RLV-5500 Rotational Vibrometer - Theory

Tutorial PDF "Basics of Rotational Vibration Sensing"

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How a Rotational Vibrometer Works

The Rotational Vibrometer uses two parallel laser beams which exit the sensor's front lens and strike the rotating surface. Each back-scattered laser beam is Doppler shifted in frequency by the surface velocity vector in the beam direction.

This velocity is made up of rotational and lateral components. Raw velocity information from each beam is independently sent to the Controller for processing. Using a simple geometric relationship, the difference of the two velocity components is a direct measure for the pure rotational velocity of the object and eliminates lateral vibrations.

 

The advantage of Polytec’s dual interferometer approach lies in optical gain that is orders magnitude higher than designs using only interferometer operating in an optically differential mode. The resulting high optical sensitivity allows measurements on poorly reflecting surfaces, thereby increasing the range of applications and ease of use. For measuring positive negative rotations as well as vibrations around zero RPM, a Bragg cell is incorporated into the dual interferometer. The Bragg cell produces a constant angular velocity offset by frequency shifting the laser beams.