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Vibration Severity & Fault Triage

Classify vibration severity per ISO 20816-3 and identify probable fault causes using VDI 3839 fault signature patterns — in a single workflow.

Tool Purpose & README

What this tool does

Enter your machine parameters, measurement context, and vibration reading. The tool returns:

  • Zone classification (A/B/C/D) per ISO 20816-3, with delta-from-baseline logic
  • Ranked fault signature matches based on VDI 3839 pattern rules
  • Follow-up measurement recommendations for each probable fault
  • Printable evaluation report

Standards scope

  • ISO 20816-3: Industrial machines, nominal power > 15 kW, 120–15,000 RPM
  • VDI 3839: Fault signatures for unbalance, misalignment, looseness, and bearing defects

Copyright note

ISO zone threshold tables are copyright ISO. This tool does not republish them. You must enter zone boundary values from your own copy of ISO 20816-3 Table 1. Placeholder default values are shown for orientation only — always verify against your standard.

Inputs

Expert Mode Bearing geometry & history
Machine Description
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Measurement
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ISO 20816-3 Zone Limits
Enter zone boundary values from your copy of ISO 20816-3 Table 1. Defaults shown are indicative — verify against your standard.
Baseline & History
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Bearing Geometry (for BPFO/BPFI/BSF/FTF)
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Enter machine parameters and press Evaluate Vibration to see results.

Probable Fault Candidates

Ranked by pattern match score. Expand each card for frequency indicators and follow-up actions.

Run evaluation to see fault triage results.

Prioritised Next Steps

    Run evaluation to see recommended actions.

Run evaluation to generate report.
Contents
  1. Overview
  2. ISO 20816 Zone System
  3. VDI 3839 Fault Signatures
  4. Bearing Defect Frequencies
  5. Limitations
  6. References

1. Overview

Vibration monitoring of rotating machinery requires answering two questions sequentially: Is the vibration level acceptable? and Why is it this high? ISO 20816 answers the first; VDI 3839 answers the second.

ISO 20816 classifies severity into zones A–D based on broadband velocity RMS. VDI 3839 maps vibration patterns (frequency, direction, amplitude) to root causes.

2. ISO 20816 Zone System

ISO 20816-3 defines four evaluation zones for broadband vibration velocity RMS (mm/s):

  • Zone A: New or recently serviced machinery — normal baseline condition.
  • Zone B: Acceptable for unrestricted long-term continuous operation.
  • Zone C: Unsatisfactory for continuous operation — short-term acceptable; investigate.
  • Zone D: Vibration severe enough to cause damage — immediate action required.
Important: Zone boundaries depend on machine group and foundation type. Always use values from your own copy of ISO 20816-3 Table 1. This tool does not republish copyrighted threshold tables.

3. VDI 3839 Fault Signatures

VDI 3839 provides diagnostic guidelines mapping vibration patterns to fault types:

  • VDI 3839-2 (Unbalance): Dominant 1× RPM in radial direction; amplitude proportional to speed².
  • VDI 3839-3 (Misalignment): Angular: high axial at 1× and 2×. Parallel: radial 2× dominant. Phase 180° across coupling.
  • VDI 3839-4 (Looseness): Sub-harmonics (0.5×) and/or many harmonics; unstable phase.
  • VDI 3839-5 (Bearing Defects): BPFO, BPFI, BSF, FTF frequencies; high-frequency acceleration elevated.
Single measurement limitation: Fault differentiation improves significantly with measurements in all three directions (H, V, axial) and phase data. A single broadband value provides plausibility ranking only.

4. Bearing Defect Frequencies

Rolling element bearing defect frequencies can be calculated from bearing geometry:

Ball Pass Frequency — Outer Race (BPFO) $$ BPFO = \frac{N_r}{2} \cdot f_s \left(1 - \frac{d_r}{d_p}\cos\alpha\right) $$
  • \(N_r\): Number of rolling elements
  • \(f_s\): Shaft frequency (Hz) = RPM / 60
  • \(d_r\): Rolling element diameter (mm)
  • \(d_p\): Pitch circle diameter (mm)
  • \(\alpha\): Contact angle (degrees)
Ball Pass Frequency — Inner Race (BPFI) $$ BPFI = \frac{N_r}{2} \cdot f_s \left(1 + \frac{d_r}{d_p}\cos\alpha\right) $$
Ball Spin Frequency (BSF) $$ BSF = \frac{d_p}{2 d_r} \cdot f_s \left[1 - \left(\frac{d_r}{d_p}\right)^2 \cos^2\alpha\right] $$
Fundamental Train (Cage) Frequency (FTF) $$ FTF = \frac{f_s}{2} \left(1 - \frac{d_r}{d_p}\cos\alpha\right) $$

5. Limitations

  • Fault scoring is based on measurement direction and bearing type only — it is a plausibility ranking, not a diagnosis. Confirmation requires spectrum analysis, phase measurement, and multiple measurement points.
  • Zone classification uses broadband velocity RMS. ISO 20816-3 may specify narrower frequency bands for specific machine types.
  • Unit conversions (displacement → velocity, acceleration → velocity) are approximate single-frequency conversions and introduce error for broadband signals.
  • ISO 20816-9 (gear units) and ISO 20816-8 (reciprocating compressors) have their own scope and limits — this tool applies ISO 20816-3 heuristics only for those machine types.

6. References

  • ISO 20816-3: Mechanical vibration — Measurement and evaluation of machine vibration, Part 3: Industrial machines with nominal power above 15 kW and nominal speeds between 120 r/min and 15 000 r/min.
  • VDI 3839-2: Instructions for measuring and interpreting vibration on machines — Unbalance.
  • VDI 3839-3: Instructions for measuring and interpreting vibration on machines — Misalignment.
  • VDI 3839-4: Instructions for measuring and interpreting vibration on machines — Looseness.
  • VDI 3839-5: Instructions for measuring and interpreting vibration on machines — Rolling element bearings.
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