| 摘要 |
<p>A snubbing unit (10), used to raise or lower a collar-connected series of tubing joints through a riser spool (14) communicating with a well bore, is provided with an electromagnetic sensing system (50) operative to detect and indicate the entry into, position within and travel direction within a sensing spool between the upper and lower blowout preventers (26, 28) of each tubing collar (24). The sensing system includes upper and lower electromagnetic coils (52, 54) coaxially circumscribing the sensing spool, and a frequency generator (58) for energizing the coils. First and second phase comparators (60, 62) are used to detect current phase alterations in the coils, caused by variations in the vertical proximity between each collar (24) and the coils (52, 54), and responsively transmit output signals indicative of such phase alterations. The output signals are sent to a position sensing circuit which utilizes them to illuminate collar position and travel direction lights on an operator control panel.</p> |
