Patent GB-534459-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04L12/00
Filed: 1939-06-30
Abstract: 534,459. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Haigh, L. B., Rousseau, E. J., and Clemens, P. J.). June 30, 1939, No. 19117. [Class 40 (in)] Relates to automatic teleprinter exchange systems using register controllers to control switching means such as selectors. The signal from the switching means to the register controller to indicate that the switching means is in a condition to be controlled comprises a change from spacing to marking conditions. In the system described, a calling line (represented only by a relay SR and the contacts rrl of a relay RR not shown) is connected by a line-finder LF over the contacts of a relay RCR (not shown) to a register controller comprising stepping switches SM1, SM2 responsive to the dialled impulses, a stepping switch SM3 controlling the sending of impulses over the wipers of selector S to the next exchange, and an impulse switch IS. If, as assumed, the first digit dialled indicates a junction to another exchange, the selector S is positioned by circuits not shown. When an idle junction is found, relay OXR is energized, and connects positive potential over brush b1 to relay IR at the distant exchange B. When the register at exchange B has been connected up, relay RHR energizes relay CAR which locks up, prepares a circuit for the stepping magnet SM4 and connects positive potential over contacts bpr1, pir1, car1 and brush a1 to the relay RIR at exchange A. This positive potential indicates that the register at B is ready to receive impulses. Relay RIR is energized by this potential and in conjunction with relay EBR (energized when sufficient digits have been received by the register at exchange A) closes a circuit for relay OPR over a contact of the impulse switch IS. Relay OPR prepares a circuit for OQR which energizes when switch IS moves off its contact and causes relay OSR to connect negative potential over brush b1 to de-energize the relay IR at exchange B. Relay OSR is impulsed by switch IS and connects positive and negative alternately to relay IR at the same time stepping switch SM3 until its wiper S3b reaches the contact earthed by switch SM1, whereupon relay CXR disconnects the impulsing circuit at cxr1 and energizes relay SAR, which prepares a circuit for SBR. At exchange B, the selecting impulses are repeated by relay IR to stepping magnet SM4 through a slow-release relay LMR which causes relay PIR to connect positive potential over brush al to relay RIR, which remains energized. Relay PIR also energizes a slow-release relay BPR so that when the series relay LMR, at the end of the impulse train, de-energizes relay PIR, negative potential is connected to relay RIR during the release of BPR. This negative impulse causes relay RIR to de-energize relays OPR, OQR, CXR, thereby energizing relay SBR which makes switch SM2 operative in place of SM1. At exchange B the release of relay LMR also energizes relay CR (over the off-normal contacts of SM4) thereby connecting SM5 in place of SM4, and the release of relay BPR again connects positive to brush a1 and relay RIR. The negative pulse followed by this positive pulse constitutes a signal that exchange B is ready to receive the next set of pulses. The transmission of the next set of selecting impulses is effected in a similar way.