This is RUIAN FENGJIE AUTOMOTIVE PARTS MANUFACTURING CO. Ltd is a Chinese company focusing on producing ABS Wheel Speed Sensor
We focuses on development, production, sale of auto sensors.

We are very glad to send E-mail to you...We wish to inform you that we speciclize in BMW ABS WHEEL SPEED SENSOR, With self-contained developing and testing equipments of sensors, the ompany is now on leading position in the filed of new product development and production in China. And shall be pleased to enter into trade relations with you.
How it works:
There are two basic types of wheel speed sensor, passive and active;

1. Passive sensors;
These are similar in operation to Inductive cam/crank sensors; They consist of a soft iron, permanent magnetic pin around which is wound a fine copper wire coil. The unit fits in close proximity to a rotating trigger wheel. The trigger wheel is mounted onto a rotating assembly, such as the disc, drum or hub. When the trigger-wheel rotates past the pick-up assembly the alternating teeth generate a small inductive voltage in the copper windings. This voltage signal is used by the ECU as wheel speed information. Passive sensors generally only have two wires, one signal and one earth/shield.

2. Active sensors;
The operation of the active sensor can be likened to the Hall type sensor found in distributors etc. The pick-up assembly has an inbuilt amplifier and thus relies on a supply voltage which is normally 5v but it can be 12v.

The rotating element consists of a multi-pole (north, south, north, south ^) magnetic ring, which can be located onto a rotating assembly as with the passive sensor. There is an increasing trend to incorporate it into the wheel bearing seal and to use magnetic powder instead of fixed magnets.