Identification of metallic underground utilities with electrical continuity: Utilizing electromagnetic transmitters and receivers to locate conductive utilities like Phone, Gas, Cable/TV, Sewer, Water, Storm, Electrical Etc…
An active signal is a signal that has been artificially generated by an external source. Active radio detection methods can allow different services such as telephone 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 clip or 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, 65 or 83KHz frequencies are used. It is often possible to determine the depth of the service in these modes.
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.
Radiodetection: Fundamental Principles and Techniques
Pipe and Cable Locators don’t find pipes and cables, they find electro-magnetic fields. Why is that? Electro-magnetic fields do things and function in ways that pipes and cables don’t.
Underground conductors don’t move, but the electro-magnetic fields we detect and trace are subject to distortion affected by;
- Method of Signal Application
- Peak or Null
- Frequency Applied
There are three ways to locate a buried conductor;
- Put a field ON it.
- Put a field IN it.
- Look for a field that’s ALREADY on it.
It takes specialized equipment and training for successfully detection.