The need to sense speed and position of ferrous gears occurs in numerous applications. In order to detect the passing gear-teeth with a Hall Effect sensor it is necessary to provide a source of magnetic energy. The simple way to do this is to arrange a permanent magnet so that the axis of magnetization is pointing toward to surface of the gear-teeth. As a tooth moves across the surface of the magnet the flux will become attracted to the lower reluctance path provided by the ferrous steel structure. When this occurs the flux density measured by the Hall element between the face of the sensor and the gear-tooth increases. If the signal level changes beyond the preset magnitude from the positive or negative peak, the output level is changed. This creates a digital zero speed peak detection speed sensor. It is immune to orientation requirements and can follow the gear speed down to the cessation of motion.
It will detect the first edge of the next tooth immediately after power on.
Melexis has chosen to work with digital signal processing schemes and in this way minimize the magnetic circuit manipulation required by the end user.