Page 145 - Lehrbuch Neigungsmessung deutsch 2018.indd

COMPENDIUM INCLINATION MEASUREMENT
WYLER AG, WINTERTHUR / SWITZERLAND

The diagram in Fig. 2 shows the deviation of the measured angle from the effective one as a function of
the gravitational force and of the effective angle itself. With increasing angles, the deviation increases as
well. In Singapore, where the gravitational force is with 9.781 m/s one of the lowest, the deviation at 45°
2
is 0.1525°. Horizontally no deviation occurs.

Fig. 2 Deviation of the measured angle from the effective one as a
function of the gravitational force and of the effective angle

The angle is always measured against the local gravity vector. Anywhere on Earth away from the equator
or poles, effective gravity points not exactly toward the centre of the Earth, but rather perpendicular to the
surface of the geoid. This difference is called vertical deflection. Due to the flattened shape of the Earth, it
is directed somewhat toward the opposite pole. About half of the deflection is due to centrifugal force, and
half because the extra mass around the equator causes a change in the direction of the true gravitational
force relative to what it would be on a spherical Earth. Further influences are caused by mountains and
by geological irregularities of the subsurface and amount up to 10“ in flat areas or 20-50“ in alpine terrain.
At the place of measurement, the displayed angle can be corrected when the local gravity is taken into
account. Since it is not known in advance where the sensors will be used, it is not possible to calibrate
them to compensate for a different gravitational force. At the moment it is up to the customer to apply the
correction formulae to obtain the most accurate results. However, WYLER AG has developed a tool that
will allow adjustment of the calibration data to the local gravitational force.

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