Bode and Polar Plot

Vibration Vector

          A vibration vector plotted in the transducer response plane
           1x vector is 90 mic pp /220o
           Zero reference is at the transducer angular location
           Phase angle increases opposite to direction of rotation

 Polar Plot

           Polar plot is made up of a set of vectors at different speeds.

           Vector arrow is omitted and the points are connected with a line

           Zero degree is aligned with transducer location

           Phase lag increases in direction opposite to rotation

          1x uncompensated Polar Plot shows location of rotor high spot relative to transducer

           This is true for 1x circular orbits and approximately true for 1x elliptical orbits

Bode Plot and Polar Plot Show the Same Detail

          Bode’ Plot displays the same “vibration vector data” as the Polar Plot 
           Vibration amplitude and phase are plotted separately on two plots       with speed on the horizontal axis.

Effect of Slow Roll Compensation

          Slow roll compensation removes slow roll runout from filtered vibration
            What remains is mainly the dynamic response
           Compensated vector has zero amplitude at the compensation speed

Detecting Resonance with Bode & Polar Plots

          In a Bode plot balance resonance is indicated by peak amplitude and sharp, significant change of phase at the frequency of the peak.
 On Polar plot rotor modes will produce large, curving loops.Small system resonances are more easily visible as distinctive small loops


  1. I appreciate all of the information that you have shared. Thank you for the hard work!

    - The Vibration Analysis