Patent GB-230521-A (GB)
Title: Improved circuit arrangements for automatic selectors used in telephone systems
IPC: H04Q3/00
Filed: 1923-11-13
Abstract: 230,521. Siemens Bros. &. Co., Ltd., and Patterson, W. G. Nov. 13, 1923. Automatic exchange systems; metering.-In a connector of the Strowger type, the booster metering battery is connected up by the ring cut-off relay F for an interval dependent on the release of the change-over relay G (energized for the second time) or the ringing relay S. In the case of a dead number call, ringing and subsequent metering are prevented by a special potential on the line terminals which either energizes the answering relay D to open the ringing circuit or directly shortcircuits the ringing relay S. If a wanted line is busy, the test relay fails to operate, and busy tone is connected up by the energization of the ring cut-off relay F or the ringing relay S. The change-over relay G is controlled by a slow release relay C which is included in both the vertical and the rotary driving circuits. First arrangement, Fig. 1. Line relay A energizes over vertical off-normal contacts k2, and connects up release relay B, which earths the incoming test wire and locks relay A independently of contacts k2. The tens impulses are repeated at back contact a1 to the vertical magnet VM, slow relay C being energized in series over its winding 1, and releasing at the end of the train to connect up change-over relay G over off-normal contacts k2. The units impulses are thus repeated to the rotary magnet RM, and relay C is again energized, but relay G being slow to release holds up until its circuit is re-made over rotary off-normal contacts w1 and contact c2. Relay C relapses at the end of the train, releasing relay G and connecting winding 1 of test relay H to the test wiper at contact c3. If the wanted line is free, wiper H energizes, locks over its winding 2, earths the test wiper and connects relay D to the line. Ringing relay S energizes over contacts g2, d3, h4 when relay G falls back. locks at contact s4, and applies ringing current to the wanted line over winding 1 of relay F and ring back tone to the calling line. Relay G energizes again over contact s4. When the called subscriber replies, ring cut-off relay F is energized by the increased current, locks over its winding 2 which was previously short-circuited, disconnects ring back tone, and connects booster battery over contacts f5, g5 to the test wire to effect metering. Relay S is also released, and the calling and called lines are connected together. Relay G relapses after an interval and disconnects booster battery, and relay D energizes and reverses the connections of the incoming talking wires. If the wanted line is busy, relay H does not energize, so that the operation of relay S is prevented upon relapse of relay G. Relay C energizes again however over its winding 2 and contacts g3, h4, disconnects relay H at contact c3 to prevent its energization should the wanted line become free, and at contact c<4> removes the short-circuit across winding 2 of relay F, so that it operates and connects up busy tone over contacts f4, c1. In the case of a dead number call, relay H energizes as in a call to an idle line, and connects up relay D, which is caused to operate by the presence of a loop, battery on the b wire or earth on the a wire, and so prevent the energization of relay S at contact d3. Relays G, F do not therefore operate, preventing metering or the sending of a busy signal. If desired, however, a special signal may be sent over the a or b wire. Release is under the control of the calling party, and the release magnet MM is connected up in the usual manner upon relapse of relays A, B. If the called party hangs up first, relay D falls back and lights a lamp 10, and an alarm may be operated through a pilot relay if this condition lasts a certain time. A pilot relay may also be inserted in series with the release magnet to give an alarm if the connector shaft sticks. Second arrangement, Fig. 2. Line relay A is connected up as in Fig. 1 and test relay H operates if the wanted line is free and short-circuits its high-resistance winding to mark the line engaged. Ringing relay S, which is slow to release, energizes over contacts f2, g1 when relay G relapses, and the incoming test wire is now earthed at contact f1 instead of at contact s1. Ring cutoff relay F energizes on the. reply of the called subscriber, short-circuits relay S and applies booster battery to the test wire to effect metering. Relay S falls back after an interval, connecting the calling and called lines and disconnecting booster battery. If the wanted line is busy, relay S energizes as before and connects up busy tone at contact s4. In the case of a dead number call, metering is prevented by an earth connection on the a wire, which short-circuits relays over contacts f2, s2, h2 (relay H operating as for an idle line).