Patent GB-231419-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1924-09-10
Abstract: 231,419. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Madsen, F. T.). March 28, 1924, [Convention date]. Automatic exchange systems.-Relates to systems employing backwardly- and forwardly-hunting switches linked together in pairs. The backwardly- and forwardly-hunting switches are linked together over a distributing frame which provides a simple means of re-grouping the switches from time to time according to traffic requirements. The link circuits are assigned for use in turn by an allotting switch, with which are associated common test relays for controlling the hunting operation of both the backwardly- and forwardly-hunting switches. When all the outlets available to a forwardly-hunting switch are engaged the corresponding link circuit is marked busy in the bank of the allotting switch. In the system shown, a calling subscriber A is extended to an idle group selector S over a link circuit pre-selected by an allotting switch FA and comprising a finder F and a secondarv switch SS connected over a distributing frame 1DF. The subscribers' lines and the first selectors S are divided into groups, the finders F serving the same group of subscribers' lines being cross-connected at the frame 1DF to secondaryswitches SS having access to different groups of first selectors S. When the subscriber A removes his receiver, the line relay 6 connects battery to the test wire 4<1> through the cut-off relay 5, and energizes a starting relay 68 in the allotting switch FA over the common start wire 14. The relay 68 closes a circuit over wiper 81 for the stepping magnet 24 of the preselected finder F, and connects the lower winding of test relay 67 to the finder test wiper 22 over wiper 84. The finder F hunts in known manner for the calling line, and when this is found the test relay 67 energizes, locks up over its upper winding, and at armature 72 disconnects the stepping magnet 24. The start relay 68 also closes at armature 76 a series circuit for the lower winding of a second test relay 66 and the stepping magnet 35 of the linked secondary switch SS over wiper 86, and connects the test wiper 37 of this switch to a point between the relav 66 and magnet 35 over wiper 85. The switch SS operates in the usual manner, and when an idle trunk is reached, the test relay 66 locks up over its upper winding, earths the release wire of the selector S, and at armature 63 shunts the interrupter contacts of the allotting switch stepping magnet 70. In consequence of the energization of both test relays 66, 67 and responsive to whichever pulls up last, the switching relay 25 of the finder F energizes, locks to the release wire, energizes the cut-off relay 5, and closes a circuit for a relay 69, which connects the stepping magnet 70 in parallel with itself. The stepping magnet 70 energizes, but the allotting switch is not stepped on since its wipers are advanced on the back-stroke of the magnet 70 the interrupter contacts of which are shunted at armature 63. The relapse of the line relay 6 disconnects the start wire 14, and after an interval the relay 68 relapses and unlocks the relays 66, 67, the former of which removes the shunt from the interrupter contacts of the magnet 70. The allotting switch FA is now advanced until the test wiper 82 engages an unearthed bank contact, when the relay 69 de-energizes and opens the circuit of the magnet 70. The release relay 42 of the selector S closes a circuit for a relay 56. the armature of which is included in a chain circuit so that if all the selectors accessible to the secondary switch SS are engaged, a relay 58 is energized and earths an auxiliary test conductor, such as 89, of all the links having access to this group of selectors. A stepping circuit is thereby closed over armatures 80, 63 for the allotting switch magnet 70. If the conductor 89 becomes earthed while the associated finder F and secondary switch SS are hunting. the allotter is stepped on, and another link is allotted.