Patent GB-241655-A (GB)
Title: Improvements in circuit arrangements for automatic telephone systems and the like
IPC: H04Q3/00
Filed: 1924-08-15
Abstract: 241,655. Siemens Bros. & Co., Ltd., and Patterson, W. G. Aug. 15, 1924. Automatic exchange systems.-The circuits of the line and test relays of a rotary line switch are so arranged that if it is released at a selector which it has seized while the subscriber's line remains bridged, the switch steps on without seizing a further selector and comes to rest on its normal last contacts, over which a tone signal is sent back. This action may take place if the subscriber omits to dial, or if the line switch is started up by a fault in the subscriber's line. Specifications 22804/11 and 168,134 are referred to. First arrangement, Fig. 1. The line relay R is connected to the subscriber's line over the first and last contacts of an extra wiper E, and is held over its contact r3 during rotation. When release occurs at the succeeding selector, the test relay T falls back and cannot re-energize since contact r1 is open. The switch steps on. and when the last contacts are reached, if the line is bridged, relay R energizes over wiper E, and relay T operates, the last contact of the test wiper C being disconnected, and opens the driving circuit. Relay R locks over the A. and B-wipers and cam springs CI, and a busy tone is fed back over a transformer BB, as in the case when all the outgoing lines are busy. The switch moves to normal when the subscriber hangs up, or when the fault is cleared. Second arrangement, Fig. 2. The wipers when in normal position bridge the first and last contacts, and the penultimate contacts are not connected to a selector. The line relay R energizes over the first and last contacts of the A-wiper, and holds independently of the calling loop during hunting over contacts r1 and the test wiper C, and falls back when the test relay T operates. During the restoring movement, the test relay is disconnected at contact r2, and relay R energizes over the penultimate contact of wiper D, and connects the magnet RM to this contact. Relay T is short-circuited over the penultimate contact of wiper D, but energizes at the next step and open-circuits relay R. If, however, the line is bridged, relay R remains operated over the last contacts of the A- and B-wipers, and stops the rotation of the switch, and a busy tone is fed back as before. Third arrangement, Fig. 3. If the last contacts are reached before an idle outgoing line is found, the hunting operation is repeated. The line relay R energizes over the first and last contacts of the A-wiper, but is released during hunting, and re-energizes when an idle line is found over an extra wiper E, to which ground is connected by the release relay of the seized selector. The magnet RM is connected up first over front contact r1 and wiper D, and then over back contact r1 and the test wiper C. If no idle line has been found when the last contacts are reached, the magnet RM finds a circuit over contact r3 and wiper D, and the switch rotates a second time. When an idle line is found, relay R reenergizes and locks over contact r2 and wiper D. so that in the restoring movement, relay T is disconnected at contact r2 and the last contacts are reached with relay R operated, and the driving circuit is opened. Contacts rm2 are opened, but before relay R has time to relapse, relay T energizes over contact r3 and wiper D and connects relay R to the line over the A- and B-wipers. If the line is bridged, relay R remains held, and a " number unavailable " tone is fed back. Fourth arrangement, Figs. 4 and 5. An idle outgoing line is indicated by battery on the test contact. The test relay T energizes when an idle line is found, locks and opens its energizing circuit at contact t4, which is latched so that it can only be closed again in the position of the switch. Relay T energizes over the test wiper C when the last contacts are reached if the line relay R is operated, and stops the switch, and a busy tone is fed back. The latch 9, Fig. 5, controlling the contact springs 12, 13 co-operates with pins 5, 6, 7 carried by a disc on the wiper shaft. Two further modifications are mentioned in the second Provisional Specification in which (1) the line relay is connected to the line only in the first and last positions of the switch, and the test relay energizes over battery on the last test contact if the line relay is operated, and (2) if the line relay energizes over the last contacts, the driving circuit is opened by this relay.