Overall Vibration
How is RMS calculated for Overall Vibration?
RMS (Root Mean Square) is the square root of the mean of the squares of instantaneous vibration values, providing a stable energy average unlike peak values which can be skewed by transient spikes.
Why is Overall Vibration insufficient for diagnosis?
It provides a single scalar value instead of a spectrum; while it detects that a fault exists, it cannot identify what the fault is without frequency decomposition.
What is the relationship between Peak and RMS?
For a pure sine wave, Peak = √2 × RMS; however, in complex machinery vibration, the Derived Peak may differ significantly due to non-sinusoidal waveforms.
When should a technician move from Overall to Spectral Analysis?
When the Overall Vibration trend shows a consistent increase or exceeds the Alert threshold per ISO 10816, indicating an evolving fault that requires frequency-specific identification.
Overall Vibration is the total vibration energy measured as a single, global value across a specified filtered frequency bandwidth, representing the sum of all vibration components from every part of the machine. It is typically expressed in units such as velocity (mm/s RMS), displacement (µm Peak-to-Peak), or acceleration (g True Peak).
In shop floor maintenance, Overall Vibration serves as a Level 1 screening metric to rapidly identify developing faults or trend machine health degradation over time without immediate spectral analysis. It is measured at critical bearing locations and compared against severity criteria standards like ISO 10816 or API 610 to determine if equipment is in an acceptable, alert, or failure condition. In CMMS systems such as ServiceGrid, it is trended as a key indicator to trigger maintenance work orders when values exceed predefined alarm thresholds.
Masking Specific Faults: Relying solely on the overall value fails to isolate root causes like unbalance versus misalignment because it averages all frequencies, preventing precise corrective action.
Ignoring Frequency Range Limits: Measuring overall vibration outside the machine's specific operating frequency band yields inaccurate good readings despite active failure.
Neglecting Trending: Treating a single reading as pass/fail without tracking the slope of increase; a sudden rise often indicates imminent catastrophic failure even if the absolute value is within acceptable limits.