Patent GB-440291-A (GB)
Title: Improvements in and relating to telegraph exchange systems
IPC: H04L12/00
Filed: 1934-10-16
Abstract: 440,291. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. Oct. 16, 1934, No. 29620. Convention date, Oct. 16, 1933. [Class 40 (iii)] Relates to an automatic exchange system in which a trunk connection between two twowire subscribers' lines passes through repeaters at each end of the four-wire trunk line and junction lines, and the calling impulse (whereby the line-condition which obtains during idle periods is reversed) is sent out by the calling subscriber and repeated back by the called subscriber. According to the invention there is associated with the repeater at each exchange a relay S having coils SI, SII which, when the clearing signal has been given, maintains an engaged condition until both subscribers' circuits have been cleared, and so prevents the hunting action that might otherwise be set up by the repeated-back impulses. Lay-out of system, Fig. 3. The calling subscriber TS1 emits a call to the preselector VW1 at his exchange FA1 through a group selector GW1 and repeated U1 at that exchange, over a trunk line F2 to a repeater U2 at the distant exchange FA2, and through a line-selector LW2 at that exchange to the distant subscriber TS2. Fig. 1 shows a subscriber's station TS, a preselector VW, groupselector GW and line-selector LW, while Fig. 2 shows a repeater U, these figures being applicable to both halves of the system shown in Fig. 3. The first group of dialled impulses selects a set of trunk circuits, of which a free one is found by the group selector. The second group of impulses selects a distant station served by that set of trunk circuits. Finding a group selector. A call is initiated at TS1 by momentarily closing the key ET, Fig. 1, so as to energize the slow-release magnet R through the telegraph battery TB. Contact r2 starts the presel.ector VW which, driven by the interrupter UVW and stepping-magnet DVW, hunts for a free group selector GW. The testing-magnet T then cuts off the stepping- circuit and marks the group selector busy with its contact t1 Preparation of calling subscriber's local circuits. Contact t2 reverses the current through relays L, SR. Contacts l1, l2, l3 reverse the battery-connections of the subscriber's loop, and the armature er is shifted to the spacing position, while relays E, Ul, start the motor M, short-circuit the condenser c, and bring into circuit the transmitter sk and receiver EM. Dialling of first group of impulses and finding of a repeater and trunk circuit. The dial switch NS causes the armature er to repeat dialling-impulses to the group-selector magnet A1, whose armature a1 operates the lifting-magnet H1 to raise the group-selector switch to the desired level. The rotary magnet D1 then causes the selector to hunt for a disengaged repeater U, Fig. 2, with its associated 4-wire trunk line FL. In the testing-circuit c the busying-relay P1 pulls up and completes the limbs a, b, at p11, p12 ; while winding I of relay s causes the repeater-connections to be transferred at sl, s2, to the group selector GW, Fig. 1, from the corresponding line selector LW which is left idle ; sending-on relay EU thereupon shifts its armature eu to the spacing position. When relay P1 marks itself busy, winding II of relay C2 is able to pull up, and the operation of contacts c21, s3, guards the line selectors LW of the calling end from subsequent operation by the return impulse ; this would otherwise occur in the manner described in the next paragraph. Preparation of distant repeater. Armature eu, Fig. 2, of the near repeater U1, Fig. 3, on assuming the spacing position sends forward an impulse to the repeater U2 at the distant end of the trunk line : Fig. 2 now represents this distant repeater U2 instead of representing the near repeater U1 as it did in the preceding paragraph. The impulse is received by relay SU, and armature su then shifts to the spacing position so that the supervisory relay RU, which is quick-acting but slowreleasing, pulls up. Relay RU at ru1 reverses the current through the relay EU, so that . armature eu assumes the spacing position. At ru2 the group selector GW is disabled by the breaking of the test line c, and through ru4 the magnet F is energized but coil SII of relay S is unable to pull up, being only capable of holding on. Contact f4 brings in a resistance Wn to balance the winding RUI during the signalling of messages by armature su. Return impulse from distant exchange. When armature eu at the distant repeater U2 assumes the spacing position, as described in the preceding paragraph, an impulse is sent to the relay SU of the near repeater U1, whose armature su moves to energize the supervisory relay RU. Windings F and SII at U1 are brought into circuit and contact f<3> completes the b line to the group selector GW through the existing contact at s2. Contact f<3> ensures that relays L, SR, Fig. 1, shall not be connected to contact su until the latter has assumed the (spacing) polarity requisite to avoid disturbing them. Dialling of second and third groups of impulses and selection of called station. The first group of impulses selected a group of trunk circuits out of which a free circuit with repeaters U1, U2 was found by the group selector. The second group is now sent, operating the magnet A3 at exchange FA2, so that contact a3 operates the lifting-magnet H3 of the line-selector LW. The third group of impulses similarly causes contact a3 to operate the rotary magnet D3 to select the called station, the leads a, b, c of the line-selector LW being multipled, Fig. 1, to those of the preselector VW. The test relay P3 on pulling up completes the leads a, b, at p31, p32. The local circuits of the called station are then prepared by relays T, SR, L, E, U, ER and R as in the case of the calling station. Release by calling station. The releasing key ST at the calling station causes contact er to mark for long enough to reverse the relay R. Relays C1, T, L, SR follow, and the preselector VW is stepped home when contact t1 drops. When the releasing key ST is closed relays E & U are restored and motor M is stopped. Relay PI is disconnected at c11, and group selector GW is thereupon stepped home; slow-release relay C2 releases, but relay S is held on by its winding SII. Before the slow-release relay R at the calling station dropped, the opening of the clearing-key ST caused contact er to send a marking impulse to the distant repeater U2, where the armature su caused relay RU and consequently relay F to drop, but where relay S is still held on by windings SI. At the called station the release of relay RU causes the local circuits to be restored similarly to those of the calling station. Return impulse during release by calling station, and function of the relay S. The release of the called station causes a marking impulse to be sent back to the calling station, where armature su moves to its idle or marking contact (as shown) and slow-release supervisory relay RU drops. Winding SI of relay S has already been de-energized during restoration of the group selector GW, but winding SII has held on until cut off at ru4. Thus relay EU cannot acquire a spacing current from contact p32, being cut off at sl, until the release of RU, whereupon it is cut off at ru1. Hunting would be set up by return impulses passing between the two stations, but for the relay S at the calling station which holds on until connections have been cleared at both ends of the trunk line. Release by called station or both stations. When the called subscriber opens his clearing- key ST, the consequent release of magnets R, RU at his end of the line does not effect release, but the long marking impulse sent over the line to the calling station releases relay RU at the distant exchange and the clearing operation proceeds as described in the preceding paragraph. When both subscribers clear at the same instant the clearing process starts at both ends, but faults are prevented by the fact that relay S at the calling end does not release until the line has been cleared on both sides.