POSITION DETECTION DEVICES

摘要

A position detection device for detecting the position of adjustable stabilizer blades (3) in a bottomhole assembly of a drill string (2) within a borehole comprises a variable reluctance magnetic circuit incorporating an inner magnet member (7) and an outer magnetisable member (4) which are movable relative to one another along a predetermined direction (5) between two states in which the reluctance of the magnetic circuit differs due to the differing relative positions of the inner and outer members (7, 4). The inner member (7) includes a detector (8) comprising a permanent magnet (9) having magnet poles oriented so as to provide a magnetic field having a portion extending transversely of the predetermined direction (5), and a magnetoresistive flux sensor (15) having a sensing axis (17) oriented relative to the magnet poles so as to provide an output indicative of the angle between the sensed flux in the vicinity of one of the magnet poles and the sensing axis (17) and dependent on the relative positions of the inner and outer members (7, 4). Such a novel position detection device provides a positive indication of the position of the stabiliser blades in such an application.