Patent GB-227888-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1923-09-18
Abstract: 227,888. Automatic Telephone Manufacturing Co., Ltd., Mercer, R., and Tench, r. Sept. 18, 1923. Automatic exchange systems.-In order to obtain the benefit of large groups, certain switches in response to different values of digit give access to the same main group of trunks. For example, in a networkof only a few exchanges, the trunks from three of the levels of a first selector may all go to the same exchange. In order that the main group may be of the most suitable size, grading may be employed between levels. As shown, for example, in Fig. 9, all the trunks from levels 2 - - 4 go in the same direction, the first five on each level being individual to that level and the remainder common to all three levels. The ten trunks reached in response to a particular digit are called a sub.group. Where necessary, a, discriminating potential is repeated along the line of switches to effect wiper selection in (say) a double wiper connector, in accordance with the sub-group over which the call was made. A further development is shown in Fig. 1 in which all the selectors are of double-wiper type. The trunks from levels 1 and 6, 2 and 7, &c. in each of the banks of the first selector D lead in the same direction, as denoted by the open circles joining these levels. The trunks from corresponding pairs of levels in the two banks are brought together and may be continued as two subgroups of a main group or may be multipled to form a single group as indicated by the circle enclosing a cross. In the latter case the selector in response to a digit either 1 or 6 hunts through the same twenty trunks. The second selector is of known simultaneous-hunting type and the connector is of double wiper type, selection of a particular set being in accordance with the first digit. In a modification this wiper-selection is effected at the second selector and the connectors are standard and in a further modification the first selector is standard and the second is like selector D, Fig. 1. In a further system, Fig. 4, the first selector D3 is moved only by odd digits, as described in Specification 134,812, and is arranged for simultaneous hunting in levels 1 and 6, 2 and 7, &c. The even digits control the forwarding of a discriminating impulse to effect wiper selection in the connector H4. In a 5000-line system the first selector terminals may be arranged as in selector D3, but the selector takes a step at each impulse. In this case no discrimination is necessary. In a system of only 5000 lines but using all first digits, it is arranged that all numbers with odd first digits have odd last digits, and that all those with even first digits have even last digits. In this case all the selectors are standard single-wiper switches but the levels of the first selector are graded in pairs throughout the bank. No discrimination is necessary. The system shown in Fig. 1 is described in detail. Construction of switches. When a selector liable to be given ten steps and having only ten levels is arranged for simultaneous hunting in two levels five steps apart, three wiper sets are provided at intervals of five steps, the upper and lower sets being connected together and acting as one set. First selector, Fig. 6. This is a double-wiper simultaneous-hunting Strowger switch of which the controlling circuits are substantially identical with those described in Specification 170,385. On five levels, however (e.g. if the first digit is greater than 5) post springs 38 operate so that ground is connected to the lower talking wire in the interval between the energization of one of the switching relays 26, 27 and the relapse of the release relav 6. Second selector, Fig. 7. This is controlled similarly to the first selector but line relay 45 first energizes over its upper winding only. In the absence of a discriminating impulse the line relay energizes in series with relay 49 which locks up and opens the circuit for repeating the impulse. Otherwise, relay 49 is short-circuited, and since it is disconnected when the release relay 46 pulls up, cannot pull up subsequently. In this case the energization of one of the switching relays 50, 51 momentarily grounds the lower talking wire as in the first selector. Connector, Fig. 8. This is controlled in the ordinary way except that in the absence of a discriminating impulse the line relay 86 first energizes in series with a wiper-changing relay 118 which locks up and is then disconnected by the release relay 88 which cuts in the line relay lower winding in its place. Otherwise the relay 118 is short-circuited in the same way as relay 49 in the second selector. Inter-exchange working. Repeaters are provided with an additional relay, the control and function of which are similar to those of relay 49, Fig. 7. Certain features of the selectors are claimed in the divided Specifications 226,467 and 226,468.