Front Wheel Speed Sensor

The CAB sends 12 volts to power an Integrated Circuit (IC) in sensor. The IC supplies a constant 7 mA power supply to CAB. The relationship of tooth on tone wheel to permanent magnet in sensor, signals IC to enable a second 7 mA power supply. The output of sensor, sent to CAB, is a DC voltage signal with changing voltage and current levels. The ground for IC and current sense circuit is provided by CAB.

When a valley of tone wheel is aligned with sensor, voltage signal is approximately 0.8 volts and a constant 7 mA current is sent to CAB. As tone wheel rotates, tooth shifts magnetic field and IC enables a second 7 mA current source. The CAB senses a voltage signal of approximately 1.6 volts and 14 mA. The CAB measures amperage of digital signal for each wheel. The resulting signal is interpreted by ABS CAB as wheel speed.