A rotational speed detection unit has a rotating tone wheel, a pole piece and a stationary sensor comprising a magnetic wire of the Wiegand wire or amorphous magnetostriction wire and a coil such that the tone wheel has an outer periphery with the alternative N and S poles with a uniform pitch, that...http://www.google.com.au/patents/US5663641?utm_source=gb-gplus-sharePatent US5663641 - Rotational speed detection unit
