Patent GB-191422549-A (GB)
Title: Improvements in Intercommunication Telephone Systems.
Inventor: KERSTING CHARLES BERTRAM
IPC: H04M9/00
Filed: 1914-11-14
Granted: 1915-11-11
Abstract: 22,549. Kersting, C. B. Nov. 14. Intercommunication systems and apparatus.- Each station is provided with a selector switch which automatically selects and indicates the calling station when the hand-set at the called station is removed from its hook; while overhearing by an uncalled subscriber is prevented by short-circuiting the receiver when the hand. set is removed. In the arrangement shown, each station 1<1>, 2<1>, 3<1> is provided with an automatic selector switch 3 comprising a set of contacts connected to the lines, and a switch arm operated by a spring against the action of a retarding-mechanism consisting of a train of wheels 6 and a fly 20. The switch is moved to and retained in its normal position 16 when the hand-set H is replaced upon the hook 10. The motion of the switch 3 is arrested in its correct position by means of a two-coil magnet E, the armature 18 of which is adapted to engage a notched plate 5 when one of its coils 9 is energized. The plate 5 carries numerals, by means of which the calling station is indicated to the called subscriber. Each station is also provided with a hand selector switch 12, a ringing-key 11, and a bell 13. The operation of the arrangement is as follows. When station 1<1> desires to communicate with station 3<1>, the switch 12 at station 1<1> is connected to line L<3> as shown and the ringing-key 11 depressed, whereupon the bell 13 at station 3<1> is energized as follows: positive pole of battery R, key 11, line L<3>, home line of station 3', switch hook 10, bell 13, negative pole of battery R. The handset H is then removed from hook 10 of station 1', whereupon the automatic selector 3 moves to the position shown, completing a local circuit at station 1<1> as follows: battery B, arm of selector 3, contact 14, coil 8 of magnet E. The armature 18 is then attracted to engage a contact 17 on the plate 5, thereby short-circuiting the receiver 1, since plate 5 is in engagement with a contact 4. When the subscriber at station 3<1> removes the hand-set H from the hook 10, the automatic selector 3 is released and moves slowly over its contacts until it reaches the contact connected to the line L', whereupon the following circuit is completed: positive pole of battery B at station 3', arm of selector 3, line L', hook 10 and contact 19 of station 1<1>, coil 9 of magnet E, battery B of station 1<1>, arm of selector 3, contact 15, switch 12, line L<3>, switch hook 10 and contact 19 of station 3', coil 9 of magnet E, negative pole of battery B. The energization of the coil 9 at the called station 3' causes the armature 18 to engage the notched plate 5, thereby arresting the selector 3 in its correct position; while the energization of the coil 9 at station 1<1> neutralizes the effect of the coil 8, and the short-circuit about the'receiver 1 is removed at the contact 17 when the two stations are in communication. The arm of the selector 3 is connected to the retarding-mechanism by means of ratchet mechanism 7, in order that the arm may be returned rapidly to its normal position when the hand-set H is replaced. The subscriber at station 2' is prevented from overhearing the conversation between the subscribers at station 1<1>, 3<1> since, if the hand-set H at station 2<1> is removed from its hook, the arm of the selector moves until it engages contact 14, whereupon the receiver 1 is short-circuited by the action of the winding 8.