Linear wheel speed sensor The linear wheel speed sensor is mainly composed of permanent magnet, pole shaft, induction coil and ring gear. When the ring gear rotates, the tooth tip and the tooth gap alternately face the polar axis. During the rotation of the ring gear, the magnetic flux inside the induction coil alternates to generate an induced electromotive force. This signal is input to the electronic control unit of the ABS through the cable at the end of the induction coil. When the rotation speed of the ring gear changes, the frequency of the induced electromotive force also changes.