Patent ID: 8548751

Claim:
A system for measuring a deflection from a normal position of an essentially longitudinal hollow component of a wind power installation, comprising: a) at least one distance sensor within the hollow component disposed in a first position for contact-free, directed distance measurement in the direction of a second position located within the hollow component and longitudinally spaced from the first position along a longitudinal axis of the hollow component so that the second position is longitudinally spaced in a longitudinal measurement direction from the first position; b) at least one measurement target disposed at the second position and scanned by the at least one distance sensor, with a target surface that extends in a measurement area transversely to a reference plane, which is perpendicular to the longitudinal measurement direction of the at least one distance sensor, viewed in either direction; and c) a computer unit for evaluating the distances determined by the at least one distance sensor to the target surface and defining a deflection of the hollow component from the normal position in any case with respect to the directional components of the directions, in which the target surface runs transverse to the reference plane, from these data.