By the invention one or more bolt gauges (6) each with a built-in load cell (LC, not shown) are positioned on a blade bolt or a bearing bolt between a pitch bearing and a nut and tensioned by the nut at the inside or the outside of a hub of a wind turbine. The bolt gauge then outputs a signal descending both from the tension from the bolt/nut connection and the tension from the blade when the blade is vibrated due to wind forces and the rotation of the blade when the hub of the wind turbine is rotating. Further a severe and alarming change in each blade frequency is monitored as each blade frequency is compared to the other blade frequencies and an alarm is set and/or the wind turbine is stopped if a given level is reached.
