Patent GB-466889-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1935-12-07
Abstract: 466,889. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., BEALE, C. E., and RICHARDS, 1. T. Dec. 7, 1935, No. 33973. [Class 40 (iv)] In a satellite exchange in which a hunting switch normally selects an idle junction to the main exchange from which dialling tone is then supplied, if all junctions are busy a relay operated in the last position of the hunting switch connects up a local source of dialling tone and prepares a circuit for connecting up busy tone if a main-exchange number is dialled. In the circuit shown, three double-purpose relays are provided, one (CJ) serving to improve the junction impulsing circuit during dialling and to transmit booster metering impulses, the second (DB) serving to initiate delayed metering and to provide operator-hold conditions for a toll call, whilst the third (JB) controls the local dialling-and busy-tone circuits as referred to above and also responds to signals from a toll operator to re-ring the calling subscriber. Local call. Relays A, B, E, C operate, and switch JH hunts for an idle junction to the main exchange. The first digit is repeated to the vertical magnet VM and over the junction. When the discriminator switch moves off normal, the left-hand winding of C is shortcircuited rendering the relay sluggish and causing it to release at the end of the digit so that the second digit passes to the rotary magnet RM through the upper winding of E. On the relapse of E, relay LD, for a local call, operates over wiper P1, releasing the junction and completing a circuit for the vertical magnet so that the discriminator is released over the setting path in a manner similar to that described in Specification 391,151. Relays C, E then re-operate and relay ML is energized. During the receipt of the third digit relay H operates over contacts N1 and magnet JHM and at the end of the digit a self-interrupting circuit is closed for the rotary magnet RM. When an idle outlet is found relay H, being no longer locked over its right-hand winding and the test wiper, releases and relay C re-operates disconnecting the rotary magnet and reenergizing H to switch through. Main-exchange call. Relay LD is not operated and further digits are repeated to the main exchange. If no junction is available, relay JB operates in the last position of switch JH and connects up local dialling tone DT, and if the first two digits denote a main-exchange call busy tone BT is transmitted via the middle winding of relay A. Metering. For local calls, relay ML connects up the single-metering lead 11, whilst for main-exchange calls multi-metering takes place in accordance with connections to bank P1. When the called subscriber replies, relay D operates connecting up the cam-controlled delay relays DA, DB, and relay CJ is operated to transmit the desired number of metering impulses as booster impulses over the incoming test wire. Toll call. In response to digit 0, postsprings NP1 operate relay TD which releases the ordinary junction and connects relays OA, JB to the speaking wires. Relay ML also operates and hunting for a special high-grade junction proceeds over the tenth level as in a local call. Ring-back tone RBT is sent back to the calling subscriber until the operator plugs in when relays OA, DB operate. If the calling subscriber hangs up, relays A, OA release and JB is connected to the outgoing positive wire but does not operate owing to the shunt rectifier MRA. The calling subscriber is re-rung by the operator connecting booster battery to the positive wire causing relay JB to operate and connect up ringing generator GNR. Release. When the calling subscriber hangs up, the incoming test wire is freed to release preceding apparatus for a time equal to the sum of the release times of relays ML, C, H for a local call and to the release time of relay C for a main-exchange call.