Patent ID: 7117605

Claim:
A survey tool for determining an orientation of the survey tool within a borehole, the survey tool comprising: a plurality of rotation sensors, each rotation sensor having a sensing axis and a direction of least acceleration sensitivity, each rotation sensor adapted to generate a first signal indicative of a detected angular rotation rate about its sensing axis, the plurality of rotation sensors mounted in a housing with their sensing axes generally parallel to one another and with their directions of least acceleration sensitivity generally non-parallel to one another; a plurality of acceleration sensors mounted in the housing, each acceleration sensor having a sensing direction, each acceleration sensor adapted to generate a second signal indicative of detected acceleration along its sensing direction; and a controller adapted to receive a first signal from each of the plurality of rotation sensors and a second signal from each of the plurality of acceleration sensors, the controller adapted to calculate a weighted average of the detected angular rotation rates from the plurality of rotation sensors, the weighted average including the detected angular rotation rate of each rotation sensor about its sensing axis weighted by the detected acceleration along its direction of least acceleration sensitivity.