The wheel speed signals are made available by four "active" speed sensors.
These active speed sensors operate in accordance with the Hall principle, in which changes in the magnetic field strength produce alternating voltages with the frequency used as a measure for the wheel speed. In contrast to the passive speed sensors, the actual sensor element and electronics for signal conditioning are integrated in the active speed sensors.
Advantages of active sensors:
The speed signals are square-wave signals with constant amplitude (low level = 0.75 V, high level = 2.5 V), frequencies within the range from 0 ... approx. 1700 Hz are obtained for the speed range from 0 ... 250 km/h dependent on the tyre circumference.
The ABS/DSC control unit provides the voltage supply to the active sensors (7.6 ... 8.4 V direct voltage).
The wheel speeds are also required by other control units, for instance, the instrument cluster electronics (IKE) or electronic damper control (EDC). The speed signals are correspondingly processed in the ABS/DSC control unit for this purpose.
The speed output signals are square-wave signals with constant amplitude (low level < 1 V, high level > 11 V). The frequency is dependent on the wheel speeds and is within the range from 0 too 1700 Hz (0 to 250 km/h).