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LINE SECURITY SYSTEM

  • US 3,641,547 A
  • Filed: 05/25/1970
  • Issued: 02/08/1972
  • Est. Priority Date: 05/25/1970
  • Status: Expired due to Term
First Claim
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1. A system for insuring the security of electrical transmission lines extending between a monitor station and a remote station, the system comprising a current regulator at the remote station, the current regulator being connected to the transmission lines and providing a quiescent pulsed direct current of constant level in response to an impressed periodic AC voltage, the current regulator having actuable means for causing the pulsed direct current to increase to a higher alarm current level upon the occurrence of an event at the remote station, monitoring apparatus at the monitor station, the monitor apparatus being connected to the transmission lines and comprising means for applying a periodic AC voltage to the transmission lines, an open line detector having its input signal obtained from the current flowing in the transmission lines, the open line detector providing an output signal in response to a drop in current below the quiescent current level, means for intermittently reducing the AC voltage applied to the transmission lines to a level barely sufficient to maintain the current at the quiescent current level when the impedance of the transmission lines is within the impedance range that is normal for such lines, a shorted line detector having its input obtained from the current flowing in the transmission lines, the shorted line detector providing an output signal in response to a reversal in the direction of normal current flow in the transmission lines, and an alarm current detector having its input obtained from the current flowing in the transmission lines, the alarm current detector providing an output signal in response to a rise in current to the alarm current level.

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