| 摘要 |
A downhole tool 130 for measuring accelerations at a location within a borehole 11 with an accelerometer 2 (fig 2), the tool being rotatable and comprising a plurality of accelerometers 2 configured to measure acceleration in a respective direction and arranged so at least a component of the measured acceleration is normal to the longitudinal direction, a first device 3/34 (fig 2) which measures rotational speed of the tool and a processor unit 370 which relates the acceleration measured by each accelerometer to the true acceleration to the true acceleration at that accelerometer by a respective scaling term and a respective offset and combines the measured accelerations and the tool rotational speed to re-calibrate the scaling terms as the tool rotates. The tool may further include a gyroscope 3 (fig 2) to measure the tool rotational speed, and my include magnetometer 4 (fig 2) to measure the earths magnetic field. The tool may further comprise a processor unit which filters the measured accelerations to the same bandwidth and which may have a bandwidth at most at 5% of the Nyquist frequency for accelerometer measurements. |
