Patent GB-534210-A (GB)
Title: Improvements in or relating to teleprinter exchange systems
IPC: H04L12/00
Filed: 1939-06-30
Abstract: 534,210. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Haigh, L. B., Rousseau, E. J., and Clemens, P. J.). June 30, 1939. No. 19116. [Class 40 (iii)] Relates to inter-exchange junction working between teleprinter exchanges, particularly over two-way junctions between automatic exchanges having register controllers. In order that the incoming end of the junction at exchange B may be marked busy from exchange A, e.g. in the event of a fault on the junction, without taking into use the register-controller or other "common" apparatus at exchange B, a special " busying " signal is used which differs from the true calling signal. If spacing current is normally connected to line, the " busying " signal may consist of a marking current; and the true calling signal may consist of a marking current followed by a " spacing impulse," i.e. a change from marking to spacing followed after a short interval by a return to marking. The " busying " marking current preferably has a duration greater than any spacing signal occurring during teleprinter communication, whereby any connection accidentally set up over the junction would be released. A calling line is connected by line-finder LF over contacts of a relay RCR (not shown) to a register circuit which positions the brushes a, b, c, of the first selector in accordance with the first digits of the dialled number. If this digit indicates a junction, as assumed, a relay LOR in the register is energized and starts an impulsing switch IS by energizing its magnet ISM. When the selector brushes find an idle junction, relay GTR energizes in series with relay 20CR over the test lead. Relay GTR energizes relays SHR, OXR, and relay 20CR energizes relay 20DR, which connects brush b to the polarized telegraph relay 2SR and brush a to the armature of relay 2RR in the junction handling signals from B to A. Relay 2SR connects marking current (i.e. the " busying " signal) to the other junction, thereby energizing relay 3RR at exchange B, and this energizes relays 3ICR, 3IDR, 3IER, 30BR in sequence. Relay 3ICR marks the junction busy at exchange B, but a register at exchange B is not taken into use unless this " busying " signal is converted into a true calling signal, as described below. Reverting to exchange A, when the second digit has been received by the register, relay EDR energizes and when the brush of the impulse switch IS passes over its normal contact relay RBR is energized, and locks up. When the brush of switch IS reaches a later contact, relay RER energizes, locks up, and connects spacing current over brush b to relay 2SR, which in turn connects spacing current to relay 3RR, thereby energizing relay 3IPR, which locks up and energizes relays 3RSR. 3RCR. Relay 3RCR takes the register 3RC at exchange B into use, and connects its impulse relay 3IR and impulsing contact 3car2 to the contact 3rrl and relay 3SR respectively. When the brush of switch IS reaches a later contact, relay RDR is energized and releases relays RBR and RER, thereby connecting marking current to relays 2SR, 3RR. A circuit for relay 3IR of the register at exchange B is now completed over its associated rectifier and the contact of relay 3RR. Relay 3IR energizes relay 3CAR which prepares a circuit for the stepping magnet SM of the register, and energizes retay 3SR, which in turn causes relay 2RR to energize relay RIR at exchange A. This causes the register at A to send impulses corresponding to the next digit, these impulses being repeated by relays 2SR, 3RR, 3IR. When the wanted line is found, relays THR (not shown) are energized at both exchanges and complete the connection.