Patent GB-481671-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/58
Filed: 1936-09-15
Abstract: 481,671. Automatic exchange systems. ERICSSON TELEPHONES, Ltd., and DRYSDALE, L. H. Sept. 15, 1936, No. 25113. [Class 40 (iv)] A two-directional switch of the kind in which release is effected by a continuation of the rotary movement to the end of the bank is employed for digit absorption and in order to provide the minimum time for release between two successive digits is stepped automatically to the first level on seizure and absorbs the first digit by rotary movement over the first level. Lines leading to an operator's position may be connected to this level the switch after responding to digit 0 being released and then again stepped automatically to the first level over which it hunts. The invention is described as applied to a district - office discriminating selector which absorbs the first digit for local calls. In the drawing, the bank associated with wiper ls3 shows all the connections on the first level and the contacts FC show the connections to the first contacts on the remaining levels. Local call. Relays A, B, BA, J, operate on seizure and contact ba1 causes the vertical magnet LSV to raise the wipers to the first level. At the same time, an auxiliary switch jh1 .. 4 hunts for a free junction to the main exchange and when this is found relay K operates and connects up dialling tone DT. The first digit is repeated by relay A to the rotary magnet LSR and on the relapse of relay C at the end of the digit, ground is connected to wiper ls3 over a front contact of relay JG which was energized by relay C at the first impulse. If the digit denotes a possible local call (5) relay DA operates completing a self - stepping circuit for magnet LSR to restore the switch, and relay OA then operates and releases DA. Relay H also operates. The second digit (7, 8 or 9 for a local call) is repeated to the vertical magnet LSV and on the relapse of relay C, the rotary magnet LSR steps the wipers to the first contacts in the selected level and relay LD operates releasing relays K, JG, and the junction. If the outlet connected to the first contacts is busy relay H remains operated over its right-hand winding, and the rotary magnet continues to operate by self-interruption until relay H releases on an idle outlet being found. If all outlets are busy contacts s1 . . s3 operate at the eleventh step and connect up busy tone BT. Call to main exchange. For a number with first digit 5 and second digit other than 7, 8 or 9, the switch operates as for a local call, but relay JD operates over the first contacts in the selected level and wiper ls3 disconnecting the switch stepping circuit so that the switch remains set and further digits pass only to the main exchange. For a first digit other than 5 or 0, relay JD operates over the appropriate contact in the first level of wiper Ls3. If all junctions are busy, relay OF operates at the end of the bank of switch jh1 .. 4 and connects up busy tone. Call to operator. In response to digit 0, the switch steps rotarily over the first level as before and at the end of the digit relays DA, MB operate over wiper Ls3. Relay DA releases the switch as before, relay OA operates and energizes H, and relays MB, H then complete a circuit for the vertical magnet LSV which again steps the switch to the first level over which hunting proceeds as for a local call, relay LD being operated by relays MB, OA. Faulty working ; provision of rectifier MRA. Metering is effected by the connection of positive battery to the incoming test wire 3 by relay MD when the called subscriber replies and if this battery fails the busy condition is maintained on wire 3 over a rectifier MRA.