Dear Alessandro,
As discussed in the following forum topic: Oscillation in local axial wind component and AOA, loads in the rotating frame due to yaw error, shear, turbulence etc. show up as harmonics of the rotor speed (1P, 2P, 3P, etc.), but loads in the fixed frame show up as harmonics of 3-times the rotor speed (0P, 3P, 6P, etc.).
Does your accelerometer have the bandwidth to measure 6P and higher frequencies?
Best regards,