Vibration in machines is affected by their orientation and the way they are suspended. A vertical pump will vibrate differently than a horizontal pump. The horizontal pump’s movement may be restricted in the vertical direction as compared to horizontal. Vibration levels in horizontal and vertical directions are not expected to be equal. If we measure and plot the displacements taken in horizontal and vertical directions, we find that the orbit plot is not round, egg shape. We call it an anisotropic system.
A vertical pump, on the other end is more likely to have equal vibration level in the radial and tangential (the two horizontal directions), unless the movement is restricted in some way. We call it an isotropic system.
It is recommended to collect as many axes of vibration data as possible. We can learn more about a system by analyzing the data in different directions and planes. Single and triaxial transducers can used to measure vibration levels. Of course, multiple tests can be made to confirm a diagnosis.
Anisotropic systems, for example: a horizontal pump have different resonant frequencies in horizontal and vertical directions. This is due to stiffness difference in those two directions. Lower stiffness has a lower resonant frequency. Therefore, it is very important to take into account machine orientation to design a system.