MD-03Machinery Diagnostics

Vibration Severity Zones

Classify broadband machine vibration into evaluation zones A–D (ISO 10816 style).

Measurement

Machine class / group

Input as

Broadband velocity

mm/s

Velocity RMS

3.2mm/s

Evaluation zone

Margin to B/C

-0.4mm/s

Margin to C/D

3.9mm/s

Zone C - unsatisfactory for long-term continuous operation. Plan remedial action at the next opportunity.

Severity chartmm/s RMS, 10–1000 Hz

§ Theory of operation

Broadband velocity as a severity measure

Between roughly 10 Hz and 1 kHz, the RMS vibration velocity measured on bearing housings correlates well with the dynamic stresses in a machine and its risk of damage. ISO 10816 (now being replaced by the ISO 20816 series) defines four evaluation zones for this broadband value:

A - new machines
B - unrestricted long-term operation
C - limited period operation, plan correction
D - vibration likely to cause damage

Classes and groups

The general guidance of ISO 10816-1 (Annex B) sorts machines into four classes by size and foundation. ISO 10816-3 refines this for industrial machines above 15 kW, separating Group 1 (large, > 300 kW) from Group 2 (medium) and rigid from flexible supports. A foundation is “flexible” when the lowest natural frequency of the machine–support system is below the main running frequency.

\begin{aligned} &\text{Zone boundaries step by } {\approx}\,1.6{\times}\ \text{(4 dB):} \\ &\text{0.71 – 1.12 – 1.8 – 2.8 – 4.5 – 7.1 – 11.2 – 18 mm/s RMS} \\ &v_\mathrm{rms} = v_\mathrm{peak}\,/\,\sqrt{2} \qquad 1\ \text{in/s} = 25.4\ \text{mm/s} \quad \text{(sine assumption)} \end{aligned}

Using zones wisely

Zone limits are generic. Trending is more valuable than absolute values: a step change of 25 % of the B/C boundary warrants investigation even within Zone B. Users should set ALARM (typically B/C plus margin) and TRIP(typically C/D) values based on machine history. Always check the current edition of the relevant part of ISO 20816 for your machine type, values here are for orientation.