Patent GB-399632-A (GB)
Title: Improvements relating to automatic and semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1932-07-26
Abstract: 399,632. Automatic exchange systems. SIEMENS BROS.- & CO., Ltd., Caxton House, Tothill Street, CLARK, R. I. H., 65, Humber Road, Blackheath, CHRISTIAN, D. A., Morven, Charlton Road, Charlton, and TEES, J. E., 27, Elderslie Road, Eltham, all in London. July 26, 1932, No. 21041. [Class 40 (iv).] In a final selector available in common to local subscribers and operators and to trunkoffering operators at a distant trunk exchange, the usual feed bridge is disconnected from the talking wipers and the normal ringing and busy signalling arrangements are rendered ineffective on trunk calls, the feed, ringing and signalling currents being supplied at the incoming selector. The incoming and intermediate selectors for trunk calls have, in addition to the usual test wipers P, wipers +, - for extending the talking circuit, wipers M, N over which the setting of the switches ahead is controlled, those of the last intermediate selector engaging the local talking inlet of the final selector, and wipers TL for extending a signalling' circuit. Specification 372,004 is referred to. Setting incoming and intermediate selectors. When the junction is seized, line, dialling and release relays A, C, B, Fig. 1, pull up. A repeats the first digit to VM. C falls back at the end of the digit to energize RM, which at the end of its stroke completes the test circuit. If the line is busy, H is shortcircuited and G pulls up and releases the magnet which releases G and then pulls up again. When an idle line is found, H switches through and B falls back, subsequent digits being repeated by A over M, N. Intermediate selectors, Fig. 2, are controlled in a similar manner. Setting 200-point final selector, Fig. 3. If the switch is engaged over the lower pair M, N, WC is operated temporarily in series with the line relay A and release relay B then operates the wiper changing relay WS. Dialling relay C pulls up on the operation of B and at the end of the tens digit energizes E, which switches over from VM to RM and reoperates C. At the end of the digit C releases E to make a fleeting test circuit. Completing trunk call to idle line. If the line is idle, H completes a circuit over TL for T, Fig. 3, and SF, SB, Fig. 1, in series. All these relays pull up, SF nullifying the action of SB, and T, Fig. 3, switches the talking wipers from the local to the trunk talking circuit. On the operation of the ringing key, which grounds the lower junction wire, TO is unbalanced and energizes RA which completes the ringing circuit over F and a separate ring-hack tone circuit. When the subscriber replies, F releases RA and connects up the back-bridge relay D which reverses the connections of the line relay to give the usual signal. Offering trunk call to busy line. If the line is busy, the relapse of E energizes G which completes a circuit over TL for T, Fig. 3, SF, SB in series in which only SB is able to operate. SB connects an intermittent tone source to the upper junction wire and connects an interrupter to BH which thus connects battery to. the upper junction wire during the silent intervals to give a flashing signal. If the line is busy in a long-distance call continuous tone is present on its test terminal either via contact t4 in another final selector or via a circuit in the outgoing repeater (not shown) and the subscriber's line circuit which may be of the type described in Specification 393,089. This tone current passes via TL and bh1 to the upper junction wire during the silent intervals of the ordinary tone signal. The trunk offering key unbalances TO in the same way as the ringing key but in this case TO-energizes T, Fig. 1, which puts full ground on TL to operate T, Fig. 3, releases SB to stop the busy signal and completes the talking circuit. The restoration of the trunk offering key releases TO, T, Fig. 1, and the busy signal is again connected up. T, Fig. 3, however, remains locked over its winding (iii) so that when the wanted party clears H pulls up energizing SF to stop the busy signal. The line is then rung and the connection is completed as described above. In case the subscriber removes his receiver before he has been rung the operator can speak to him over contacts sf4, sf5. Release. If the operator clears before the subscriber, the switches are held by the bridge at d3, Fig. 1. Normally the relapse of D, Fig. 1, when the called party hangs up gives the clearing signal. The operator may in these conditions re-ring the line if necessary. When she removes the plug the relapse of A releases the final selector, which is followed by the remaining switches. All outlets busy. In these circumstances the operator hears the interrupted busy tone over 11th step contacts but receives no flashing signal. Operation of final selector in local calls. The switch is set as previously described and, there being no circuit over TL, the line is rung in the usual way. The relays A, D provide the usual talking feed and the call is boostermetered in known manner with the help of an impulse-timing relay J. If the line is busy, G connects up busy tone and flash in known manner and holds B during the silent intervals.