Patent GB-238477-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1924-05-16
Abstract: 238,477. Automatic Telephone Manufacturing Co., Ltd., and Ostline, J. E. May 16, 1924. Automatic and semi-automatic exchange systems.-Relates to means for transmitting both audible busy signals and busy flash signals from group selectors and connectors, and to repeaters for repeating both signals, so that in a mixed network proper supervision is provided for calls from both automatic subscribers and from manual operators' positions. The busy flash currents are relayed at the repeater by intermittently completing a shortcircuit path for the current flowing normally over the speaking leads in series, this being effected by connecting earth and battery alternately to one speaking lead. The invention is described as applied to a mixed network of automatic and manual exchanges, in which, for example, a connection from an automatic subscriber or from a manual operator's position to an automatic subscriber A<1>, Fig 3, in an automatic exchange reached through another automatic exchange, is set up over a group selector S, Fig. 1, a repeater R', an exchange selector S<11>, Fig. 2, and a connector FS, Fig. 3. Means are also described for transmitting a busy tone and flash current when all the trunks in a wanted level of a group selector are busy. Group selector S, Fig. 1. This operates in known manner to select an idle trunk 700 - - 702 in a selected level with the exception that the change-over relay 505 is rendered slowto-release by providing it with a second winding adapted to be short-circuited by the stepping relay 506. If all the trunks in a selected level are engaged, cam springs 533 - - 535 are operated on the eleventh step, and an intermittent earth on the common lead IT causes the intermittent energization of relay 505, which now functions as a quick-acting relay, since its lower winding is not short-circuited at this time, and at armature 516 connects audible busy tone and earth from the common lead BT to the upper speaking conductor 501. The intermittent earth short-circuits a relay in the operator's cord circuit and causes a supervisory lamp to flash. Repeater R<1>, Fig. 2. The line relay 703 closes parallel circuits for relay 704, 707, and connects relay 705 across the outgoing trunk in series with the right-hand winding of a polarized relay 708, which does not respond since its left-hand winding is energized in opposition. Relay 705 opens the circuit of slow relav 707 before this has time to respond, whilst relay 704 earths the holding wire 701. The line relay 703 at armature 713 repeats the subsequent digits to the exchange selector S<11> (which operates in a similar manner to the selector S) and to the connector FS, Fig. 3, the slow-release relay 706 energizing on the first impulse and providing a direct bridge across the trunk 714, 715. If all the trunks in the wanted group outgoing from the selector S<11> are busy, alternate audible busy tone and flashing earth are connected to the conductor 714. The flashing earth on the conductor 714 intermittently shortcircuits relay 705, which closes a circuit for relay 707, which locks up and at armature 725 prepares a circuit for intermittently earthing the upper conductor 700. At each subsequent response of relay 705, when earth is removed from the conductor 714. the conductor 700 is earthed over a circuit 709, 720, 726, 725. The relays. 709 - - 711 ensure that earth is removed from the conductor 720 after a definite time interval determined by the slow-to-pull-up dash-pot relay 711. During the transmission of the busy signal the line relay 703 is held over circuit 720, 726, 725 and prevents release. This circuit is dependent upon the energization of relay 705 so that the connection is not permanently held up if an open trunk is seized. Connector FS, Fig. 3. This operates in the usual manner with the exception that the changeover relay 546 energized in parallel with the vertical magnet 551, and the usual relay 549 energized in parallel with the rotary magnet 552, short-circuit their lower windings to render themselves slow-to-release. If the wanted line is busy, busy relay 548 locks up, and busy tone from the lead BT is sent over circuit 570, 569, r, 541. Alternate battery and earth are also connected tothe conductor 541 over the lead BF, causing the relay 705, Fig. 2, to be intermittently deprived' of current. The intermittent relapse of relay 705 causes a flashing current to be sent over conduetor 700 as described in the previous paragraph. The resistance r is included in the line circuit to prevent the connection of direct battery potential to the line conductor. The reversal of current over the trunk 539, 541 due to the energization of the 'back bridge relay 543 when the called party answers, may be utilized to operate a meter or a supervisory relay in the operator's cord circuit. Specification 233,007 is referred to.