What it is
ISO 20816 is the international standard series for measuring and evaluating machine vibration. It merged two older families — ISO 10816, covering measurements on non-rotating parts such as bearing housings, and ISO 7919, covering relative shaft vibration measured with proximity probes. They were merged because real machines are assessed with both at once.
How it works
Evaluation rests on two criteria. Criterion I sets absolute limits, placing a machine in zone A (newly commissioned), B (unrestricted long-term operation), C (unsatisfactory for continuous running) or D (severity likely to cause damage). Criterion II tracks change instead: a shift equal to a quarter of the B/C boundary is significant even when the machine still sits deep inside zone A. Part 3 covers industrial machinery above 15 kW running between 120 and 30 000 r/min — pumps, fans, compressors, electric motors.
Where it stops
The series is an acceptance and severity standard, not a diagnostic one. It reports broadband RMS velocity, so an incipient rolling-element bearing defect living above 2 kHz barely moves the number. A machine can sit comfortably in zone A with a bearing weeks from failure. Envelope analysis, shock pulse methods and order tracking close that gap, and they belong to ISO 13373 rather than here.