The notched wheel is mounted directly behind the brake rotor or brake drum. The sensor detects the notches as the wheel rotates and develops a signal that is fed to the systems electronic control computer. The computer then calculates the vehicles acceleration, deceleration and skid factors. These factors are used to send control signals to a hydraulic valve which can control the amount of brake pressure at each wheel independently. When the system detects wheel lockup it can rapidly pulse the brake pressure up to 18 times per second.
ABS is a fine example of how sensors can be employed to control a vehicles stopping power.
Currently, there are systems being offered on 1999 model cars that can enhance a vehicles stability and control. The systems are centered around the vehicles ABS which is used to control the vehicles path. In order to do this, sensors are employed to monitor brake pressure, accelerator position, steering wheel position and speed, G-force, and axle sensors to monitor yaw rate. This anomaly most often occurs during sudden lane changes or when the operator over corrects. The vehicles stability control computer uses all of the sensor information to calculate the best yaw rate for the vehicles current speed.