Patent GB-556192-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1942-06-03
Abstract: 556,192. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., CHRISTIAN, D. A., and LONG, D. P. June 3, 1942, No. 7547. [Class 40 (iv)] The allotters for several groups of callfinders are provided with a common multiple connected to all the finders, and each allotter is restricted in the exercise of its functions to a particular group of finders by permanent markings to one of its banks. The arrangement facilitates an economical disposition of finders on standard racks, the panels of which accommodate ten switches, for varying calling rates. If, for example, the average calling rate is such as to require 23 finders per 200 lines, one may provide two groups of 20 finders and one group of 30 for 600 lines and assign the lines having the heaviest calling rates to the large group of finders, a rack thus containing 7 panels of finders and one panel of allotters. Moreover, a group of finders may, if necessary, be partly accommodated on one or more panels of an adjacent rack, use being made of some of the spare outlets of the allotters in excess of the 70 required for the finders on their own rack. Some of the finders of a group may be ungraded and others graded, or some may be directly connected to selectors while others are connected via secondary finders, the allotters being arranged to give preference to the ungraded or directly connected finders. Each group of 200 lines may be served by two allotters, one for each sub-group of 100 lines and each acting as a reserve for the other, or by three allotters, one for each sub-group and one acting as a reserve for the other two. When a call is made, relay S common to the sub-group connects up the allotter start relay ST and a test circuit is prepared over wipers A7, 8, the terminals of the latter corresponding to the finders of the group being grounded. The allotter hunts if necessary until test relay T operates followed by TA which connects up the line relay of the group selector and starts the allotted finder. Test relay P operates when the calling line is found followed by PA which connects up switching relay HA and shortcircuits ST in case another call is waiting. Relay TA falls back and the allotter advances to pre-select an idle finder, after which the release of PA frees start relay ST for operation on a fresh call. The allotter stops in position 1 (since PA is up) if no idle finder is found before that position is reached. If, in the course of its search in response to the operation of ST the allotter passes through position 1, relay LC pulls up and causes it to stop should it continue to its last position : it is re-started after a short interval by the opening of time-controlled contacts sp. Should ST remain operated for 6 seconds, time-controlled relays SA, ZA give an alarm and transfer the start circuit to another allotter, in which relay WS operates as well as ST to cause the allotted finder to hunt over a second set of wipers and to bring in the corresponding switching relay HB. As shown, the group selector when idle applies battery to wire pb and thence over contacts ha6, hb6 to wire p. If instead the selector applies battery to wire p, these contacts would be in the connection between wire p and bank A7. In the case of graded finders, that is, two or more finders in different groups connected to the same group selector, the wire pb is connected over chain contacts of the several switching relays to the common p wire. The graded finders are connected to later positions of the allotters, and the terminals in bank A8 are cross-connected to the last terminal, which becomes earthed when LC pulls up, to ensure that they are tested last. A jack J1 is provided for routining purposes, a call being simulated by the operation of relay S in series with RT and all the finders of the group being driven in succession to their last positions.