Bode and Polar Plot

Vibration Vector

•          A vibration vector plotted in the transducer response plane

•           1x vector is 90 mic pp /220^o

•           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