User manual

Table Of Contents
Sting
Direction
HX HY HZ φ θ
H
N 90° 0.3645 0.0008 -0.9312 -68.6° 82.8°
NE 45° 0.2383 0.2321 -0.9430 -70.6° 37.7°
E 0° -0.0246 0.2914 -0.9563 -73.0° -7.4°
SE -45° -0.2508 0.1515 -0.9561 -73.0° -53.7°
S -90° -0.3212 -0.1064 -0.9410 -70.2° -101.2°
SW -135° -0.1979 -0.3218 -0.9259 -67.8° -143.1°
W 180° 0.0511 -0.3652 -0.9295 -68.4° 174.7°
NW 135° 0.2817 -0.2563 -0.9246 -67.6° 130.4°
Figure 8-11: Plotting Horizontal Compass Measurements
ACM Compass Calibration Step 2 – Plot Raw Measurements
Plotting the raw measurements of HX and HY shows the need for calibrations. HX and
HY, the normalized components of the magnetic flux, are mathematical compass coordinates by
definition and are proportional to the sine and cosine of the heading angle of the sting. As such,
the points should lie on a circle centered at the origin.
In Figure 8-11, the eight measurements are shown by asterisks and the vector average of
the points is marked by a cross (the measurements are not centered on the origin and they lie on
an ellipse rather than a circle).
The errors are caused by slightly different biases, gains, and alignments in the two
horizontal components of the compass, each of which measures local magnetic flux relative to
itself. The alignment errors add a bias angle (an apparent rotation about the vertical axis), which
can be ignored until the second stage of the compass correction.
8-19