Baroid Technology, Inc.

Nl Sperry Sun, Inc.

Kenneth S Evans

Michael King Russell

Peter J Marlow

An accelerometer comprises a housing defining a chamber, a magnetizable fluid within the chamber, an electrically conductive, hollow cylindrical proof mass suspended within the chamber so as to be displaceble from a null position along a displacement axis by an applied force, and a sensing arrangement including electrodes on the inside wall of the chamber for detecting displacement of the proof mass along the displacement axis and for supplying an electrical signal indicative of the applied force. The proof mass is substantially non-magnetic, and magnets are disposed outside the chamber for magnetizing the magnetizable fluid to cause the proof mass to be suspended within the chamber by the fluid. Since there is no requirement for the proof mass to itself be magnetic as in prior accelerometers, it follows that there is no magnetic interaction between the magnetized particles of the fluid and the proof mass, and thus the effective mass of the proof mass will be substantially unchanged by changes in the distribution of the particles. Restoring coils are provided to restore the proof mass to a null position by inducing current flow in the proof mass.

Magnetic fluid rebalance accelerometers

An accelerometer has a housing defining a chamber, and a magnetizable fluid 11 within the chamber. A permanent magnet is magnetically suspended within the chamber by the magnetizable fluid with its poles oriented along a displacement axis so as to be displaceable from a null position along the displacement axis by an applied force. At least parts of the outer surface of the permanent magnet in the vicinity of its poles are provided with non-magnetizable end members. A sensing arrangement is provided for detecting displacement of the permanent magnet along the displacement axis and for supplying an electrical signal indicative of the applied force. Such an accelerometer is relatively immune to calibration drift and has high measurement accuracy.

Accelerometer having a permanent magnet with non-magnetic end members

A single-shot or multi-shot measurement probe incorporates a magnetic field sensor for sensing the earth's magnetic field, a processing unit for determining from the output of the sensor that the probe has moved from within a section of a drill pipe made predominantly of magnetizable material to within a collar made of substantially non-magnetizable material, and a switching unit for initiating the taking of one or more survey measurements by the probe when an output is received from the processing unit indicating that the probe has entered the collar. The probe further incorporates a gravity sensor for sensing the earth's gravitational field and a further processing unit for determining from the output of the gravity sensor that movement of the probe has stopped and for controlling the switching unit such that the taking of one or more survey measurements by the probe is not initiated until after receipt of an output from the further processing unit indicating that movement of the probe has stopped.

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Cheltenham, United Kingdom

Kenneth S Evans