Vibration severity evaluator (ISO 20816-3)
Enter the vibration velocity you measured on the bearing housing and see which zone (A, B, C, D) it falls in and what that means. Pick the machine group and foundation type, and edit the limits if needed.
Peak → RMS assumes a sine wave (RMS = peak × 0.707); approximate for broadband signals.
Zone boundaries (mm/s RMS)
Example values; check the current standard. Enter your own limits (e.g. from the manufacturer or in-house) if needed.
Measurement points
1 · Point 1
Enter a value.
Scale bar
ALARM / TRIP guidance
- ALARM ≈ baseline + 25% of the B/C boundary
- Enter a baseline value for ALARM.
- TRIP ≈ at most 1.25 × the C/D boundary
- 8.88 mm/s RMS
These are guidance values; each organisation sets its own alarm limits according to machine type and operating experience.
This is a preliminary evaluation; it does not replace a technical review or a declaration of conformity. Measurement location and direction, machine type (reciprocating machines, pumps and wind turbines have separate parts of the standard) and operating condition change the result. The limits are example values; check the current standard.
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How to use it
A
Choose the criterion, machine group and foundation type (or the machine class for the legacy standard).
B
Enter the value and unit for each measurement point; add points if needed.
C
Read the zone letter, its meaning and the position on the scale bar; edit the limits if yours differ.
02
What do the zones mean?
ISO 20816-3 divides the broadband velocity RMS measured on the bearing housing into four zones. A: typical of newly commissioned machines. B: normally acceptable for unrestricted long-term operation. C: normally unsatisfactory for long-term continuous operation; the machine may run for a limited period until a suitable opportunity for remedial action arises. D: severe enough to risk damage.
The zone letter is a severity indicator, not a fault diagnosis. The same value can be a familiar level on one machine and a sudden jump on another, so how the value changes over time matters at least as much as the limits.
03
Rigid and flexible foundation
The limits depend on the system the machine sits on. If the lowest natural frequency of the machine and foundation system in the measurement direction is at least 25% above the main excitation (operating) frequency, the system is rigid; otherwise it is flexible. Flexible systems tolerate higher vibration velocity for the same risk of damage.
If you do not know the foundation class, the natural frequency can be found with an impact (bump) test or a run-up/coast-down measurement. If in doubt, try both options and see which zone the result falls in; if they differ, the foundation class is decisive.
04
What does ISO 20816-3 not cover?
The standard applies to industrial machines above 15 kW running between 120 and 30,000 r/min. Machine types such as reciprocating machines, pumps and wind turbines have their own parts of the standard (for example ISO 20816-6 for reciprocating machines, ISO 10816-7 for pumps, ISO 10816-21 for horizontal-axis wind turbines with gearbox); this tool does not evaluate them.
The criterion only evaluates broadband (10–1000 Hz) velocity on the bearing housing. High-frequency or narrow-band fault signatures such as bearing defects can appear in the spectrum before this value rises, so severity evaluation should be used together with spectrum analysis. The legacy ISO 10816-1:1995 table is withdrawn and is offered for comparison only.
FAQ
- Is the data I enter sent anywhere?
- No. The calculation runs entirely in your browser; values are not sent to any server or stored.
- What is the difference between mm/s RMS and mm/s peak?
- For a sine wave the RMS value is about 0.707 times the peak. ISO 20816-3 limits are in RMS; if you measure peak, convert to RMS first. For real broadband signals the ratio can differ from a sine.
- Which frequency range should I measure in?
- For ISO 20816-3 the basis is broadband velocity RMS from 10 to 1000 Hz on the bearing housing. A meter that clips outside this range or a narrow-band value cannot be compared with the standard.
- Why can the limits be edited?
- Manufacturers, contracts or in-house standards may define different limits, and editions of the standard can change. The values in the tool are examples; check the current standard and enter your own limits if needed.
- I am in Zone C; should I stop the machine immediately?
- Zone C normally means unsatisfactory for long-term continuous operation; it does not necessarily require an immediate stop. The cause should be investigated and remedial action planned at a suitable opportunity. Machine type, trend and the manufacturer's instructions decide.
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