Patent GB-276751-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1926-06-04
Abstract: 276,751. Siemens Bros. & Co., Ltd., and Dumjohn, F. P. W. June 4, 1926. Automatic exchange systems. - In a commoning arrangement in which the outlets from a number of shelves of selectors are grouped, the early choices in a level are connected directly to a common group of outgoing links whilst the later choices have access to these links over non-numerical switches. Fig. 2 shows the grading panel of one level of ten shelves of the group selectors, the horizontal rows A - - K representing the levels in the shelves and the vertical columns 1 - - 10 representing the ten choices. Forty outgoing links a are directly connected to the first five choices, the first three choices having individual access to outgoing links and choices. 4 and 5 having access to links common to two shelves. Choices 6 to 10 are graded to 20 preselectors PS having access to the links a. These preselectors are so arranged that as far as possible they do not give access to links that are directly accessible over the early choices of the levels to which they are alloted. In one arrangement using ten-point preselectors, groups of five are multipled together and connected to ten links, the five preselectors allotted to the 6th choice in shelves A - - E giving access to the links connected directly to choices 4 and 5 in all the shelves, those allotted to the 6th choice in shelves F - - K giving access to the links connected to choice 3 in all the shelves. those allotted to the 7th choice in all the shelves giving access to the links connected to choice 2, and so on. Other grading arrangements for the later choices are described, in some of which the last choices of the links to preselectors are connected individually to preselectors. An arrangement is also described in which the first five choices are individually connected to fifty outgoing links and the last five choices individually connected to fifty preselectors. The preselectors are preferably of the non-homing type and are so arranged that when a last (fifth) choice of direct links is taken into use all the preselectors, or the sub-group of preselectors associated with the indirect choices following that particular fifth choice, hunt for free outgoing links and continue to do so as links are seized. A selector can seize an outgoing link even though a preselector has tested in, and several preselectors may rest on the same idle link. Fig. 6 shows a connection a having direct means to an outgoing link OL and a connector b to a preselector PS having access to the link OL. If the link OL has not already been taken into use over a group selector, when a searching group selector GS<1> engages the early direct choice connection a, switching relay T energizes in series with a test relay N and earths the test wire, thereby energizing the starting relay R of any preselector standing on this link, which at the same time is marked busy by the response of relay N. The stepping magnet DM is now energized and interacts with the relay R until an idle link is engaged. As no busy marking is applied by a preselector two or more may rest on the same link. If all the outlets from the preselector are busy, a contact gp is open and hunting is prevented. Contact e is open if no fifth direct choice has been seized in any shelf, so that if a preselector in hunting arrives on its normal contacts it stops there since it finds no earth connection, but when a fifth choice is taken up, a relay such as N closes the contact e and the preselector hunts for an idle link. A group selector such as GS<2>. unable to find an idle direct link in the earlier choices, continues its search over the later choices, testing in over relay P, wiper D and winding 1 of relay R. Relay TT connects earth to the test wire which is extended over contact p<1> to mark the link OL busy in its early choice : relay N energizes and connects up its high-resistance winding. If all the choices are busy the group selector may advance to 11th contacts where a busy signal is given.