Patent GB-341603-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/58
Filed: 1929-11-07
Abstract: 341,603. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, CHRISTIAN, D. A., Morven, Charlton Road, and LONG, D. P., 41, Little Heath, both in Charlton, both in London. Nov. 7, 1929, No. 33986. [Class 40 (iv).] In a district office system, a repeater seized on initiation of a call causes two non-numerical switches to hunt for an idle main exchange junction and an idle discriminator respectively. If the first two digits indicate a local call, the junction is released and the non-numerical switch which seized the discriminator hunts for an idle group selector over another portion of its bank. Special junctions, such as junctions to a manual position or to another district office or to the main or other exchange may also be reached over either of the non-numerical switches which are directed in search of these junctions by the discriminator. In the arrangement shown, zone metering equipment is associated with the discriminator which, in the case of main exchange calls, is held until the called party replies, but in a modification, this equipment is associated with the repeater so that the discriminator may, in all cases, be released immediately discrimination has been effected. In both the arrangements described, the special junctions are reached only over the switch which gives access to the main exchange junctions. Local call. On seizure of the repeater by a line switch, relay A operates V which completes driivng and test circuits for non-homing switches JF and DF. Switch JF, which hunts for a junction, has two test banks, JC1 having terminals of special junctions grounded while JC2 has terminals of main exchange junctions grounded. Magnet MJ is operated over JC1 by ground on busy main junctions or on special junctions, and test relay TJ(i) operates in series with magnet MJ to ground over wiper JC2 when it is not short-circuited by ground over JC1. Switch DF operates in a similar manner, terminals of local selectors being grounded in DC1, while terminals of discriminators are grounded in DC2. When DF switches through a series circuit over wiper DA is completed for N and L in which N alone energizes and connects magnet M of the discriminator to wiper DB, dialled impulses being repeated to M and D in parallel over a3. Assuming a local connection is required (first digits 5, 6), relay MK energizes and locks when D relapses at the end of the first digit, and after the next digit, ground connected to the junction of the windings of N operates L which locks up, releases TJ and the main junction, switches the speaking leads through to DF, and reverses the connections of test relay TL to wipers DC1, DC2. Relay N in the discriminator falls back and completes a homing circuit for M. The windings of TL oppose each other so that momentary energization of (ii) over DC1, l3, MD releases TL, TL(ii) being then shortcircuited over wipers DC1, DC2. The switch DF is stepped in a circuit MD, v4, tl1, l2, DC2 over terminals of discriminators, there being no circuit for TL(ii) which is either short-circuited or opencircuited over DC1, but when it reaches the group of terminals of local selectors, it is stepped forward by ground over DC1, TL(ii) until TL(ii) is no longer short-circuited by busy ground over DC2. Call to main exchange. Relay J in the discriminator is operated by a first digit 1 to 4 or 6 to 9, or by a digit 5 followed by a second digit other than 6, connects ground over a high resistance and DB to relay TT which does not operate, and opens the impulsing circuit to M. The call is completed over the junction in normal manner. Call over special junction. In response to digit 0, relay TK in the discriminator pulls up and connects direct ground to TT which reverses the connections of TJ to the test wipers of JF so that this switch hunts in the group of special junctions in the same manner as DF hunts for a local selector. Metering and release of discriminator. The answering supervisory relay Y prepares delayed metering circuits comprising relays S, Z completed over cams CS, CZ, and, in the case of a local call, since TJ has been released, simple fourth-wire metering takes place over tj4, z1, s1. The discriminator was released previously as described above. In the case of calls over main or special junctions, the discriminator is not released until metering has been effected and either or both relays B, C are operated in accordance with the setting of the discriminator to connect one of the repeated metering cams MMC over wiper DM to contact tj4. As relay TJ is still operated in these cases, repeated metering occurs during the period when both S and Z are operated over cam CZ. During the metering period, V is held over contacts of S and Z. When S falls back, JT operates and opens the circuit of TL which releases N to home the discriminator. The meter may be of the continuous recording type registering in accordance with duration of conversation, the rate being varied by relays B, C in accordance with the zone. Modified arrangement with repeated metering equipment associated with the repeater. The circuits are substantially the same as those in Fig. 1 except that contacts in bank MM of the discriminator are connected over varying resistances to the contact in bank DM of switch DF, the wiper of which is connected to windings of relays B, C, and JT in series. Relay JT operates, locks up and releases the discriminator as previously described, while neither, one or both relays B, C operate, lock and connect up the requisite metering cam.