Method and sensor setup for determination of deflection and/or strain for failure detection

An elongated member of a wind turbine component subject to strain, the elongated member having a first, second and third points all along a same side of the elongated member and where the third point is arranged between the first and second point, comprising:

• a sensor unit arranged along the elongated member, where the sensor unit detects a deflection and/or strain of the elongated member between the first and second points, the sensor unit comprising
• a proximity sensor that determines a distance between the second point and the third point,
• an inflexible support that connects the first point to the third point, where the distance between the first point and the third point being longer than the distance between the second point and the third point, and
• a frequency detecting unit connected to the proximity sensor wherein the frequency detecting unit detects a frequency of a change of the distance between the second and third points.

A method for determining the deflection of an elongated member of a component of a wind turbine where the component has a plurality of sides, comprising:

• assigning a first point, a second point and a third point along a same side of the elongated member where the first, second and third points are all co-linear and where the third point is arranged between the first and second points and the distance between the first and third points is greater than the distance between the second and third points;
• connecting the first point to the third point by an inflexible support;
• determining a distance between the second point and the third point in time steps;
• and
• analyzing a frequency of a change of the determined distance to detect frequency changes.

A method for determining a strain of a plurality of elongated members, comprising:

• assigning a first point, a second point and a third point along a same side of the elongated member where the first, second and third points are all co-linear and where the third point is arranged between the first and second points and the distance between the first and third points is greater than the distance between the second and third points;
• connecting the first point to the third point by an inflexible support;
• determining a distance between the second point and the third point in time steps;
• and
• analyzing a frequency of a change of the determined distance to detect frequency changes.