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    • 6. 发明专利
    • DE4427367A1
    • 1995-02-09
    • DE4427367
    • 1994-08-02
    • HYDRIL CO
    • YOUNG KENNETH DCOLVIN KENNETH WFREDERICK JOSEPH L
    • E21B33/06E21B34/16G01B7/02E21B47/00
    • A ram of a ram-type blowout preventer is enclosed within an enclosure so that the piston 56 driving the ram is placed parallel to a stationary magnetizable waveguide tube 36. A transverse ring-like magnet assembly 64 surrounds the tube 36 and is attached to a carrier 54 that, in turn, is attached to the tail of the piston 56. The magnet assembly 64 longitudinally magnetizes an area of the tube where it is located. A wire running through the tube is periodically interrogated with an electrical current pulse, which produces a toroidal magnetic field about the wire. When the toroidal field intersects with the longitudinally magnetized area, a magnetostrictive acoustical return pulse is reflected back up the tube for detection by a transducer 32 located outside of the enclosure. The time that the acoustical pulse travels from the magnetic field intersection compared to the timing of the electrical pulse on the wire is a measure of distance since the pulse time essentially travels at the speed of light. Thus, the position of the ram is absolutely determined. From the position information from successive pulses, ram velocity and acceleration information can be developed. The measurements are continuous and absolute and are not incremental.