Patent GB-153168-A (GB)
IPC: H04M7/10
Abstract: 153,168. Lenaghan, T. April 23, 1919. Automatic and semi-automatic exchange systems.-A trunk circuit 6, Fig. 1, is connectible to a number of incoming lines a, b, c, d, terminating in line finders 1<a>, 1<b>, &c., and to a number of numerically different outgoing lines A<1>, B<1>, C<1>, &c., terminating in group selectors serving different areas. When a part of the trunk 6 has been appropriated for establishing a connexion, the rest of the trunk remains available for establishing other connexions, but while the first user of the trunk can obtain access to any of the outgoing lines, subsequent users are subject to restrictions. For example, if a call has been extended from line b to line D' over the part of the trunk marked bd (contact 11 having been moved downward, contact 12 to the left, and contact 13 to the right) a subsequent call on line a could only be extended in the directions A<1>, E<1>, F<1>. G<1>, H<1>, and not in the directions B<1>, C<1>, D<1>. The line finders of all available common trunks 6 are started to find a calling line, but a finder is only stopped on the calling line if the trunk 6 to which it gives access is capable of extending the call in the desired direction. The trunk 6, which is represented in the skeleton diagram by a single line, consists in practice of a group of five wires, and the contacts of each of the sets A, B, C, &c. for connecting it to different outgoing lines are divided in practice among a group of relays situated at the junction of.the trunk and out-going line. The invention is described in its application to a. system of the kind disclosed in Specification 152,702, in which the digits of the wanted number are recorded on a register-controller in terms of varying polarity and resistance. It will be assumed that a connexion is to be extended from a calling line 100 in the direction A<1>. For the first digit, which controls the extension of the call through a common trunk such as 6, the effect of the register is as follows :-(1) Positive potential is applied to the calling subscriber's T terminals in the banks of the finders 1<a>, and when a finder arrives at the calling line a polarized relay is operated with an effect represented by the downward movement of the contact 14. (If the call were to be extended in a direction E<1>, F<1>, G<1>, or H<1> the register would apply negative potential to the same circuit and the effect of the polarized relay would be equivalent to an upward movement of contact 14). (2) Positive potential is applied to the subscriber's R terminal, energizing a polarized relay which has an effect equivalent to the movement of contact 15 to the right and contact 16 to the left, completing the connexion of line a to line A<1>. (If the call were to be extended in the direction B<1>, the register would apply negative potential to the same circuit; in this case the polarized relay would move contact 16 to the left, but would not operate contact 15, and another polarized relay, belonging to the set B, would move contact 17 to the right, completing the connexion of line a to line B<1>. If the call were to be extended in the direction C<1> or D<1>, negative or positive potential would be applied to the subscriber's L terminal, the contact 15 being moved to the left, to extend the call in the other direction along the trunk 6.) Operations (1) and (2) take place successively in the moment during which the finder is moving over the terminals of the calling line, and the finder is arrested by a current which results from the successful operation of the trunk relays. If, for reasons explained earlier in this abridgement, the trunk 6 is incapable of extending the call in the desired direction, the trunk circuits will not be in a condition to send an arresting current to the finder. and connexion will be made through the next finder that reaches the calling line, provided that the trunk 6 with which it is associated is not similarly incapacitated.