Patent GB-409015-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1932-10-22
Abstract: 409,015. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. Oct. 22, 1932, No. 29605. Convention date, Nov. 9, 1931. [Class 40 (iv).] A rotary selector having access to groups of varying size and capable of taking a number of quick steps during the time of one impulse is stepped over the smaller groups in response to single impulses, but requires more than one impulse to effect its stepping over the larger groups. The digits designating the various groups are therefore arranged so that a group following one which is greater than could be passed over during a single impulse is designated by a digit greater by one or more than the digit for the preceding group. The switch described has two sets of wipers and a control wiper 25. The groups are not limited to ten contacts (five for each wiper-set) or multiples thereof, and one arrangement of the control bank is shown in Fig. 3 dealing with 8 groups of 10, 4, 18, 6, 10, 14, 10, 28 outlets. It will be assumed that the number of possible steps per impulse is 5 (10 outlets) so that to reach the commencement of groups 4 and 7 two impulses are required for passage over the preceding group and the digits are therefore 1, 2, 3, 5, 6, 7, 9, 0. The contacts in the control bank are commoned, within the groups, in sub-groups not exceeding five, the last contact in each group being connected to a wire 48 which is grounded during the setting movement. The sub-groups are connected alternately to wires 29, 30 which are alternately grounded by incoming impulses to provide self-stepping circuits for the switch magnet. In an inter-office system using code translating register - controllers where the maximum number of impulses need not be limited to ten, the selector is particularly useful as one having access to a large number of varying groups of outgoing junctions, and one arrangement of the control bank provides for 13 groups, the maximum digit being 16. Operation of selector. The grounding of the control wires 29, 30 by odd and even impulses may be effected by an auxiliary marking switch, but, as shown, relay 16 pulls up at the commencement of an odd impulse to ground wire 29 and releases at the commencement of the even impulse to ground 30, its circuits being controlled by relay 17 which pulls up at the end of odd impulses and relapses at the end of the even ones. The preceding switch hunts for battery on 11 and line and release relays 13, 14 pull up. Dialling relay 15 and relay 16 pull up at the first relapse of 13, and magnet 20 steps the switch from the normal last contact 51 (grounded over 29) to contact 1 which is not grounded by wire 30 unless another impulse comes in since relay 15 would relapse. On the next relapse of 13, ground is transferred from 29 to 30 by the release of 16, magnet 20 steps over the commoned contacts of the first group and over the grounded last contact to the first of the next group which is not grounded until the third relapse of 13. The switch is driven in similar manner to the commencement of the wanted group whereupon dialling relay 15 relapses to complete a hunting circuit for magnet 20 under the control of two test relays 18, 19 of which 18 is connected to the testwiper 23 of the first set and is purely switching relay, whereas 19 is connected to test-wiper 27 of the other set and is a wiper changing relay. The relapse of 15 also disconnects ground from wires 29, 30 to prevent interference with the hunting. If both outlets are idle, 18, 19 pull up simultaneously so that the lower set has preference ; if only the upper outlet is idle, 18 pulls up alone ; if only the lower outlet is idle, 19 pulls up first and connects 18 to operate it over the second test wiper 27. Busy signal. Busy tone from 46 is connected up immediately the dialling relay falls back, but is quickly removed by relapse of the release relay if an idle outlet is found. If, however, all outlets in the group are busy, the back stroke magnet 20 is maintained operated by ground on 48 over the last contact in a circuit independent of the magnet interrupter (15 has relapsed) and busy tone is maintained until the calling party releases. Magnet 20 opens the circuits of test relays 18, 19 to prevent their operation if an outlet becomes idle in the meantime.