PARSAN Geophysics

ISO 9001-2008 Certified Company

Induction Locator

Back to Techniques

Detection of Live Power Cables & Telecom cables

Radio-detection uses the principles of electromagnetic to detect underground utilities. This principle works on the basis that a current flowing along a conductor creates a magnetic field, which extends around the conductor in concentric circles. A receiver coil can be used to detect the amplitude of this magnetic field. The amplitude varies depending on the position and orientation of the receiver within the field. The amplitude is maximum when the receiver is in line with the field and directly above the conductor. Moving the receiver from side to side it is possible to follow the maximum signal response and, therefore, the line of the buried service.

Both active and passive methods are used to ensure all possible detectable services are located.

Active Methods

An active signal is a signal that has been artificially generated by an external source. Active radiodetection methods can allow different services such as BT and electric to be individually identified. Active methods involve the use of a transmitter. The transmitter can either be used for direct connection or for induction. Direct connection involves the application of an active signal to a conductor using a clamp. Induction involves a signal being radiated from the internal antenna of the transmitter, which is induced to any conductors in the vicinity and re-radiated. Generally 8, 33 or 65KHz frequencies are used. It is often possible to determine the depth of the service in this mode.

Passive Methods

A passive signal is a signal that occurs 'naturally' on a buried conductor. Passive radio detection methods will provide an indication only that services are present underground. Passive methods use the electro-magnetic fields already present around the underground utility to locate them.

Two modes are generally used:

  • Power -detects 50-60Hz energy present on most buried conductors
  • Radio -detects re-radiated radio energy often present on conductors -it is not possible to determine depth in this mode.

The radio-detection method, coupled with GPR, provides excellent data on underground utility network.