Detecting the condition of a concealed object

摘要

A system for detecting faults in the insulation layer surrounding a concealed conducting pipe (10) includes a signal generator (12) for applying an alternating current with a frequency of around 4Hz to the pipe, a magnetometer (102) for detecting the alternating current from the pipe (10) and a CPU (115) for identifying changes in the gradient of the detected current along the length of the concealed conducting pipe (10) which are caused by the faults in the insulation layer. The magnetometer (102) is used in connection with a locator(100) which detects a second alternatinq current applied to the pipe (10) by the singal generator (12), this second alternating current having a frequency of around 128Hz. The system can also use both these signals to determine the direction of the signals emulating from the pipe (10). <IMAGE>