A method of detecting the rotational speed of a rotary member, which comprises the steps of detecting, in sequence, a time period indicative of the interval between successive preceding and following angular positions of the rotary member, memorizing in turn from each of the angular positions of the...http://www.google.co.uk/patents/US4569027?utm_source=gb-gplus-sharePatent US4569027 - Method and apparatus for detecting rotational speed of rotary member
