Figure 23 Tilt Error Magnitudes; Figure 24 Definition Of Pitch And Roll - Philips KMZ51 Application Note

Philips Semiconductors
Electronic Compass Design using
KMZ51 and KMZ52
shows tilt error versus tilt angle for two loactions on earth. Inclination values for locations world wide are
available at [1].
A classical method for avoiding tilt errors is to put a compass into a liquid, which provides horizontal levelling of
the compass due to gravity. This is often referred to as "mechanical gimbaling". However, as the compass here
is not fixed within its housing, interference fields caused by this housing are no deterministic signals anymore
and can therefore not be calibrated (refer to section 7).
Tilt error can be compensated without moving parts by converting the measured earth field components
mathematically into the horizontal components. This technique is often referred to as "electronical gimbaling"
and requires additional sensor elements:
•
A third magnetic field sensor, as now all three cartesian vector components of the earth´s field, i.e. Hex,
Hey, Hez have to be measured.
•
Sensors for pitch and roll to detect the tilt status of the compass. Pitch and roll are terms coming from
aviation. As shown in Figure 24, pitch refers to a tilt along the x or heading direction (= rotation around the y
axis), whereas roll refers to a tilt along the y axis (= rotation around the x-axis).
70,00
60,00
Hamburg,
inclination = 68°
50,00
40,00
30,00
20,00
10,00
0,00
0 10 20 30 40
tilt angle in degree
Figure 23 Tilt error magnitudes
pitch
φ
com-
com-
pass
pass
Xc
Yc
ρ
roll
Zc
Figure 24 Definition of pitch and roll
Singapore,
inclination = 13°
50 60 70 80 90
Xe (heading)
horizontal
plane
Ye (right)
gravity
32
Application Note
AN00022