Patent GB-216087-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1923-10-30
Abstract: 216,087. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Bellamy, J. I., and Gardner, J. E.). May 17, 1923, [Convention date]. Automatic and semi-automatic exchange systems.-In systems in which a hunting switch such as a group selector gives access to outgoing trunks over a secondary, non-numerical switch, the latter is of call-finder type, and pre-selects an idle link 'between its terminals and those of the group selector. Fig. 1 shows the connections of 250 primary trunks divided into 25 sub-groups PSG.1 - - PSG.25 with the banks of 150 finders F each of which is associated with a trunk to a distant office. The finders are divided into subgroups of 15, one in each sub-group being shown. One trunk of each primary sub-group goes to each secondary sub-group, the first primary sub-group accounting for the first terminals of all the finders, the second for the second, and so on. The finders are so controlled that two idle trunks in each primary sub-group are always associated with two outgoing trunks and the remaining trunks in the sub-group, even if idle, are marked busy to the group-selectors giving access to them. Pre-selecting two idle trunks. It is assumed that the trunks T-1-T-10 have just been added to the office and that the current has just been switched on. Relay 101, Fig. 3, energizes over contact 113 and a chain of similar contacts in the trunk circuits TC-1 - - TC-10 of the sub-group. Relay 101 removes ground from the test terminals such as 139 of the trunks T-1 - - T-10 in all the finders and grounds the start wire 130 energizing the relay 154 of the first idle finder F-1 in the first secondary sub-group. Relay 154 connects the switching relay 153 in series with the stepping magnet 151, and the junction point to the test wiper 142. If now the wipers 141 - - 143 are on the trunk of a primary sub-group in which two trunks are not already pre-selected, switching relay 153 energizes immediately. It is assumed, however, that this is not the case, and the finder F-1 accordingly hunts in the usual manner for the ungrounded terminal 189. Relay 153 on energizing releases relay 154 and extends the start wire over 165 to the next idle finder in the same secondary sub-group. The switching through of the talking wires energizes relay 110 in series with relay 171 which does not energize at this stage. Relay 110 grounds terminal 139 to lock up relay 153, ungrounds wire 68 to make the trunk T-1 selectable by a group selector, switches over the start-wire 130 to the second trunk circuit and second sub-group finders (not shown), and removes the shunt round resistance 12. A finder in the second secondary subgroup now selects the trunk T-2 in a similar manner, and when the shunt round a second resistance such as 112 is removed, relay 101 falls back, re-grounds wire 104: to make the remaining trunks inaccessible to the finders and de-energizes the start wire. Extension of a call and release. When a group selector D operating in the usual manner seizes the pre-seleoted trunk T-1, relay 111 pulls up, locks itself to the wire 68 which it extends to the wire 167 and releases relay 110. Relay 171 energizes over the loop, energizes relay 172 and repeats the next digit over the outgoing trunk. Relay 172 returns ground to hold up relays 153, 111 and the preceding selectors, and when this ground is removed at the end of the call these are all released. When relay 110 releases on the energization of relay 111, the resistance 112 is again shunted and relay 101 energizes and grounds the wire 130 which is now connected to the trunk circuit of the third trunk. A finder of the third secondary sub-group accordingly hunts for trunk T-3 and relay 101 again relapses. When, on the release of the connection relay 111 falls back the start wire 130 is again connected to the finders of the first secondary sub-group, and when relay 101 next energizes the trunk T-1 is selected by one of these. Operation when all the switches of a secondary sub-group are busy. Fig. 4 shows the 25 starting circuits such as SC-1 of the first secondary sub-group. The chain circuit to the right of the Figure ;is a well-known arrangement whereby when any starting circuit is completed the nearest idle finder to that circuit is started. When all the switches of a sub-group are busy a chain circuit for relay 169 is completed and all the starting circuits are extended back to their own trunk circuits so that an idle finder can be started in another sub-group. For example, the trunk T-1 is idle, but the first secondary sub-group is busy. Relay 169 accordingly is energized. Relay 101 energizes to cause the pre-selection of another trunk in the first primary sub-group. The wire 130 is now connected over a contact of relay 169 to the wire 132 and a finder is therefore started in another sub-group to select an idle-trunk other than T-1. Statistical metering. If the relay 101 energizes when the trunks T-1 - - T-10 are all either in use, pre-selected or unavailable because their associated secondary sub-groups are busy, the starting ground at 102 is extended to the meter M, individual to this primary sub-group. It will be noted that this meter operates when there is still one idle trunk in the sub-group available for extending a call. Specifications 169,698, 191,055 and 195,928 are referred to.