Patent ID: 8766639

Claim:
A proximity detection method for a conductive, buried structure, comprising the steps of: generating an alternating electrical current of a desired frequency by a current-source; introducing the electrical current into the structure so that an electromagnetic field is emitted, by the current-carrying structure; detecting the time-variable electromagnetic field by a mobile detection-unit above ground that is electrically insulated from the ground; determining the proximity of the structure to the detection-unit according to the detected electromagnetic field; indicating the proximity as a distance information between the structure and a reference point with a known position relative to the detection-unit, wherein at least first and second single point electrodes are stuck into soil so that the electrodes are surrounded by soil material, are spaced approximately 5-200 meters apart from each other, and are introducing the electrical current by conduction directly into the soil such that the flow-path of the electrical current is: from the current-source to the first electrode; from the first electrode through soil to the structure so that they are conducted by soil material only; following at least a part of the structure as path of least resistance underground; from the structure through soil to the second electrode so that they are conducted by soil material only; and from the at least second electrode to the current-source by an insulated cable above ground, wherein the first and the second electrode define a detection-area wherein the step of detecting the electromagnetic field is executed, and wherein the current-source is equipped with a system to detect whether the electrical current is flowing along the flow-path with a desired strength.