GB542455A - Improvements relating to telephone systems - Google Patents

Abstract

542,455. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and CLAY, D. L. Sept. 30, 1940, No. 14720. [Class 40 (iv)] A privileged subscriber who is leaving his telephone or who does not wish to be disturbed may set apparatus associated with his line at the exchange (1) to direct incoming calls to the line of another subscriber, (2) to give a distinctive tone or announcement to a caller who may then by further dialling complete the call to the privileged subscriber's own line or to another line, or (3) to give NU tone. The arrangement does not interfere with the use of the line for outgoing calls. The apparatus is connected to the final selector outlets allotted to the privileged subscriber's number and includes a rotary switch RR giving access to his line and to other lines to which calls may be transferred. For the purpose of setting the apparatus, it may be reached by dialling a special number from any substation, whereupon the switch RR may be controlled by a further train of impulses. If the privileged subscriber is situated near the exchange however, the switch RR may be controlled by marking relays operated from a set of keys. Assuming that the apparatus is seized in response to a special number, line relay A energizes over a preceding loop, the switch RR if off-normal goes home, and dialling tone is returned. Impulses are repeated by A to step the switch RR and to operate relays P, Q in turn, the arrangement being such that relay Q remains up when the switch is set to an odd position. With the switch in an even position, an incoming call is extended directly either to the privileged subscriber's line in position 0 (normal), to another line in position 2, 4, 6 or 8, or to a source of NU tone in position 10. The odd positions are wired to the same lines, but since relay Q is up, an incoming call energizes line relay AA and a distinctive tone is given over wire RT. If the caller decides to persist in the call, the dialling of any digit results in the operation of relays E, ON, whereupon the line is tested by relay H and ringing or busy signalling takes place in the usual manner, switching being performed by ring-trip relay TR upon reply. The apparatus may be modified so that all calls or all except those extended over the normal position of the switch are held in suspense by connecting the final selector outlets directly to relay AA or over make contacts of an off-normal relay. The allocation of two positions of the switch to each line is then unnecessary. The apparatus can be added at an existing exchange by means of connections at the intermediate distributing frame.