Audi Q7 2017 Manual page 11

Measurement of longitudinal vehicle movement in X, Y and Z directions
The sensors for the measurement of longitudinal vehicle
movement in X, Y and Z directions work on the "seismic
mass" principle.
Design of the sensor
A moveable mounted mass (seismic mass) is integrated in
the sensor at a defined distance to a stationary capacitor
plate acting as an electrode. The seismic mass also has
electrodes, which combine with the stationary electrodes
to form a capacitor.
Rest position
X
Direction of measurement
Spring element
Capacitor plate
(movably mounted)
Capacitor plate
(stationary)
Seismic mass
Housing
637_014
An acceleration force acting on the sensor changes the
position of the seismic mass relative to the stationary
capacitor plate. This, in turn, changes the physical magni-
tude of the capacitance, which is processed digitally and
evaluated.
Movement
Z
637_013
637_015
7
Y