Accelerometer inclination measurement

Figure 4-225 shows the inclination measurement using a triaxial sensor featuring three accelerometers. The three coordinates of the earth s gravitational acceleration vector serve to define this vector in the reference frame of the probe. The earth s acceleration is computed as... 

Figure 4-225. Vector diagram of the inclination measurement with three accelerometers.

The accuracy of MWD directional measurements is generally much better than the single- or multishot-type measurements since the sensors are more advanced and the measurements more numerous. The azimuth measurement is made with the three components of the earth magnetic field vector and only with the horizontal component in the case of the single shot or multishot. The accelerometer measurements of the inclination are also more accurate whatever the value of the inclination. The average error in the horizontal position varies from... 

However, we know, that measurements with an accelerometer are distorted by other effects. For example these effects can be inclinations of the abutment as a consequence of the weight of the train or vibrations of the abutment during the brake tests. Accordingly the horizontal movements calculated by the equation (2) are not correct and we cannot use an accelerometer to determine the abutment motions without other information. 

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