Improvements in alarm apparatus responsive to signals transmitted over electric lighting networks

Abstract

Abstract 507,300. Electric signalling systems; switches. POLIDORI, A. Nov. 26, 1938, No. 34513. [Class 40 (i)] [Also in Group XXXVII] In an alarm system more particularly for giving air-raid alarms, the alarm devices, e.g. electric bells, are operated by switches connected to the ordinary electric distribution network and operated in response to the re-establishment of the network current after an interruption of predetermined duration.- The responsive device for operating each alarm 17 comprises an electromagnet which is normally energized by the network current to hold a core 2, 3 in its upper position. The part 3 has teeth and notches 5, 6 which co-operate with a pawl 12 carried on a pivoted lever 9 which controls the alarm contacts 15, 16. The lever 9 is biassed to the position shown by a spring 10 and downward movement of the core 2, 3 is time-controlled by a dashpot 8. When it is desired to operate the alarm, the network current is interrupted and the core 2, 3 falls slowly until when the teeth 4 are opposite to the pawl, the current is re-established and the core is raised to operate the lever 9 through the intermediary of the teeth and pawl and close the alarm circuit. During the downward movement of the core, the pawl is deflected downwardly so that it is positioned to enter readily into one of the teeth when the current is re-established. A thermal switch 20 is included in the circuit of the electromagnet and is operated after a time-period by a heating resistance 19 in the alarm circuit to de-energize the electromagnet 1 and allow the core 2, 3 to fall and open the alarm circuit. Opening of the alarm circuit restores the switch 20 and the electromagnet is re-energized to raise the core into its normal upper position. Upon a normal interruption of the network current, the teeth 4 slide past the pawl without operating the alarm. In modifications, the rack 4 may be replaced by a toothed wheel or sector and an eddy-current brake may be used instead of the dashpot 8.

Inventors

No inventors recorded.

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