Dear All;

What is
1) Relative shaft vibration Measurement ?
2) Absolute Shaft Vibraton Measurement?

http://www.reliabilitydirect.com/appnotes/cvr.html

Relative - if you mount a non-contacting proximity probe on the casing or a stationary part adjacent to the bearing and read shaft motion that is a relative motion. The observed motion is the shaft relative to the casing or bearing.

Absolute - if you can establish the motion of the casing, perhaps via a velocity transducer integrated to displacement, and that transducer is very near the relative transducer mentioned previously, you can vectorially sum the casing motion and the shaft relative and come up with shaft absolute.

John from PA

I generally use shaft relative as: relative to its original reading to see if position has changed from its original position in its bearing. Typically DC component to find postion and AC to find motion or vibration.