A cable monitoring system with multiple branch terminations

摘要

A novel method and apparatus are used for monitoring cables for wear and damage. The system is particularly applicable to a cable system with multiple branch terminations. The cables have detection conductors, for example the metal cable jackets (24) or other detection conductors extending the length of the cables (14). These are connected electrically at the splice points (16) in the system. At the end of each branch (14) and at the end of the main cable (12), the detection conductors (24) are each connected to a novel termination circuit (22). In the normal monitoring mode, the termination circuit (22) appears as an open circuit. A DC voltage is normally applied to the detection conductors. Any current is a result of current leakage at a resistive fault along the detection conductors. The termination circuits are activated by altering the DC voltage, e.g. by reversing the polarity and increasing the magnitude of the voltage. This causes the termination circuit (22) to perform a series of functional tests. These include a loop test which places a short across the end of the detection conductor for a timed period. The resulting high level loop current is used to calculate the total detection conductor resistance. A second test transmits a coded signal simulating a triggered splice sensor unit. The signal is detected and decoded to verify proper operation of end to end coded signaling after completing a test cycle, the termination circuit turns off and the next termination to be tested is addressed. <IMAGE>