Patent GB-200845-A (GB)
Abstract: 200,845. Lenaghan, T. Jan. 16, 1922. Automatic exchange systems.-The system described in Specification 152,702, in which the movement of a selector is stopped by the deenergization of a differential relay when the selector finds a resistance &c. corresponding to a resistance recorded on a register-controller, is modified so that resistances of only two values are employed, as indicated by the short and long resistance symbols in Figs. 2 and 2<A>. This involves in some cases a hunting movement in the register-controller during which balancing conditions are established alternately through high and low resistances. A five-digit number is recorded on the registers RC<1> - - RC<5>, Fig. 2, and controls a group selector TS, Fig. 2<A>, and a final selector LSA or LSB, these selectors being of the kind described in Specification 189,822. The selector TS has five sets of wipers each giving access to 120 trunks divided into three groups of 40, and each group of 40 trunks is again divided into two sub-groups, one sub-group being characterized by battery balancing potential as at 22 and terminating in final selectors of the group LSA while the other sub-group is characterized by ground balancing potential and terminates in final selectors of the group LSB. The final selectors have five sets of wipers each serving 100 lines. It will be seen that the system has a capacity of 15,000 lines and that selection takes place on a non-decimal basis. It will be assumed that the registers are set for the number 23468, in which case the second set of wipers of the selector TS is moved to select an idle trunk of the third group and of the sub-group leading to the final selectors LSA; the fourth set of wipers of the selector LSA is then moved to its 68th set of terminals, first selecting a group of 20 lines and then the particular wanted line. The successive operations take place under control of a six-position switch 14, Fig. 2. Group selector TS. With the switch 14 in its first position the middle of the differential relay 10 is grounded through the register wiper 1<A>, its left-hand winding is connected to battery through resistance R<2> by the wiper 1<B>, and its right-hand winding is connected to a circuit 11, 6, 15, 16, so that when the wiper-choosing element of the selector TS reaches its second position the relay 10 is balanced and relapses and closes a circuit 33, 13, T, 7, 17. The trip magnet 17 stops the wiper-choosing movement, shifts the switch 15, and connects the magnet 118 to circuit 7. The magnet 13 moves the switch 14 to its second position. The middle of relay 10 is now connected through C to battery, its left winding through B, wiper 2<B>, and resistance R<IA> to ground, and its right winding through 11, 6, 15, 18, 19. When the auxiliary wiper 19 arrives on the low resistance R<IA> the relay 10 is balanced and closes a circuit 33, 34, S, 8, and the magnet 8 lifts the wipers 2<A>, 2<B> one step, substituting the resistance R<2c> for R<IA> so as to unbalance the relay 10. When the wiper 19 arrives on the high resistance, R<2c> the relay 10 is balanced again and the magnet 8 raises the wipers 2<A>, 2<B> a second step to substitute the resistance R<IB> for R<2C>, and when the wiper 19 arrives on the low resistance R<IB> the relay 10 is balanced and closes a circuit 33, 13, T, 2<A>, 7, 118. The trip magnet 118 shifts the switch 18 to connect the circuit 6 to the wipers 21 of the selector TS and transfers the circuit 7 to magnet 20. The magnet 13 moves the switch 14 to its third position. The second set of wipers, which alone has been tripped, are now at the commencement of the third group of 40 trunks. The test circuits of trunks leading the final selectors LSA serving lines whose hundreds digit is 1 - - 5 are connected to battery as at 22, while those of trunks leading the selectors LSB serving lines whose hundreds digit is 6 - - 0 are grounded as at 23. The determination as to which group of trunks shall be tested is made by the wipers 3<c>, 3<D> of the hundreds register, which pass current in one or other direction through the left winding of relay 10. When the relay 10 is balanced on the wiper 21 reaching an idle trunk of the appropriate series (in the present instance, a trunk of the series LSA) it energizes magnets 20 and 13 to stop the selector and to move the switch 14 to its fourth position. Final selector LSA. In the fourth position of the switch 14 the wipers 3<A>, 3<B> of the hundreds register control the selection of the fourth set of wipers of the selector LSA in a manner similar to that described for the selector TS, and the switch 14 is moved to its fifth position, in which the selected wipers are moved to the group of 20 lines in which the wanted line is comprised. This is effected by the wipers 4<A>, 4<D> of the tens register, which closes a circuit in one or other direction and including high, low, or no balancing resistance through the left winding of relay 10, so that this relay is balanced when the auxiliary wiper 29 of the selector finds corresponding conditions. Magnets 13, 27 are then energized and 'the switch 14 moves to its sixth position, in which the middle of relay 10 is connected to wiper 4<B>, 'its left winding through wipers 39 and 4<C>, and its right winding through 6, 21, 24, 28 to the fourth test wiper 31. The balancing circuits passed over by this wiper contain alternately low and high resistances, and those corresponding to odd tens digits are connected to battery while those corresponding to even tens digits are connected to ground. Since the tens register RC<4> has been set to an even position the middle of relay 10 is - connected to battery and this relay can only be balanced when the wiper 31 passes over grounded (even tens) lines. As soon as the wiper 31 reaches a grounded low-resistance line the relay 10 is balanced and energizes magnet 9 (over 33, 34, S) which raises the wipers 37, 38, 39 one step, substituting a high for a low resistance in the left winding of relay 10, so that this relay is unbalanced, but when wiper 31 reaches the next grounded high-resistance line, relay 10 becomes balanced again and again energizes magnet 9 to step up the wipers 37, 38, 39, restoring a lowresistance condition in the circuit of the left winding of relay 10, and in this way the wipers 37, 38, 39 are stepped up in synchronism with the movement of the selector over the wanted tens group until the wiper 37 reaches the level to which the units register RC<5> was set, when the balancing of relay 10 closes a circuit 33, 13, T, 37. RC<5>, 7, 30 to stop the selector. Private branch exchanges. Of a group of lines to a PBX only the first line is balanced, and if this line is busy the selector is not arrested but travels over the remaining lines. The wipers 37, 38, 39 have meanwhile been raised a step so as to connect the wiper 38 to the circuit 7, and a circuit 41, 35, 38, 7, 30 is closed to stop the selector as soon as relay 11 is de-energized as a result of an idle line being reached.