Monitoring of alarm signal transmission cables for damage - uses capacitor coupled to sheathing that changes valve in event of damage

摘要

Detection of unwanted interference or damage to the transmission lines coupling an alarm detector to a receiver is provided by sensing a change in capacitance. Typically a sensor (A1) is coupled over two transmission cables (a1, b1) to a remote receiver (B1). The cables are located within a protective outer layer (S1). A capacitor (C1) is coupled between the shield and earth. Any damage to the shield produces a change in the capacitor rating and is used to trigger an alarm.