Purpose
The rod sensor and the pole wheel pick up the rotary motion of the wheel. The pole wheels for medium-duty and heavy-duty commercial vehicles have 100 teeth; for wheels with a smaller rolling circumference, pole wheels with 80 teeth may also be used. Because of the diagonal reference speed generated in the ECU, the ratio of the number of teeth and the wheel circumference on the front and rear wheels must be identical
to an accuracy of a few percent.
Operation
The bar sensor operates inductively and essentially consists of a permanent magnet with a round pole pin and a coil. The rotation of the pole wheel connected to the wheel hub produces a change in the magnetic flux picked up by the sensor coil, thereby generating an alternating voltage.
The frequency of this voltage is proportional to the wheel speed.