The Detector is used to locate submarine cables in water of up to 180 metres (100 fathoms) in depth. A signal in the range of 4 Hz to 40 Hz is transmitted down the submarine cable by an Electroding Generator such as the Tinsley type 5915 unit. This signal is picked up by a set of trailed probes connected to the detector. The Detector and receiving probes are normally aboard the repair ship, however, as they are portable, the detector may be operated from any locally available ship or launch. The received signal is processed and passed to the analogue front panel meter and if fitted, chart recorder.
Normally, the Electroding Generator, Tinsley type 5915, is located in the submarine cable terminal nearest to the fault area. The Electroding Detector, Tinsley type 5916 is aboard the ship. When the ship is in the vicinity of the cable area, the 5915 Electroding Generator is powered thus applying the low frequency signal to the cable under test. At these frequencies, the field of the signal extends into the water surrounding the cable for a considerable distance. The ship would normally steer a course to cross the cable on the landward side of the expected fault position. Before this position is reached, the ship launches the receiving probe(s) which will then connect to the detector.
The Detector is set (by thumbwheel switch) to the frequency being transmitted by the Electroding Generator on shore. As the ship crosses the cable, the field of the signal current on the cable induces a voltage into the probe(s). This signal is then processed by the Electroding Detector and a deflection on the meter is registered. This may be recorded by the optional built-in chart recorder.
For identification purposes, the Electroding Generator may be keyed on and off periodically.
Once the cable signal has been identified and confirmed, the ship then follows the cable on a zigzag course until the signal disappears. When this happens, the fault or break has been located. Use of NAVSAT on a marker buoy would mark the point where the signal was last detected. Further probe runs may be made for a more precise fix of the fault position.