Page 54 - Rotating Machinery Pratical Solutions to Unbalance and Misalignment

Rotating Machinery: Practical Solutions

Figure 3-8. Beat Frequency

If a part vibrates within 10% of its natural frequency or one
of its harmonics, it may be subject to a beat frequency as well,
even though there appears to be no second vibrating source.
In general, beat frequencies can be easily detected since they
come in and out of phase, causing the vibration amplitude to in-
crease and then appear to go away. Beat frequencies can excite the
natural frequency of one another, or perhaps a third member will
go into resonance.
Careful analysis will assist in determining the best way to
eliminate problems with beat frequencies.