ISO 10816-21:2015 specifies the measurement and evaluation of mechanical vibration of wind turbines and their components by taking measurements on non-rotating parts. It applies to horizontal axis wind turbines with mechanical gearbox and rated generator output exceeding 200 kW and the following design and operational characteristics:

a) installation on supporting systems (tower and foundation) made of steel and/or concrete;

b) horizontal axis rotor with several rotor blades;

c) rotor bearing separate from or integrated into the gearbox;

d) generators driven via gearbox;

e) generators of the synchronous or asynchronous type (mostly equipped with 4-pole generator);

f) generators with only a fixed pole number or which are pole-changeable for speed adjustment;

g) output control by rotor blades (pitch or stall wind turbines);

h) generator coupled to the power grid via converter or directly.