Illustrated Vibration Diagnostic Chart Sample
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PROBLEM SOURCE | TYPICAL SPECTRUM | PHASE RELATIONSHIP | REMARKS |
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MASS UNBALANCE
A. FORCE UNBALANCE | | | Force Unbalance will be in-phase and steady. Amplitude due to unbalance will increase by the square of speed below first rotor critical (a 3X speed increase = 9X higher vibration). 1X RPM always present and normally dominates spectrum. Can be corrected by placement of only one balance correction weight in one plane at Rotor center of gravity (CG). Approx. 0 degree phase difference should exist between OB & IB horizontals, as well as between OB & IB verticals. Also, approx. 90 degrees phase difference between horizontal and vertical readings usually occurs on each bearing of unbalanced rotor (+30degrees). |
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B. COUPLE UNBALANCE | | | Couple Unbalance results in 180 degrees out-of-phase motion on same shaft. 1X RPM always present and normally dominates spectrum. Amplitude varies with square of increasing speed below first rotor critical speed. May cause high axial vibration as well as radial. Correction requires placement of balance weights in at least 2 planes. Note that approx. 180 degrees phase difference should exist between OB & IB horizontals, as well as between OB & IB verticals. Also, approx. a 90 degrees difference between the horizontal and vertical phase readings on each bearing usually occurs (+30 degrees). |
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MISALIGNMENT
A. Angular Misalignment | | | Angular Misalignment is characterized by high axial vibration, 180 degrees out-of-phase across the coupling. Typically will have high axial vibration with both 1X and 2X RPM. However, not unusual for either 1X, 2X or 3X to dominate. These symptoms may also indicate coupling problems as well. Severe angular misalignment may excite many 1X RPM harmonics. Unlike Mechanical Looseness Type 3, these multiple harmonics do not typically have a raised noise floor on the spectra. |
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B. Parallel Misalignment |...