Electro-Detection detects free e.m. radiation from buried metallic objects, and is typically used in the location of live or metallic services. The system responds either to radiation resulting from currents induced from external sources such as Long Wave radio transmissions, or mains electricity supplies, or from imposed currents introduced by a frequency generator coupled to the service in question. This latter provides a unique reference signal, and allows the route of a particular pipe or service to be tracked easily.
Currents can be imposed on a buried service either by making an electrical connection, or coupling inductively, in which the field is generated in the close vicinity of a known object and then tracked through the building.
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