How do I know if my rotors are out of balance?

There are two ways to detect the unbalance in rotors.

Way-1: Just by measuring the vibration amplitude on the bearing housing using vibration meter.

1. Note the running speed of equipment from the electric panel or VFD.
2. Note the peak vibration velocity amplitude and its corresponding displacement.
3. Since we know that the unbalance defect occurs at a frequency of 1× Running speed, using the following relations calculate the frequency. Since unbalance is a harmonic excitation, following relations can be used.

Where

a. velocity (mm/s) is 0 to Peak

b. Displacement (Microns) is Peak to Peak

c. N is RPM of rotor

4. Substitute the peak vibration velocity and its corresponding displacement in the above said equation to find the N. If N matches the running speed of rotor, then it’s surely unbalance.

Way-2: Using vibration analyzer

Use any vibration analyzer, it shows the peak amplitude at a frequency of 1 × RPM as shown in figure below, then its surely unbalance.