Patent GB-487476-A (GB)
Title: Telegraph line circuits for teleprinter exchange systems
IPC: B66D1/48
Filed: 1937-10-14
Abstract: 487,476. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Oct. 14, 1937, No. 27959. Convention date, Oct. 14, 1936. [Class 40 (iii)] A repeater R is connected between a subscriber's line 13 and jack 16 when the exchange has been called by the subscriber's applying positive potential to the line 13, which when idle is earthed through a bell 14 ; and the supervisory relays D, E, which are connected to the subscriber's line, in the idle state, are transferred to circuits on the exchange side of the repeater R during transmission of messages. Subscriber calling exchange. The subscriber calls by applying positive potential to the line 13, whereupon relays D, TL pull up and operate the lamp CL and night alarm. Relays E, F, and C pull up, connecting line 13 to repeater R via conductor 23. At the same time relay C causes lamp AL to light up, and the operator inserts his plug (not shown) in the jack 16. Battery in the cord circuit causes relay G to pull up, putting out the lamps AL and CL and extending the message circuit, which passes from the repeater through conductor 17 and relay winding B, to the ring 16r of the jack. During a message, relay B follows the signals but slow-release relay F, which it controls, holds on and keeps relays C and J energized, transferring the control of relays D, E to the clearing relay A, so that the unpolarized relay D stands operated while the polarized relay E is released. Break signal from subscriber on jack circuit. This consists of negative potential applied to the line 13, which causes release of relays B, F, C. Relay C releases the slow-release relay J, but in the interval between the releases of these two relays the line 13 is able to discharge through a resistance 16a, to prevent the subsequent false operation of test relays D, E. These relays are transferred back to the line 13, the unpolarized relay being energized while the polarized relay E is released by the negative (spacing) potential; but on the resumption of traffic after the end of the break signal, relay E and consequently relays F, C, J and B pull up and the working condition is restored. Break signal from subscriber on cord circuit. This comprises a long spacing condition and causes relay B to release, followed by relays F, C and J. Relay E now finds positive polarity on the line 13 and pulls up, reoperating relays F, C, J, whereupon relay E releases, and this cycle of operations repeats so long as the break signal continues. Clearing. The clearing signal is made by opening the line 13 at the subscriber's station. Relay B releases, followed by F, C & J, the line being discharged through resistance 16a between the release of C and that of J. Release of J is followed by release of test relay D, whereupon relay A pulls up, breaking the message path and connecting earth to the tip of the cord at 16t to operate a supervisory lamp in the cord circuit (not shown). Recalling switchboard operator. The recall key at the subscriber's station opens the line for a short interval and then recloses it. Relay D is temporarily released, whereupon relay A pulls up and grounds the tip of the cord to give a recall signal. Exchange calling subscriber. The operator calls by inserting a plug in the appropriate jack 16. Relay G thereupon pulls up, followed by A, closing a circuit through the ring of the plug for relay H and A.C. source AC. Relay J therefore pulls up and ringing current is applied from the source AC to line 13, which discharges through resistance 16a at each release of relay H. Half-duplex system. The arrangement described as applied to differential duplex may be modified, using the additional line 13A and throwing the switches 19, 21, for a half-duplex system in which conductors 13, 13A respectively convey signals from and to the subscriber's station.