Modern wheel sensors are able to do more, indeed, they also have to be able to do more. One example: The hand-brake should automatically hold the vehicle on a hill, until the engine manages to turn the wheels forwards a little. It should only do this, when driving up- and not down a hill. You can see by this example, that a wheel sensor must not only register the slightest movement of the wheel, but also the respective rolling direction.
This can occur through a thin layer of magnetized iron. If a magnet is moved past this, a precise point of vertical effect is given. From this position, the smallest changes in one or the other direction cause the respective rotation of the magnetic field of the iron layer (anisotropic magnetic resistance). This can be measured and evaluated.
In the meantime, it is probably undisputed, that sensors which have their own power supply, as well as sending out useable signals to any number of other control devices, are described as being active. Passive wheel sensors, on the other hand, deliver an analog signal, which, e.g., can only be analysed above a speed of 7 km/h. The new generation of wheel sensors also has a higher immunity to corrosion and other possible errors.
With the delivery of the data a, e.g., too large or altered distance, through the rotation of the wheel, can also be transmitted. In the future, there will be more and more sensors which have their own fault detection. Indeed, a sensor which is integrated into the data-network, can at the same time, take over the transmission of other data, e.g., the rate of wear and tear of the brake pads and perhaps even soon, that of the tyre-pressure control as well. 02/13