Patent GB-554137-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1941-12-18
Abstract: 554,137. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., OLIVER, S. H., and WRIGHT, D. Dec. 18, 1941, No. 16335. [Class 40 (iv)] In a system in which outgoing calls from a P.B.X. are established over special finders EFS in response to the dialling of O into a local link (not shown), and in which incoming calls are normally established under the control of an operator, arrangements are made whereby a call incoming over any one or more particular junctions such as MEJ at night can be answered at a particular substation associated therewith by means of connections such as those shown between terminals 11, 12 and 13, 14, a warning tone being given to the subscriber if he is busy. If necessary, a local connection is broken down. The circuits of the exchange link are brought to the night-service condition shown with the aid of a key (not shown). The response of AC to incoming ringing current in these conditions brings up RX to energize BR and start an S and Z pulse timing equipment. The S relay NS marks the junction calling in the bank AS5 of the allotters such as AS4 and operates a relay TC which causes the allotters to be controlled over their banks AS5 instead of the banks AS6 over which they select an idle junction for an outgoing call. If the line is busy, NS also, over terminals 11, 12, re-operates the line relay R and this causes the allotter to hunt for the calling junction, the finder of which is then set on the night service line by reason of the marking over r2, k4 which is extended when the vertical wiper reaches the proper level to the bank EFS4. When the line is found, HA operates and locks and a warning tone from 18 is applied to the line. The relays N-F of the various links are connected up in turn or otherwise arranged to guard against the simultaneous operation of two of them. If the parties in the local connection hang up, NF which has previously been short-circuited by the ground on the wiper EFS3 over contact k3 is able to pull up and energize H which cuts off the warning tone and energizes RR to ring the night service line over ring cut-off relay F and initiate the release of RX. If the line is idle initially, NF pulls up in series with K when it is first connected up. Otherwise the operations are the same as when the line is busy. In both cases NR is operated over the lower junction wire to hold RR after the relapse of RX unless the call is abandoned. When the night-service extension replies, F releases RR to complete the talking circuit. NR is released but an alternative circuit is made for BR by release relay B. Line relay A bridges the coil I across the junction to operate the ring cut-off relay in the distant exchange. NS, NF are released but K, HA are held until release of the connection, by H and BR. Forced release.-If the parties do not clear before NZ comes up, full earth over NZ1 shunts out the switching relay of the connector or finder to break down the local connection. NZ then drops out and further operations take place as if the parties had cleared voluntarily. Night service line junction busy.-In this case the warning tone is applied as before but since the exchange finder switching relay has different circuits, it is not shunted down by the connection of ground over NZ1. Specifications 462,910 and 554,136 are referred to.