JPS5469100A - Disconnection detecting circuit for sensor circuit - Google Patents

Abstract

PURPOSE: To secure the instantaneous and automatic detection for the disconnection of the sensor circuit by using a wire of the sensor circuit flowing the monitor current at all times as the primary side of the current transformer and then detecting the change of the secondary output of the current transformer to deliver the disconnection detection signal.

CONSTITUTION: Sensor circuit L consists of line l₁ and common line l₂. And the starting end of line l₁ is connected to one end of full wave rectifying power source EV via territory relay RY provided to the receiver, and the starting end of l₂ is connected to the other end of EV in the receiver. Both lines l₁ and l₂ are led out from the receiver to be wired to each place. Then terminating resistance RE is connected to the termination of the line, and at the same time the sensors such as differential spot 1₁, smoke senson 1₁, constant-temperature spot 1₃ and others are connected to the intermediate part. Thus, the micro monitor current of about 3mA is flown at all times to sensor circuit L via relay RY and resistance RE. Current transformer CT uses the circular core and makes line l₁ of circuit L pierce through the through- hole to use it as the primary winding. Then disconnection detector circuit A detects the secondary output of CT to secure an automatic detection of the disconnection through the variation of the secondary output.

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