Machine Guard MG4-REF11 A
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SPM Instrument AB
• Box 504 • SE-645 25 Strängnäs • Sweden
Technical data are subject to change without notice.
Tel +46 152 225 00 • Fax +46 152 15075 • [email protected] • www.spminstrument.com
ISO 9001:2000 certified © SPM 2017-09. 71947 B
Machine classes
Generally, a large machine with much power is allowed to vibrate more than a smaller machine
with less power (A). Given two identical machines, there will be a considerable difference in their
vibration depending on the foundation: a comparatively weak metal frame allows more movement
than a stiff concrete foundation (B).
The international standards group industrial machinery into six different vibration classes, depend-
ing on machine size and function plus the stiffness of the foundation:
I
Parts of engines and machines, e.g. electrical motors up to 15 kW.
II Medium size machines without special foundations, 15 to 75 kW.
Rigidly mounted machine up to 300 kW.
III Large prime movers and machines on rigid and heavy foundations.
IV Large prime movers and machines on soft foundations.
VI Machines and mechanical drive systems with reciprocating masses, machines with rotating
slack coupled masses (beater shafts), vibrating screens and vibration inciters.
Motor power and types (electric, turbine, diesel), machine size and foundation stiffness (concrete
base, metal frame, etc.) will give a first indication of machine class. Most smaller process pumps
in a chemical plant would be Class II. A 100 kW ventilation fan on a concrete base would be Class
III. However, the same fan fastened to the metal deck of a ship could be considered as Class IV.
The diagram shows the limit values for all six ISO vibration classes. For each class, the standards
give vibration severity levels ranging from very good condition through average and poor to bad.
From one limit value to the next value above, vibration severity increases 1.6 times (1 step). From
one condition zone to the next above, vibration severity increases by a factor of 2.6 (2 steps). 3
steps up is a fourfold increase.
Class Class Class Class Class Class
Limit
mm/s
RMS
Vibration classes depend on machine size and function plus
the stiffness of the foundation
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