Practical Solutions to Machinery and Maintenance Vibration Problems
Chapter 7, Misalignment
Section 21, Evaluating Phase Relationships Between the Horizontal and Vertical Directions at the Same Bearing
Another way to separate the symptoms of unbalance from those of misalignment is to obtain phase readings in both the vertical and horizontal directions at the same bearing. Assuming no resonance to alter phase readings and a vibration due almost exclusively to unbalance, the phases in the vertical and horizontal directions measured at the same bearing will be approximately 90° to each other (depending on the direction of rotation or 270°). But for misalignment at most bearings of the two coupled machines, the vertical and horizontal phases are approximately 0° or 180° out-of-phase. This seems to occur in about three fourths of all bearings of misaligned machines.
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