Patent GB-216591-A (GB)
Abstract: 216,591. Automatic Telephone Manufacturing Co., Ltd., and Bowland, R. March 2, 1923. Addition to 168,597. Automatic exchange systems.-An automatic switch normally operates as a group selector to find an idle group selector of the next switching stage, but if the first digit is of a particular value it is absorbed and the switch may respond to a further digit of any value and hunt to find a switch of the next but one switching stage. This is effected by a switch similar to that described in Specification 104,640, having two sets of wipers and associated bank contacts, the switch being released and the second set of wipers brought into use by the closure of a set of shaft contact springs, on the wipers being raised to a predetermined level. The invention is described as applied to a network of less than ten 10,000- line exchanges using first, second, and third group selectors for distant exchange calls. The switches in question are used to engage a second group selector when making a call to a distant exchange, but when raised to a particular level by a first digit which indicates that the call is a local one, the switch is released, connects up the second wiper set, and in response to the second digit operates to select an idle local third selector. Call to a subscriber at a distant exchange. When a calling subscriber's individual line switch engages an idle digit absorbing selector, the line relay 4 and release relay 5 are energized and a circuit is prepared for a series relay 7 and the vertical magnet 18. Dialling tone is sent back over the springs 12, and when the first digit is dialled the wipers are stepped up to the required level. Upon the closure of the off-normal springs 20, the stepping relay 8 locks energized over the shaft springs 25, and on the relapse of the series relay 7, a circuit is closed for the rotary magnet 23. The stepping relay 8 and the rotary magnet 23 now operate together in known manner until the upper test wiper 27 engages an idle trunk to the wanted exchange, when a shunt is removed from the switching relay 9, which extends the calling line 1, 2 to the upper line wipers 36, 37. If all the lines in the selected level are busy, the switch is driven to its 11th rotary position in which the springs 12, 35 are operated to disconnect the dialling tone and connect up the busy tone generator. Local call. This proceeds as above, but when the wipers have been raised to the critical level, the locking circuit of the stepping relay 8 is opened at the shaft springs 25, and the changeover relay 6 and the release magnet 38 are energized over the shaft springs 24. The switch is thereby restored, and the change-over relay 6, which locks up over its armature 30, connects up the second wiper set 40, 41, 42. The relay 6 also de-energizes the release magnet 38 at its armature 31, and at armature 32 places a shunt across the shaft springs 25, in order that even if the switch is raised to the critical level by the second digit, the release magnet is not operated and the locking circuit of the stepping relay 8 is not opened. The second digit operates the switch in the same manner as the first with the exception that the test wiper 40 controls the rotary movement.