A practical guide to laser Doppler vibrometry measurements directly from rotating surfaces

Commercially available Laser Doppler vibrometers are typically configured with a single beam to measure radial and axial vibrations or with parallel beams to measure pitch, yaw and torsional vibrations. Provided sufficient light intensity can be collected, axial and torsional vibration measurements are relatively straightforward. Radial and pitch / yaw vibration measurements are less straightforward and rotor surface roughness or treatment is critically important. Unless rotor surfaces can be considered “polished-circular”, post-processing is necessary to remove a significant cross-sensitivity to motion orthogonal to that which it is intended to measure. This paper serves as a practical guide through the optimum configurations to be used on rotors to measure all components of vibration, including subtleties associated with beam diameter and vibration amplitude on polished rotors.