An interesting spectrum phenomenon is often seen when measuring planetary gearboxes. Because there are multiple gears meshing at the same gearmesh frequency, there may be either constructive or destructive interference of the vibration at the sensor location.
Destructive interference can cause the gearmesh frequency and certain sidebands to vanish from the spectrum. Asymmetrical sidebands are common in this case.
Destructive interference happens when the gear teeth do not mesh at the same time. In the spectrum, the gearmesh frequency at the center has almost no amplitude, and there are asymmetrical sidebands.
