Vibration Severity Chart
A Vibration Severity Chart is a standardized tool that maps overall vibration velocity (RMS in mm/s or in/s) to condition zones (A–D) for assessing rotating machinery health, based on ISO 10816 or ISO 20816. It helps classify machines as Acceptable, Alert, or Unacceptable for maintenance triaging.
In shop floor maintenance, engineers use vibration severity charts by first identifying the machine class (I–IV) based on rated power and shaft height, and determining foundation type (rigid vs. flexible). They measure overall vibration velocity under normal operation and plot the value on the chart to instantly classify the machine as Acceptable (Zone A), Alert (Zone B/C), or Unacceptable/Danger (Zone D). This enables efficient maintenance triaging, prioritizing machines needing immediate attention versus those suitable for long-term operation.
- Ignoring Machine Class/Foundation: Applying a generic limit like '0.125 ips is fair' to large, flexible-mounted turbines leads to false negatives where damaging vibration is overlooked.
- Using Displacement Instead of Velocity: Monitoring low-speed motors with displacement charts without accounting for frequency causes misdiagnosis, as severity standards are velocity-based for most industrial rotating equipment.
- Neglecting Trending Over Single Points: Relying on a single 'Zone B' reading to shut down a machine without observing trend progression results in unnecessary downtime instead of scheduled maintenance.
Why did ISO 10816 become ISO 20816?
ISO 10816 was split and updated to ISO 20816 (series) to better distinguish between machine vibration (ISO 20816-1) and shaft vibration (ISO 20816-2), providing more granular criteria for specific equipment types.
What is the difference between Zone B and Zone C?
Zone B indicates the machine is acceptable for long-term operation, while Zone C signifies elevated vibration requiring investigation and short-term operation only before failure risk increases.
Can vibration severity charts diagnose specific faults (e.g., unbalance vs. misalignment)?
No; severity charts are condition indicators for overall health, not fault diagnostics; specific fault identification requires spectrum analysis to identify frequency components, as the chart only provides a single RMS value.