Patent GB-351550-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-03-27
Abstract: 351,550. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, and BELAS, F. T., 24, Stanley Street, both in Liverpool. March 27, 1930, No. 9849. [Class 40 (iv).] Final selectors employed in establishing both local and toll connections have two sets of wipers which are used alternatively for local and toll calls, discrimination being effected by a differential relay which energizes when the switch is taken into use by an operator. The corresponding banks are connected to the same subscribers' lines, and the line circuits are modified to enable an operator to break down a local connection. An operator may also set up toll connections at another exchange, a suitable repeater being associated with the interexchange junction. The system described employs bi-directional finder switches of the kind described in Specification 333,182, [Class 40 (iv), Telephones &c.]. Specification 351,549 also is referred to. Line equipment, Figs. 1 and 1A. Line relay LR remains energized during conversation over its lower winding in series with cut-off relay CO. Relay BD, Fig. 1, is adapted to disconnect the subscriber from a local connection. This relay is dispensed with in Fig. 1A and battery over wiper 6d, Fig. 4, short-circuits and releases line relay LR, which disconnects the subscribers' line. Failure to dial. Release relay 2B of the group selector, Fig. 3, connects up relay SP, Fig. 2, which locks and prepares a circuit for relay ZP. A motor start relay also energizes, connecting up relay ST, Fig. 9. Time pulses applied to wire 17 now step the rotary switch DAR until the position corresponding to the finder, Fig. 2, is reached, when relay ZP energizes over wire 18 and disconnects switching relay H, and line relay LR, Fig. 1. Cut-off relay CO remains held over the calling loop, lighting lamp LP and connecting up relay LA, Fig. 8, to give an alarm signal. The subscribers' line is marked busy in the final selector banks by ground applied through the loop and over relay LR. Local group selector, Fig. 3. This is of well-known type, except that it is adapted to absorb the first digit when it has a particular value by the provision of post springs NP1, NP2 which operate on the corresponding level. Relay 2G which normally initiates the rotary movement then releases, and when dialling relay 2C relapses, a circuit is closed for the release magnet 2ZM to restore the switch. In the normal position, relay F energizes and locks to enable the switch to respond to the next digit. Final selector, Fig. 4. Local call. Line relay 3A energizes, but relay AA in series therewith is inoperative since its windings are in opposition. Release relay 3B pulls up, and the vertical and rotary magnets 3VM, 3RM respond to the last two digits, relays 3C, E being energized during the trains. If the wanted line is engaged, busy relay 3G energizes to ground on test wiper 3d before relay E relapses, and connects up busy tone from wire 40. If test wiper 3d is connected to a high-resistance ground, relay 3G operates only first its light armature 3g1 and operates fully over a local circuit when relay E relapses. If the wanted line is idle, switching relay 2H energizes when relay E relapses, locks, connects up ringing current from wire 42 through ring-trip relay F and applies full ground to test wiper 3d from contact dr3. Upon reply, ring-trip relay F energizes, followed by backbridge relay D. Release. If the calling party hangs up first, relays 3A, 3B fall back and relay E energizes momentarily to remove ground from the test wire 37 at contact e4 to release the preceding switch. Failure of either party to hang up is indicated by the lighting of supervisory lamp 1LP in series with relay 1LA, Fig. 10, which connects up relay 4A. Relay 1ST energizes, and the rotary switch DBR steps under control of time pulses on wire 17. After 20 steps, equivalent to a delay of three minutes, relay 4B energizes, disconnects relay 4A and locks in series with group supervisory lamp 2LP. Main supervisory lamp 3LP also lights, and relay 1ST falls back and restores the switch DBR. Final selector, Fig. 4. Toll call. Connection is made from the toll operator's position, Fig. 8, to the final selector, Fig. 4, through a jack IK and a toll group selector of well-known type. Ring and dial key RDK being operated, both trunk wires are grounded, and consequently differential relay AA energizes in series with line relay 3A. Relays AD, DR pull up, and the latter locks. The vertical and rotary magnets 3VM, 3RM operate as in the case of a local call, except that relay 3C re-energizes during the rotary motion. If the wanted line is idle, the call is completed as before, except that wiper 3d is grounded through a resistance 7B instead of directly to mark the line toll busy. If the wanted line is engaged in a toll call, busy relay 3G energizes, and in the interval between the relapse of relays E, 3C, a circuit is closed through the upper winding of relay 2TB to parallel batteries through relay 3G and through line and cut-off relays LR, CO of the wanted line. Relay 2TB energizes, locks over both windings and disconnects relay 3G, whereupon toll busy tone is connected to the incoming trunk at wire 47. If on the other hand the wanted line is engaged in a local call, busy relay 3G energizes as before, but relay 2TB is inoperative since its upper winding is shortcircuited by direct ground on wiper 3d. Two-step relay TS energizes fully when key RDK, Fig. 8, is restored, owing to the relapse of relays AA, AD, and when relay 3C falls back a " cut-in " connection is completed to the wanted subscriber over wipers 1d, 2d. Back-bridge relay D energizes in a local circuit to provide for supervision. The operator asks both parties in the local call to hang up, whereupon the removal of ground from wiper 3d releases relay 3G and the call is completed as if the wanted line had been idle. If necessary however the operator may break down the local connection by depressing break-down key BDK, Fig. 8, 'to ground both trunk wires. Relays AA, AD respond, and two-step relay TD energizes fully when key BDK is restored, allowing relay M, which was previously short-circuited, to energize in series with the rotary magnet 3RM and lock over wiper 3d. Relay TD also switches the speaking wires from wipers 1d, 2d to wipers 4d, 5d, trips ring-trip relay IF and connects battery through a resistance YC to wiper 6d to energize break-down relay BD, Fig. 1, or to release line relay LR, Fig. 1a, thus disconnecting the wanted line from the local connection. Switching relay 2H energizes and locks to complete the toll connection. The operator may recall the subscriber by again depressing breakdown key BDK, whereupon relays AA, AD respond and connect continuous ringing tone from wire 51 to the line. If the calling party hangs up first, release relay 3B on falling back grounds wiper 3d directly to enable another toll operator to " cut-in " if necessary. After a local connection has been broken down, should the same subscriber be wanted in a second toll call, wiper 3d may find direct ground still applied from the final selector in the local connection, thus preventing the normal operation of relay 2TB. After relay TS pulls up however due to the restoration of key RDK, a circuit for relay 2TB is completed over wiper 6d to battery in the other toll final selector. Inter-exchange calls. The toll group selector has access over certain levels to outgoing repeaters, Fig. 7, which are arranged to repeat the connection of ground to both speaking wires to enable the operator to break down local calls at the distant exchange. Differential relay 1AA in series with line relay 6A upon energization connects up relay 1AD, which applies ground through a resistance to both junction wires. Dialling relay 5C ensures a low-resistance impulsing loop in the usual manner. Unobtainable numbers. Spare positions in the group and final selector banks are connected to relays which effect the transmission of NU tone.