| 摘要 |
<p>A combination of magnetics and a special geometric environment is employed to distinguish whether an instrument is positioned within a pipe formed of magnetizable or non-magnetizable material, and is the bases, in part, for a method and an apparatus used in controlling picture taking at the bottom of a well bore. A coil (20) is energized repetitively in a circuit (98, 118, 20) in which the voltage across the coil (20), or the current that flows through the coil (20), can be measured. Whether the coil (20) is in a magnetic (12) or non-magnetic (14) environment is determined by the magnitude of the change in coil voltage or current. </p> |
