STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

910 Drilling and Well Completions
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
G=,/G;+G;+G; (4-173)
It must be equal to the 32.2 ft/s2; otherwise the accelerometers are not working
correctly. When the readings are in g units, G must be equal to one.
For the best accuracy, inclination less than 60" is computed with
dG; + G:
i = arc sin
G
(4-174)
and for i greater than 60"
G
i = arc cos2
G
(4-175)
PLANE NORMAL
TO COLLAR
TOR
Figure 4-225. Vector diagram of the inclination measurement with three
accelerometers.