ABS sensor, also known as wheel speed sensor, is a key component used in ABS (Anti-lock Braking System) of motor vehicles. In ABS system, wheel speed sensor is used to monitor vehicle speed. ABS sensor outputs a set of quasi-sinusoidal AC signals through the action of gear ring that rotates synchronously with the wheel. Its frequency and amplitude are related to wheel speed (magnetoelectric type), or the output signal is a square wave signal whose frequency changes with speed (digital type). The output signal is transmitted to ABS electronic control unit (ECU) to realize real-time monitoring of wheel speed. ECU calculates and decides whether to perform anti-lock braking.