| 摘要 |
<p>PURPOSE:To make it possible to specify the position of an underground buried pipe in a state of noncontact by making a signal current flow directly through the underground buried pipe itself and by measuring a magnetic field generated thereby. CONSTITUTION:First, a high-voltage current is once impressed as shown by points A to D by a power source 12. At the outset of the impression, a very large resistance value is brought forth by a high withstand voltage in a joining part and the like and the current hardly flows. When this state continues for some time, however, the resistance value lowers rapidly and the current turns flowing sufficiently. In a stage wherein the resistance value, at least, lowers, a signal current being a high-frequency current is superposed and a magnetic field generated concentrically around a metal pipe 2 and metal pipes 3 and 4 (within a plane perpendicular to a horizontal plane) is measured. Thereby, a depth (h) can be determined. The position of the metal pipe 2 to be determined can be specified from this depth.</p> |
