Next to the brake piston (the caliper of the brake disc, inside the brake piston), the ABS work is to ensure that the brake piston and the brake disc are not stuck, to ensure that they are at the edge of sliding friction and static friction. Most of the vehicles are monitored by inductive sensors, and the ABS wheel speed sensor outputs a group of quasi-sinusoidal AC electrical signals through the action of the gear ring that rotates synchronously with the wheel, whose frequency and amplitude are related to the wheel speed. The output signal is transmitted to the ABS electronic control unit (ECU) to realize the real-time monitoring of wheel speed.