Patent GB-191320856-A (GB)
Title: Improvements in Telephone Exchange Systems.
IPC: H01H67/06
Filed: 1913-09-16
Abstract: 20,856. Zivnostenska Banka v Praze. Oct. 28, 1912, [Convention date]. Automatic exchange systems and apparatus; selectors.-In systems in which each selector consists of a b-switch comprising a number of sets of rotatable brushes and an a-switch for selecting a. particular set of brushes of the bswitch, the a-switch of a group selector is restored to its normal position when a connexion is released, but the b-switch .is left in the position which it occupied during the connexion. A ratchet-driven selector of this type, and circuit arrangements comprising several special features, are described. Construction of selector. The brushes 60, Fig. 2, of the b-switch are mounted on a shaft 62 operated by a ratchet-wheel 71<1>, while the brushes 15, 16, 17, .18 of the a-switch are mounted on a sleeve 63 operated by a ratchetwheel 71. The bank terminals are arranged in a semi-cylinder as shown in Fig. 3, and the brushes are connected by springs 100 bearing on flanges 59. The arrangement of the brushes and terminals in pairs, on opposite sides of insulating-separators 64, 68, prevents lateral pressure on the. shaft 62. One form of ratchet driving-mechanism is shown in Fig. 7. The rocking armature 72 operates the driving-pawl 74, and, at the end of its stroke, brings a detent 83 against a reverse ratchet-wheel 84 to prevent over-drive. The detent 83 and reverse ratchetwheel 84 may be omitted, over-drive being prevented by a spring pawl bearing on the ratchetwheel 71. The driving-magnet may have two windings which are normally in series, but are automatically switched in parallel, to give a stronger drive, at the moment when the brushes are about to be driven on to the first terminals of the contact field. The sleeve 63 of the switch a carries a grooved disk 80 which operates a group of normal and off-normal contacts 9, 10, 11, 12, 13, Fig. 1. Circuit arrangements. Fig. 1 shows the circuits of a group selector which is operated by a series of impulses in the lead A followed by an impulse in the lead B. It is assumed that the selector shown is preceded and followed by selectors which are similarly organized. When the selector is seized, a relay VR in the incoming test-circuit is energized, and connects the magnet D<a> to the lead A. The magnet D<a> responds to the next series of impulses in the lead A, and operates the switch a to select the set of brushes of the switch b which serve the group of lines in which a connexion is desired. The succeeding impulse in the lead B energizes a relay ER, which locks a circuit through its own second winding and connects the battery to the test relay TR and magnet Db. As described in the next paragraph, the other terminal of the magnet D<b> is connected through the brush 18 of the switch a to an interrupter circuit, and the magnet Db is therefore intermittently energized and rotates the switch b. When the selected brushes of the switch b come to an idle line, the test relay TR is energized and disconnects the magnet D<b>, at the same time switching forward the line A, B and short-circuiting its own lower winding to mark the appropriated line non- selectable to other switches. The first impulse of the next series in the lead A not only energizes the setting-magnet of the next selector, but also (1) energizes a relay BR, which locks itself to the incoming test-circuit S by opening the contact 2 which normally short-circuits its third winding, and (2) unlocks the relay ER by energizing its third winding, which neutralizes the locking-circuit through the second winding. Preventing useless hunting of the selector when there is no disengaged line in the required group. The rotary magnet D<b> of the switch b is connected by the brush 18 to a wire which is common to all the lines of the group selected by the switch a. As long as any of these lines is disengaged, the group wire is connected to an interrupter through a back contact of the relay VR of each disengaged line, but if all the lines are engaged, the interrupter circuit is disconnected from the contact on which the arm 18 is set, and the magnet Db cannot be actuated. Signalling the calling subscriber when impulses are sent prematurely. If the selector should fail to find an idle line by the time the next set of impulses begins to arrive, the first of these impulses energizes the relay BR, as previously described, but does not unlock the relay ER, the contact 51 being open. The relay BR disconnects the magnets D<a>, D<b> to prevent further movement of the selector, and connects a buzzar circuit through its own fourth winding and that of the relay ER so as to send back an inductive signal to the calling subscriber. Preventing simultaneous seizure of the same line by two selectors. The energization of the test relay TR, when a selector seizes an idle line, connects the grounded resistance PW to the relay BR of the seized line. This relay does not, however, receive sufficient current to become energized unless two selectors are simultaneously attempting to seize the same line, in which case, the test-circuit of the seized line is opened at the contact 2 and the relays TR of the interferring selectors are de-energized, bringing the magnets D<b> again into action to search for another disengaged line. Release. When the calling subscriber disconnects himself, the incoming test-circuit S is interrupted and the relay VR de-energizes. This closes a restoring-circuit for the magnet D<a>, which moves forward the switch a until the normal position is regained, whereupon its circuit is opened at the off-normal contact 11. If the called subscriber should be the first to disconnect himself, the out-going test-circuit S is interrupted owing to changes at the final selector, and the de-energization of the relay TR opens the incoming test-circuit at the contact 53. The incoming test-circuit is closed again a moment later at the contact 2 by the de-energization of the relay BR, but in the interval the test relay TR of the preceding selector has been unlocked and has permanently opened the test-circuit, so that the relay VR is de-energized and the switch a restored to normal.