Misalignment means that the centre lines for two coupled axles not coincide. If the centre lines of the axles are parallel it is called parallel misalignment. If the axles meet in one point, but the centre lines are not parallel it is called angle fault. In reality misalignment faults are often a mixture of the two types mentioned.
|Source of vibration||Exciting frequency||Dominating direction||Amplitude||Spectral characteristic||Comments|
|Angle fault||1X, 2X||axial||constant||narrow band||Normally a misalignmnt is a combination of parallel and angle fault.|
|Parallel fault||1X, 2X||radial||constant||narrow band||On long connected shafts 1X will have a higher amplitude.|
|Both angle-and parallel fault||1X, 2X||radial, axial||constant||narrow band||Misalignment is also indicated by multiples of 2X.|
|Cocked bearing||increased 2X 1X, bearing frequencies||radial, axial, tangential||high, constant||narrow band||Usually also include axial components.|
|Misaligned fan wheel||2X, increased multiples on blade pass frequency||radial||constant||narrow band||Usually also include low axial amplitudes.|
|Misaligned gearbox||High gear mesh frequency||radial, axial, tangential||constant||Normally 1X sideband round gear mesh frequency||Multiples of gear mesh frequency is common.|