Which frequency is primarily associated with unbalance in a rotor?

The frequency primarily associated with unbalance in a rotor is 1X, which corresponds to the rotational speed of the rotor itself. Unbalance occurs when the mass distribution of the rotor is not uniform, leading to uneven forces as it rotates. This imbalance generates vibrations at the same frequency as the rotor's rotational speed—hence, it is classified as a 1X frequency.

When the rotor spins, any deviation from a perfect balance results in a cyclical force that operates at the same rate as the rotor's rotation. Therefore, monitoring vibrations at the 1X frequency is essential for identifying and diagnosing unbalance issues.

Other frequencies, such as 2X or 3X, may indicate other types of mechanical issues, or harmonics that could arise due to resonance or other vibration modes. However, for directly assessing rotor unbalance, the 1X frequency remains the definitive indicator.