Importance

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Abstract

An automatic audible signaling system for use in emergency warning and direction of people in the evacuation of buildings and the like comprises control apparatus at a central station, a plurality of local amplifiers mounted at remote locations, and at least one loudspeaker connected to each amplifier. The control apparatus comprises an audio preamplifier and, coupled to the output thereof, a modulation transformer having a center-tapped secondary to which a DC voltage is applied when it is desired to operate the loudspeakers. This arrangement supplies mixed DC power and low-level audio signal voltage to each of the remote amplifiers and obviates both the use of a high-power amplifier at the central station and the transmission of a high-power audio signal from the central control apparatus to the remote loudspeakers. The system also comprises supervisory means including a differential amplifier that normally produces no output but that, in response to a malfunction of the system, operates a relay that gives a trouble indication. The local amplifiers are specially designed to respond to the mixed AC/DC signal and to facilitate line supervision.

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First Claim