Patent ID: 6965230

Claim:
An apparatus for positioning a power tong unit at a desired position along the longitude of an electrically conductive tubular, comprising: a) an electric coil operatively connected to a source of alternating electric current, thereby creating an electro-magnetic field therearound, said electric coil adapted to be placed radially with respect to and sufficiently close to an electrically conductive tubular so that said electro-magnetic field is influenced by the presence of said tubular; b) a means for moving said electric coil in a direction parallel to the longitude of said tubular, while said electric coil remains at a substantially constant distance from an outer surface of said tubular; c) a means for detecting a change in said electro-magnetic field of said electric coil in response to movement of said electric coil in a direction parallel to the longitude of said tubular, said means for detecting comprising a digital processor, and wherein said change in said electro-magnetic field comprises a change in at least one of impedance, current, and phase angle of said alternating electric current and wherein said change results from a connection end of said tubular within said electro-magnetic field, said change comprising data from which a height of said connection end above a datum may be determined; d) a power tong unit, comprising a power tong and a backup unit; e) a means for positioning said power tong unit at a desired position along a line parallel to the longitude of said tubular, said means for positioning operatively coupled to said means for detecting a change in said electro-magnetic field of said electric coil, and thereby positioning said power tong unit at said height above said datum corresponding to said connection end in response to a said change in said electro-magnetic field of said electric coil.