Abstract: An automatic transportation system comprises a track mounted on a floor, a carriage having a reaction plate movable along the track, and a plurality of stators mounted on the floor along the track. A linear induction motor (LIM) for propelling the carriage is formed by the reaction plate and one of the stators. The system further comprises a detector unit including a plate mounted on the carriage and having a pair of parallel spaced first and second rows of slots, and at least one detector device disposed adjacent to one of the stators located at stations. The detector device comprises a pair of spaced first and second sensors for respectively detecting the first and second rows of slots to output a pair of pulse signals 90.degree. out of phase from each other when the carriage passes thereby. An F/V converter converts the pulse signals into a signal representative of the direction and speed of movement of the carriage.