Use The ProcedureUnload the analyzerChoose a machine for analysisCarefully identify the run speed (you may have to check the velocity readings for this)Start at the motor free end in EnvelopingLook for bearing frequencies and other cause of IMPACTIVE vibration for example - looseness

Continue the ProcedureCheck the velocity spectrumLook for dynamic defects such as imbalance, misalignment & loosenessCheck the time waveform of the velocity reading to confirm impactive vibrations (in Gs)Check the time waveform of the HF reading to confirm dynamic vibrations (in mm/s)Check the High Frequency (HF) reading if you suspect electrical vibration such as rotor bars.

BearingsAs a rule of thumb:FTF or Cage Run speed x 0.43Outer race Run speed x No. elements x 0.4Inner race Run speed x No. elements x 0.6

Bearings (contd.)Remember:Enveloping is NOT direction specificElectrical frequencies are multiples of 7,200 cpmDo not confuse speed harmonics with defect frequenciesEnveloping time domain is USELESS for analysis

Typical fault spectra (Enveloping)Outer race defect:BPFO Run speed x No. elements x 0.4Fundamental frequency will be dominantWill usually have many harmonicsWill NOT have sub-harmonicsWill usually not have side-bands Fault amplitudes will be above 0.2 G

Outer race defect example

Outer race defect exampleHigh Frequency AccelerationTime - GsTime - mm/s

Typical fault spectra (Enveloping)Inner race defect:BPFI Run speed x No. elements x 0.6Fundamental frequency will be dominantWill usually have many harmonicsWill NOT have sub-harmonicsWILL have side-bands of run speedFault amplitudes will be above 0.1 G

Inner race defect example

Confirm with HF & waveform

Typical fault spectra (Enveloping)General bearing defects:Brinelling (true or false) will give sidebands of FTF (cage) around BPFO or BPFIIf there are no spikes but a general rise in carpet level then there is a lubrication problemCarpet level will rise as lubrication deteriorates and/or damage worsens

Dynamic Defects (Velocity)General dynamic defects:ImbalanceMisalignmentLooseness Gearing defectsMotor defects

Dynamic Defects (Velocity)General dynamic defects:Imbalance - a large spike at run speed with no other significant spikes in the spectrum. Shows best in velocity mm/s.Usually only significant on machines which have heavy wear or suffer fouling (such as fans).Fans do not usually need rebalancing if the imbalance is less than 6 mm/s at run speed.

Example of imbalance - spectrum

Example of imbalance - waveform

Dynamic Defects (Velocity)Misalignment:High axial vibration compared to radial.Usually accompanied by up to 3 harmonics of run speedShows best in velocity mm/s.Belt driven machines may have one component aligned to the belts and other component misaligned!Realign the machine if the maximum vibration due to misalignment is over (about) 4 mm/s.

Example of misalignment - spectrum

Example of misalignment - time waveform

Dynamic Defects (Velocity)Looseness:Many harmonics of run speed. Run speed is not always dominant. Often impactive so shows in velocity spectrum, time domain (Gs) and in EnvelopingIn extreme cases will show sub-harmonics

Example of looseness - spectrum

Example of looseness - waveform

Dynamic Defects (Velocity)Gear defects:Up to 4x fundamental gear-mesh.Multiple harmonics of gear-mesh indicates excessive backlash in the gears. (note does not show when the gear is permanently loaded on one side Sideband delta frequency indicates speed of the shaft which has broken/damaged teeth or an eccentric gear.Maximum amplitude @ Gear-mesh should be no more than 1 mm/s RMS.

Example of a gear defect

Example of a gear defect

Summary

Dominant Frequency

Secondary Frequency

Harmonics of Dominant Frequency

Sidebands

Dominant Direction

Defect

Suggested Maximum Amplitude @ Dominant Frequency

1x

Nil

Nil

Nil

Radial

Imbalance

6 mm/s

1x

1/2 x

Multiple

Nil

Radial

Looseness

3 mm/s

1x

3x

2 or 3

Nil

Axial

Misalignment

4 mm/s

BPFO / BPFI

1x

Multiple

1x / Cage

Radial

Bearings

0.5 mm/s

7,200 cpm

Rotor Bar

2 or 3

2xLF of RBF

Any

Electrical

5 mm/s

Any

Any

Nil

Nil

Any

Resonance

7 mm/s

Gear Mesh

1x

3 or 4

1x

Radial

Gearing

1 mm/s

2x Belt

1x

2 or 3

N/A

Radial

Belts

5 mm/s