Patent GB-247742-A (GB)
Title: Improvements in automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1925-02-17
Abstract: 247,742. Western Electric Co., Ltd., Lowry, L. P., and Gould, J. R. Feb. 17, 1925. Automatic and semi-automatic exchange systems.-In an arrangement for providing non- numerical selection in a group larger than the capacity of a single switch, two or more switches are arranged so that if the first one fails to find an idle line it stops on its final terminals to which are connected the wipers of the next switch, which then takes up the hunt. The invention is described as applied to the selection of one of a group of 96 lines to a private branch exchange, and the arrangement includes ringing and supervisory arrangements. The arrangement is designed to operate whether impulses continue to be received or not, but while they are coming in the talking wipers are disconnected. Selection of an idle line. Line relay A, release relay B and relay C pull when the device is seized. The magnet ROT1 moves the first switch out of normal in a circuit PI, B6, HI and over busy terminals in a circuit H1, B6, P1. If there are no idle lines from this switch, the wipers stop on the final terminals in which the wipers H1, P1 are disconnected from the magnet ROT1 and connected over wipers H2, P2 to the magnet ROT2 of the second switch which then takes up the hunt. Busy signal and statistical metering. If the wipers reach their final terminals, the circuit H2, HI, P1, P2 is transferred from the driving magnet to the lower winding of the ringing cut-off relay F, which completes a circuit for the meter M over +, F8, P1, P2, releases rleay C, and connects busy tone and flash from BF over a protective resistance to the incoming + wire. If impulses come in at this stage, relay C pulls up over its lower winding and disconnects the busy wire which might otherwise make relay A too sluggish to respond to impulses and so cause premature release. Control of ringing current and completion of connection. When an idle line is found, relay II which has hitherto been short-circuited over the test wiper, pulls up in series with the driving magnet, grounds the test wiper to operate the cut-off relay, disconnects relay C and completes the ring-back tone circuit. Relay C on falling back completes the ringing circuit over relay F. When the P.B.X. operator answers, relay Flocks up over its light armature 5 and completes the connection back to relay E which reverses the connections of the line relay for metering. If further impulses come in at this stage, relav C disconnects the talking wipers, but the relapse and re-energization of relay E do not affect the meter which is locked up. Release. When the calling party hangs up, relays A, B, H, F fall back and relay D pulls up and locks up relay C (which pulls up on the relapse of relay A) to hold the device busy at C12 until it is completely restored. A common release signalling relay is included in the locking circuit of relav C. The second switch, if off-normal, is then driven on to normal and then the first switch. Relay B is further disconnected bv relay D to prevent its operation if the subscriber calls again. The circuits for relay D and for the driving magnets depend on which switch has been used and on whether release follows conversation or the busy signal. The circuits are so arranged that restoration to normal takes place at whatever stage the connection is released.