Patent GB-281407-A (GB)
Title: Improved circuit arrangements for hunting switches in telephone systems
IPC: H04Q3/00
Filed: 1926-09-04
Abstract: 281,407. Siemens Bros. & Co., Ltd., and Humphries, H. E. Sept. 4, 1926. Automatic exchange systems. - The circuit arrangements of electromagnetic hunting switches are such that a test as to the condition of a link is made prior to the arrival of the talking wipers on the link. This may be effected by providing a special test wiper one step in advance of the other wipers, or alternatively, the positions of all the wipers may correspond, the bank engaged by the special test wiper being suitably wired so that the link tested is one ahead of that engaged by the other wipers. Fig. 1 shows a line-switch of the normal type having wipers A - - D normally just out of the bank and an advanced wiper C<1> normally engaging with the first outgoing link. The switch is of the reverse-drive type and the circuits are such that when wiper C<1> engages a free link, the test relay T closes a circuit for maintaining the driving magnet energized independently of its interrupter contacts so as to prevent overstepping. Similar advanced testing may be employed in a call-finder, but Figs 2, 3 show an arrangement for a two co-ordinate finder in which the test for the calling line is made over the speaking conductors and the advanced wiper D<2> controls a relay F which opens the speaking wire circuits to prevent interference when passing over busy lines. An idle finder is preselected by an assigner and a common line relay DP is allotted to each of the ten lines in a level and serves to start the assigned finder. Other features of the system shown in Figs. 2, 3 are claimed in Specification 282,185. Line-switch, Fig. 1. The line relay R connects winding 1 of the test relay T to the advanced test wiper C<1> and completes a &eH- interrupting circuit for magnet DM over contacts r5. When wiper C<1> reaches an idle trunk, relay T engergizes, locks momentarily to earth over contact r4, disconnects relay R, and shortcircuits interrupter contacts dm thus maintaining magnet DM energized. When relay R relapses, magnet DM de-energizes stepping the remaining wipers on to the selected trunk, and relay T remains locked over wiper C. The a-and b-wires are opened during stepping at contacts r2, r3, which may be weighted so as to fall back slowly thus ensuring that the speaking wires will not be closed until the wipers have been stepped on to idle contacts. Finder, Fig. 2. When the line a, b initiates a call, line relay DP, Fig. 3, common to all the lines in the same level, energizes and, in the manner described in a later paragraph, effects the connection of interrupter I<1> over wiper A<2> and lead 7 to relay L in the assigned finder. Relay L completes a circuit t5, kk2, l6, for the finder vertical magnet VM in series with a second interrupter I<2>. The wipers are thus stepped up until an extra vertical wiper E' reaches the calling level when relay E energizes over contact dp2 and connects up the rotary magnet RM in place of the vertical magnet. When the calling line is reached, relay R operates over contacts l5, f3, wiper B<1>, loop a, b, and contact co1, releases relay L, and holds magnet RM operated over contact r2. The release of relay L connects battery over contact f4 and wiper C<1> to operate the cut-off relay CO. During the rotary movement, if the advanced wiper D<2> encounters a busy line, relay F is operated over contacts rm, l4, to disconnect talking wipers A<1>, B<1>. When the remaining wipers are stepped on to the busy line, relay F remains operated over wiper D<1>. If the succeeding line is also busy, the circuit over wiper D<2> will again be completed but if the succeeding line is idle, relay F will de-energize as soon as wiper D<1> leaves the busy line. Group selector, Fig. 2. Relays A, V, D operate, the latter connecting up dialling tone from lead 6. Impulses are repeated at contact a1 to the, vertical magnet VM<1> in series with winding 2 of relay D, and at the end of the digit the relapse of relay D completes a selfinterrupting circuit for the rotary magnet RM<1>. When an idle trunk is found relay T operates over winding 1, locks over winding 2 and directly earths the test wiper. Further impulses are repeated over the b-wire in series with relay R and when the called subscriber replies relay Y operates over the a-wire and releases relay E. Release of finder and group selector. When the calling subscriber hangs up, relays A,V,T release in succession and close the circuit of the selector release magnet MM<1>. The restoration of off-normal contacts kk2 completes a circuit over contacts t5, d1, l6, k2, e3, for winding 2 of relay F which closes a parallel circuit for the finder release magnet MM. Relay F opens the speaking conductors to prevent interference with busy lines during release. Assignor, Fig. 3. Normally the wipers A<2> - - C<2> of the assignor are in engagement with an idle finder and relay AT is energized over wiper A<2> and lead 7 in series with relay L which however does not energize. The operation of a line relay DP on the initiation of a call charges condenser QA which discharges through relay AF and this relay starts up interrupters I<1>, I<2> and locks up in series with relay AG. When earth is again connected up at interrupter I<1> relay L energizes as already referred to. The operation of relay AF also energizes relay AH which short-circuits all unoperated line relays. The operation of relay AG causes the relapse of relay AT and in turn its own release so that when the, interrupter I<2> next connects battery to relay AM, impulses are transmitted to the assignor magnet DM as well as to the finder magnets When an idle finder is reached relay AT energizes again over wiper A<2> and lead 7 to stop the hunting. When both finder and assignor have completed their operations the discharge of condenser QB energizes relay AB which by the operation of relay AC effects the short-circuiting of all line relays. If no idle finder is found. the assignor is stopped in a normal position owing to the, operation of relay AT over wipers A<2>, B<2>, and relay AH is operated over wipier C<2> to prevent the operation of any line relay. As soon as a finder becomes available, relay AT is short-circuited over lead 3 and hunting recommences. Specification 240,996 is referred to.