signal, arriving over FL1 changes ER1 to marking (z) for a relatively long period, the signal being re-transmitted over FL2 by SR2. Relay G1 which is operated during transmission and not released by ordinary marks falls back slowly followed by another slow relay F1 so that during the release period of F1, the contact of ER1 is entirely disconnected from SR2, which is thus prevented from changing over and thus maintains the release signal over FL2. Relay F1 operates SR1 to marking whereby a release signal is sent back over FL1. The release period of F1 is sufficient to permit release of the whole connection. A relay chain or time switch may replace relay F. Another arrangement, Fig. 2 (not shown), in which relay ER1 is shunted by contacts of F1 and G1 is embodied in the exchange circuits described below. Exchange operation, Figs. 5 and 6, for outgoing connections. The calling subscriber TS throws key ET to operate R(i) whereupon line switch VW hunts for an idle group selector GW and telegraph relay ER reverses its contact to spacing by energization of winding (ii). When test relay T operates in series with CI on finding a group selector, SR is reversed to spacing by +ve battery on the b wire and L(ii) pulls up in series with SR. Relay L connects ER(ii) to subscriber's line, reverses the line current, disconnects R from the line and holds it locally over both windings. The current reversal operates E followed by U which switches on the motor M, completes the loop independently of key ET and removes the shunt on the telegraph set EM, sk. The starting of the motor indicates that the subscriber may dial the wanted number. The breaks of the 1st digit reverse ER thereby operating A1 which impulses the vertical magnet H1 of the group selector, R remaining held during digit transmission. The group selector hunts for a repeater U in known manner until stopped by test relay P1 which pulls up in series with S(i) and C2(i) at the repeater. Relay S connects up the repeater which is normally connected to an incoming final selector LW, and when test relay P 1 shunts its high resistance winding (ii) to busy the repeater, C2 pulls up and cuts in its winding (ii) emphasizing the busy condition, the contacts of RU and F which busy the repeater when seized on an incoming connection being disconnected from the test circuit and the seizing circuit of the final selector being opened. Relay RV is not operated by winding (iii) in the test circuit. The sending on relay EU is now connected over the a wire to the contact of ER and reverses its contact. A return signal from the distant end of FL (see next paragraph) reverses SU whereupon RU pulls up, holds S over (ii) and operates F which connects the contact of SU to relay SR of the calling subscriber and inserts a resistance Wu to balance RU ; + battery over su maintains L and SR in the calling line. Incoming connection. The reversal of the contact of distant relay EU when the toll line FL is seized results in SU reversing its contact whereupon RU pulls up, short-circuits its winding (ii) to prevent release by impulses, prevents seizure of the repeater for an outgoing call by opening the c wire from the group selector, and seizes the final selector LW over the c wire. Relay F also pulls up to connect the contact of SU to impulse relay A3 at the final selector, the test circuit of which has been prepared by operation of C3. Resistance Wu balances the winding of RU and this relay has also connected + battery on the b wire to EU which reverses its contact to bring about reversal of the SU relay at the distant end. The two final digits are repeated from EU in the originating exchange to SU which repeats them to A3 at the final selector LW. If the wanted line is idle, test relay P3 switches through and relay T of the wanted line pulls up to connect SR and L to the contact of SU whereupon the contacts SR and L change over. The reversal of the charge on condenser C of the wanted subscriber operates E followed by U which starts his motor, and completes the loop, whereupon relay ER of the wanted line changes over and R pulls up. Release. Key ST is opened by the calling party sufficiently long to ensure the release of relay R by ER whereupon the c wire of the line switch is opened, T falls back and the line switch goes home. Relay T also connects SR and L to negative battery so that these relays restore and the line circuit assumes normal condition. The relapse of C1 at the group selector opens the outgoing c wire to release P1 which restores the selector, and to release C2 at the repeater, S remaining held over (ii). The release signal of the calling party has been transmitted by relay EU at the originating exchange to SU at the distant exchange whereupon RU is shunted down, F and S(ii) relapse and the repeater at the distant exchange is normal. Relay RU opens the c wire to the final selector to release it, and changes over EU which sends back a release signal to reverse SU at the repeater in the originating exchange so that RU thereat falls back slowly followed by F and S to restore the repeater to normal. The relays RU and F at the distant exchange short circuit the relay SU which is transmitting the backward release signal to prevent it changing its condition until the repeater at the originating exchange has restored. The connection is released in a similar manner by the called party and also by an interfering impulse of sufficient duration. Further, the incoming repeater is released before the outgoing repeater and the maintenance of the release signal prevents re-seizure of the incoming repeater in another call.