| 摘要 |
The invention relates particularly to sensing devices and techniques which may be used to provide measurement data to aid an inertial navigation system, or attitude and heading reference system, and so bound the growth of errors which increase with time in such systems when operating autonomously. In one aspect, the invention relates to a method of determining the path length along a borehole from a known reference point to a probe or tool which progresses through a drillpipe or tubular string, to provide data to aid an inertial navigation system. A sensing device 15 is used to detect joints 11 between sections of drillpipe or tubular string within the borehole and the path length is determined from the number of joints detected and a known length of each section of drillpipe or tubular string. In another aspect, a flow measuring device, such as an impeller, is used to measure the velocity of the probe or tool through the drillpipe or tubular string. In another aspect the invention relates to a method of determining the velocity of a probe or a tool moving through a drillpipe or tubular string to provide data to aid an inertial navigation system. Two sensing devices, which are spaced apart by a known distance on the probe or tool, are used to detect one or more positions within a drillpipe or tubular string, and the velocity of the probe or tool is determined from the elapsed time between each sensor detection of the or each position and the distance between the sensors.
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