| 摘要 |
A voice evacuation system using pulse width modulation of square waves at a frequency substantially higher than the voice signals. A number of amplifiers are connected in parallel to the distribution circuit. The signal from each amplifier is examined for the presence of the square waves. If no square waves are present, the amplifier is automatically disconnected from the distribution circuit. The remaining amplifiers are of sufficient capacity to carry the required load. The high frequency components are flitered from the signal before it is applied to the distribution circuit, leaving only the audio signals. Because of the nature of the coupling to the distribution circuit, a monitoring voltage and signals to operate auxiliary devices may be applied to the distribution circuit for supervision and operation of the auxiliary devices during actual operating conditions. The monitoring d-c voltage is applied through a resistor to the distribution circuit, which is terminated by a resistor, and the voltage on the distribution circuit is monitored to determine the condition of operation of the circuit. Operation of the auxiliary devices is unaffected by the presence of the monitoring voltage because of the polarity of that voltage and rectifiers in the auxiliary device circuits.
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