Patent GB-360983-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1930-08-16
Abstract: 360,983. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, Liverpool, and BAKER, G. T., Blackbrook, Caerphilly, Glamorgan. Aug. 16, 1930, No. 24601. [Class 40 (iv).] In a district office system, a discriminating selector, which responds to the first two digits of the wanted number to determine whether a local or a main exchange call is required, in the event of a main exchange call remains in the position to which it has been set and controls zone metering, while in the event of a local call it restores and serves as the group selector in the local connection. An associated line switch gives access to the main exchange junctions. Main exchange calls. The discriminating selector is connected to the calling line over a finder switch, and line and release relays A, B operate, completing initial circuits for relays C, E. Relay J energizes in parallel with relay C, locks and starts the operation of the line switch OGS in search of an idle junction. Switching relay K completes the circuit to the main exchange, from which dialling tone is sent back. The first train of impulses are repeated to the vertical magnet VM and series relay C, which on falling back connects in the rotary magnet RM and series relay E to receive the second train of impulses. Both these impulse trains are repeated over the junction, relays D, I being short-circuited in the usual manner. A false impulse prior to dialling may be absorbed by the operation of the release magnet ZM over vertical wiper VW, the initial digit 1 not being used. Assuming that the setting of the discriminating selector denotes a main exchange call, the remaining digits are repeated over the junction to complete the connection. The terminals of wiper P1 are connected in multiple to the appropriate zone metering wires, and when relay D energizes on the called party's reply, delayed metering relays DA, DB operate through the medium of time pulse cams S, Z to place the metering circuit 12 for a period under the control of relay MR, which operates over wiper P1 a number of times dependent on the setting of the selector, relay J being held over cam Z during each operation of relay MR. Relay DB locks and remains held during conversation. Local calls. The terminals of wiper PI denoting local calls are wired in multiple to relay L, which energizes and locks when relay E falls back, and connects up the release magnet ZM to restore the selector. Relay J is released and in turn disconnects relay K to release the junction. Relays C, E re-energize and connect up relay ML. The vertical magnet VM responds to the third digit of the local number, and relay C on falling back closes an initial circuit for the rotary magnet RM which, due to the operation of relays L,ML, now interacts with relay G to step the selector until an idle trunk is found, when switching relay H energizes to extend the connection to the next switching stage. If all the trunks are engaged, eleventh step springs S are operated and a busy tone is sent back. When relay D energizes on the called party's reply, delayed metering relays DA, DB operate to effect metering as described above, relay MR being now connected to the single metering wire 14 by the operation of relay ML. Unobtainable numbers. The spare terminals of wiper P1 are connected to battery. Relay MR accordingly operates continuously and releases relay J, which connects up NU tone and disconnects relay K to release the junction. All junctions engaged. Relay K energizes in the last position of the switch OGS, and dialling tone is connected up locally. The discriminating selector responds to the first two dialled digits, and if these denote a main exchange call, busy tone is sent back when relay E falls back. Calls to an operator. If the calling subscriber dials O, relay ML energizes over vertical wiper VW, and the circuit for relay E is opened, so that further impulses are ineffective. The incoming selector at the main exchange gives access to an operator over its tenth level. Guarding the junction during release. Each junction is provided with relays JA, JB connected to the test terminal. The junction is held at the outgoing end during the successive release of three sluggish relays B, J, JB to ensure release of the main exchange switches. Specifications 339,345 and 339,600, [both in Class 40 (iv), Telephones &c.], are referred to.