| 摘要 |
The invention provides an electronic warning system, including an electrical line of a fence extending along a protected area; a pulser; a transmitter for transmitting pulses through the line; a receiver for receiving the pulses after being transmitted along at least a portion of the line; an impedance having a resistance substantially identical to the line characteristic resistance and connected at the end of the line, for absorbing the pulses when the pulses are received thereby at the end of the line so that the pulses do not return to the receiver; a plurality of sensors disposed at spaced-apart locations along the line and actuated responsive to phenomenon occurring in the vicinity thereof, for, when actuated, causing the pulses to return to the receiver; and a processor for operating the transmitter and receiver and for actuating a warning signal upon the detection, by at least one of the sensors, of the phenomenon. The processor has means for determining the time taken by a the pulse to return to the receiver in response to the actuation of the sensor so as to determine the location of the actuated sensor and thus determining the location at which the phenomenon occurred; characterized in that the processor further includes means for presetting and determining the number of pulses received during a preset period of time from receipt of a first pulse, resulting from an occurrence and repeated occurrences of the phenomenon at the same location, and for actuating a warning signal beyond the number of pulses. A method for distinguishing between false alarms and true unauthorized activity along a fence or at the vicinity thereof, is also provided.
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