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.

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