Free Engineering Tool #019
Vibration Evaluation Zones A/B/C/D
Evaluate machine vibration severity per ISO 20816-1. Select machine group, enter measured vibration, and get the zone classification with recommended actions.
Results
| Zone | Boundary | Description |
|---|
Zone Evaluation Concept
ISO 20816-1 provides general guidelines for evaluating machine vibration by comparing measured vibration values against zone boundaries. The standard defines four zones:
- Zone A — Vibration of newly commissioned machines typically falls within this zone
- Zone B — Machines with vibration in this zone are normally considered acceptable for unrestricted long-term operation
- Zone C — Machines with vibration in this zone are normally considered unsatisfactory for long-term continuous operation; remedial action should be taken at the next convenient opportunity
- Zone D — Vibration values within this zone are normally considered severe enough to cause damage to the machine
Vibration Measurement
The primary measurement parameter is vibration velocity in mm/s RMS (root mean square), measured on the bearing housing in the frequency range 10–1000 Hz. This parameter has been shown to correlate well with machine condition for most rotating machinery.
Zone Boundaries by Machine Group
| Zone Boundary | Group 1 Large rigid | Group 2 Medium rigid | Group 3 Pumps | Group 4 Large flexible |
|---|---|---|---|---|
| A/B | 2.3 mm/s | 1.4 mm/s | 2.3 mm/s | 3.5 mm/s |
| B/C | 4.5 mm/s | 2.8 mm/s | 4.5 mm/s | 7.1 mm/s |
| C/D | 7.1 mm/s | 4.5 mm/s | 7.1 mm/s | 11.0 mm/s |
ℹ️ Note: ISO 20816-1 provides general guidelines. For specific machine types, refer to the dedicated parts: ISO 20816-2 (steam turbines >40 MW), ISO 20816-3 (industrial machines 15 kW–50 MW), ISO 20816-4 (gas turbines).
⚠️ Important: Zone boundaries are guideline values. Machine-specific acceptance criteria may be defined by the manufacturer. Always consider trending — a significant increase in vibration may warrant investigation even if the absolute level is within Zone B.
ISO 20816-1 defines four evaluation zones for assessing machine vibration:
- Zone A — Vibration of newly commissioned machines. Excellent condition.
- Zone B — Acceptable for unrestricted long-term operation.
- Zone C — Not suitable for long-term operation. Plan remedial action at the next convenient opportunity.
- Zone D — Dangerous vibration levels that may cause damage. Immediate shutdown or corrective action required.
Machine groups are defined by power rating and foundation type:
- Group 1 — Large machines over 300 kW on rigid foundations (e.g., large motors, generators)
- Group 2 — Medium machines 15–300 kW on rigid foundations (most common industrial motors and pumps)
- Group 3 — Pumps including multistage, vertical, and special-purpose pumps
- Group 4 — Large machines over 300 kW on flexible (soft) foundations
If unsure, Group 2 is a conservative default for most medium-sized industrial machinery.
Velocity (mm/s RMS) is the standard and preferred parameter for vibration evaluation per ISO 20816-1. It correlates well with vibration severity across the typical frequency range of 10–1000 Hz.
Displacement (μm peak-to-peak) is more useful for low-speed machines (<600 RPM) where velocity values may be very small but displacement is significant. It is also used for shaft relative measurements on machines with fluid-film bearings.
Zone C means the machine is not suitable for long-term continuous operation. Recommended actions:
- Investigate root cause — check for unbalance, misalignment, bearing wear, looseness, resonance
- Increase monitoring frequency (daily or continuous)
- Schedule corrective maintenance at the next planned opportunity
- The machine may continue operating for a limited period while preparing for repair
- If vibration is trending upward toward Zone D, consider immediate action
ISO 20816 is the modern replacement for ISO 10816. Key differences:
- ISO 20816-1 replaces ISO 10816-1 with the same zone boundaries and methodology
- The new numbering reflects consolidation of the ISO 20816 series
- ISO 20816 includes updated guidance on shaft vibration measurement alongside bearing housing vibration
- The evaluation zone concept (A/B/C/D) remains identical
For practical purposes, the zone limits are the same and both standards can be used interchangeably.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and vibration analyzers. Evaluate machine condition on-site per ISO 20816. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
