Patent GB-360009-A (GB)
Title: Improvements in or relating to telegraph exchange systems
IPC: H04L12/00
Filed: 1930-07-25
Abstract: 360,009. Telegraph exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, and HARRISON, H. H., 15, Mayville Road, Mossley Hill, both in Liverpool. July 25, 1930, No. 22504. [Class 40 (iii).[ In a printing-telegraph exchange system, the connection is extended towards a desired subscriber by a step by step automatic switch which is stepped by the intermittent operation of a polarized relay operated by a series of impulses comprising reversals of current sent over a two-conductor telegraph line. When the subscriber, Fig. 1, desires to make a call he moves the non-locking key NLK so that at spring 3 a circuit is completed through the impulsing dial CD and the relays R1, SR. The relay R1 reverses the direction of current from a battery B to the line L1, L2 when a relay R2, energized over the contact of SR and the closed springs DONS of the dial, changes over the line connection from the polarized relay PR of the telegraph apparatus. The polarized relay NPR at the exchange, Fig. 2, completes the circuit of a guard relay GR which locks up over GR1 and applies positive potential over GR2 to mark the calling subscriber " busy." At GR3 it energizes a relay R which, at its contacts R1, R2, prepares a circuit for a return signal. The dialling of the desired number intermittently de-energizes the relay R1 with consequent current reversals over the lines L1, L2. The reversed currents cause the relay NPR to energize intermittently the stepping magnet DM. If the called line is free, the test relay TR operates, and short circuits one winding to mark the called line " busy." The contact TR3 breaks the circuit of the relay R which, until it releases, sends current over the line to operate the relay PR, Fig.1, energizing the starting magnet of the telegraph apparatus of the calling subscriber. Rotation of the cam RC1 operates a trembler bell RL, and the apparatus at the called subscriber is set into operation by current transmitted on actuation of the arm TL at the calling station. To break the connection the operation of a release key RK energizes a relay RR, Fig. 2, which closes a self-interrupting circuit for the stepping magnet DM and breaks the circuit of the guard relay-GR. The switch is stepped around to its normal position where the locking circuit of relay RR is broken. In a modification of Fig. 2, Fig. 3 (not shown), if the called line is engaged, a slow-operating relay is energized and connects to the line, current in such a direction that the armature of a polarized relay at the calling station instead of operating the starting magnet, completes the circuit of a buzzer which continues to sound until the connection is broken down as described in connection with Figs. 1 and 2. A connection between calling and called subscribers may be established over a preselector, Fig. 4, a group selector, Fig. 6, and a final or line selector, Fig. 5. Preliminary selection. When the line is taken into use by depressing key NLK, Fig. 1, the relay NPR energizes the guard relay GR which locks up at contact GR2 and at GR3 marks the line " busy." At contact GR4 it energizes the stepping magnet DM, subsequently operated over the normal contact TR5 of the test relay TR. The switch is rotated until an idle group selector is found, and when test relay TR operates, the line is switched through to the calling subscriber at TR1, TR2. If the preselector fails to find an idle group selector, the switch is stepped round until at the separate contact of the fifth wiper, the relay BR is operated and the buzzer at the calling station is sounded. Group selector. Where the selector is taken into use a relay D energizes relays A, B in sequence. The selecting impulses through the relay PR are repeated by relay A to the vertical magnet VM in series with the relay C. On the first vertical step the contact springs N2 are closed, and a circuit completed for a relay E, which locks up through springs RM1, CS1, N2. When the train of impulses has terminated, relay C closes a circuit for the rotary magnet RM in series with the relay E. After the first step the springs RM1 are opened, releasing the relay E. If an idle line selector is not found at the first step, E is again energized and the rotary magnet energized intermittently until either a selector is found, or, at contacts CS2, the circuit of a buzzer relay BR is completed after opening at springs CS1 the circuit of relay E. When an idle line selector is found, the test relay TR opens at contact TR7 the circuit of the rotary magnet RM. Final or line selector. When the final selector is taken into use, relay D, Fig. 5, energizes relays A, B. The tens impulses are repeated by relays PR, A to the vertical magnet VM and relay C, and at the end of these impulses, relay C releases, and the units impulses setting the rotary magnet RM pass in series through a relay E, which at its contacts E1, E2 opens the circuit of the test relay TR and the buzzer relay BR. At contact E3 a slow-release relay F prepares a circuit for a relay R. If, when E releases at the end of the impulses, the test relay TR operates, contact TR3 energizes the relay R which transmits starting current to the calling subscriber until the relay F falls off, and contact TR4 opens the circuit of the buzzer relay BR. If the test relay TR is not operated, the slowacting buzzer-relay BR is energized over the springs NR closed on the first step of the rotary magnet RM, to sound the buzzer at the transmitting station. Release of connection. Release is effected by operating the key RK at the calling station, Fig. 1. The relay RR, Fig. 4, thereby energized, opens the circuit of the test relay TR, which closes the circuit of the magnet DM, rotating the switch to its offnormal position. At contact TR5, Fig. 4, the circuit of the relay D, Fig. 6, is broken and relays A, B release. The release magnet ZM restores the switch to normal and at spring Z, Fig. 6, the circuit of the test relay TR is opened. When the relay TR, Fig. 6, releases, the relays D, A, B, Fig. 5, are de-energized in sequence, but an impulse is sent through relay E which breaks the circuit of the test relay TR, Fig. 5. Relay B energizes release magnet ZM. The group selector, Fig. 6, or the rotary switch, Fig. 4, may be omitted from the system.