Vibration Source

Exciting Frequency

Dominant Plane

Amplitude

Envelope Characteristics

Comments

Angular Misalignment

1X, 2X

axial

steady

narrow band

Most misalignment is a combination of parallel and angular.

Parallel Misalignment

1X, 2X

radial

steady

narrow band

On long coupled spans 1X will be higher.

Combined Angular & Parallel

1X, 2X

radial, axial

steady

narrow band

Misalignment is also indicated by multiples of 2X

Cocked Bearing

2X, increased 1X, and bearing tones

radial, tangential, axial

high, steady

narrow band

Usually accompanied by axial components.

Misaligned Impeller

2X, increase in vane rate harmonics

radial

steady

narrow band

Usually accompanied by low axial amplitudes.

Gear Misalignment

Strong gear mesh rate

radial, tangential, axial

steady

Usually 1X sidebands around gear mesh rate

Harmonics of gear mesh are common