Patent GB-191422715-A (GB)
Title: Improvements in Automatic and Semi-automatic Telephone Systems.
Filed: 1914-11-18
Granted: 1915-11-18
Abstract: 22,715. Relay Automatic Telephone Co., [formerly Betulander Automatic Telephone Co.], and Aitken, W. Nov. 18. Automatic and semi-automatic exchange systems. - Outgoing lines are divided into a number of groups of first-choice lines, each group individual to a particular group of incoming lines, and a group of second-choice lines common to all the groups of incoming lines, the arrangements being such that a second-choice line can only be taken into use when no firstchoice line is available. The application of the same method to manual systems is described in Specification 20,453/14. the second-choice lines carry the peak loads of the various groups. They may themselves be divided into two groups, of which one is broached only when the other is fully engaged. The different groups of incoming lines may have first access to different lines in the common second-choice outgoing group. The method is applicable to the callfinder or other non-numerical part of the switching system, but is described in its application to the groups of lines between the first and second group selectors of an exchange. In each level of the first selectors, there are a number of first-choice outgoing lines individual to a group of first selectors, and a number of secondchoice lines common to several groups of first selectors. This is expressed in terms of mechanical switches; but the arrangements shown in Fig 4 are based on the use of relay sets as selectors. When a call arrives on the line I, the relays LR and RR1 are energized and complete the circuit of a relay L. The line interruptions representing the first digit are repeated by the relay LR to the impulse-counting relay set St, each impulse energizing a pair of relays H, M; I, N, &c. and unlocking the upper relay of the previous pair. Also, as long as impulses are passing, a slow-release relay RR2 is energized. When the impulses terminate (in the present instance it is assumed that there is only a single impulse), the relay RR., deenergizes and completes the circuits of the cut-off relay CO and of a relay S (individual to the selected outgoing group), which brings into action a relay set A1. This relay set serves to select an idle line in the first-choice division of the selected group. The relays AR1, AR2, &c, of the set Al are connected by the relay C, to the test-wires TW1 of this set of lines. The relays corresponding to busy lines are energized, and the energized relays ground a particular combination of a set of code wires CW, which control self-locking relays T, U, V, &c., which operate in combination to extend the calling line to an idle first-choice line (such as J1) of the wanted group. The ground connexion of the test circuit of the selected line energizes the relay CR1, which cuts out the relay S and releases the assignor Al. If all the first-choice lines are already engaged, the relays AR1, AR2, &c. are all energized, and a circuit is completed for the relay C2 of a second assignor A2, the relays of which are connected to the testwires TW2 of the second-choice lines. The assignor A2 in this case controls the relays T, U. V, &c. over the code wires CW in such a way as to select an idle second-choice line (such as JÎ) of the wanted group. Meters M1, M2 serve to count the number of occasions on which all the first-choice lines, and all the secondchoice lines, respectively, are engaged.