वाइब्रेशन इवैल्युएशन जोन A/B/C/D

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.