BMW onboard monitor and navigation systems - E38.org

MAGNETIC FIELD SENSOR
In addition to the vehicle’s current position, the navigation computer also needs a direction
of travel input. The magnetic field sensor is used for this purpose.
The sensor consists of a ferromagnetic ring with two coils of wire placed 90 O apart. Signals
from the two coils become the vehicle’s directional input when the navigation system is in
operation.
SENSOR OPERATION
The sensor receives its operating power and ground from the navigation computer. When
the system is switched on, magnetic fields are induced into the coils. The coils produce a
voltage signal that is input to the navigation computer.
As the vehicle turns to the left or right, the earth’s magnetic field influences the coil’s
magnetic fields causing them to increase and decrease.
The changing strength of the magnetic fields causes the voltage signal induced in the coils
to increase and decrease linearly. This creates a changing voltage drop at the monitor in the
navigation computer.
The navigation computer determines the direction of travel of the vehicle by plotting the
simultaneously changing voltage signals.
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On-Board Monitor and Navigation Systems