Patent GB-397912-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1932-03-02
Abstract: 397,912. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. March 2, 1932, No. 6363. Convention date, March 2, 1931. [Class 40 (iv).] A double-wiper single-motion switch makes 5 steps per impulse with the help of a pair of relays 16, 17, Fig. 1, 105, 106, Fig. 2, which are energized and released by alternate impulses, and an additional wiper 25, 124, cooperating with groups of terminals multipled in the case of a group selector, Fig. 1, to cause the switch to stop on the 1st trunk of the wanted group and in the case of a final selector, Fig. 2, on the terminals preceding the 1st in the wanted group. If the group selector finds all trunks busy, busy tone is connected up by the stepping magnet and a holding circuit is provided for holding the impulse relay weakly to make further dialling ineffective but not to prevent release. The final selector, with the help of the relay pair 105, 106 is stepped into the group only by the odd impulses, the even impulses energizing the wiper-changing relay 112. It is able to wait on a busy line and ring it when it becomes idle. Group selector, Figs. 1 and 3. Line relay 13 repeats the digit to the dialling relay 15 and to relays 16, 17 which are arranged to be energized at the beginning and end respectively of each odd impulse and to be released in the same order by each even impulse, 16 being released by the energization of a reverse winding. 15 connects the control wiper 25 over a selfinterrupting contact to the stepping magnet 20, and 16 when energized grounds the 51st terminal (on which wiper 25 rests when the switch is in its normal position) and also the even groups of 5 terminals, and when deenergized the odd groups of 5 terminals. The wipers thus take 1 step for the 1st impulse and 5 for each succeeding impulse. If the upper junction is busy, 19 pulls up and on the relapse of 15 the driving magnet is connected over its self-interrupting contact to the lower test wiper 27. If the lower trunk also is busy the switch takes a step. When an idle line is found, switching relay 18 pulls up, disconnecting or locking 19 as required, and releasing 13, 14. If all trunks are busy, the switch is driven on to the 1st terminals of the next group where the control wiper 25 provides a circuit for holding the stepping magnet energized, the switching relay 18 being prevented from operating whatever the condition of the trunks. The stepping magnet connects up busy tone from ATB, a circuit over the busy tone transformer holding the line relay. Final selector, Figs. 2 and 5. At the end of the 1st digit the switch stops in engagement with the terminals preceding the 1st speech terminals of the wanted group, and dialling relay 104 falls back unlocking 105, 106 if necessary and energizing 107 which locks up. Relays 104, 105, 106 respond to the units digit as before but since 107 is energized their effect in this case is to energize the stepping magnet at each odd impulse and the wiper changing relay 112 at each even impulse. When 104 falls after the final digit it allows 109 which is already partially operated to complete the test circuit over 111 and connect the busy tone wire to the talking circuit. If the line is idle or when it becomes idle, the busy tone is cut off by 111 and the line is rung in the usual way. 111 is so adjusted that it cannot pull up if another final selector is testing at the same time.