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Definition of machine classes according to ISO 2372
The following text is a quotation from ISO 2372 (1974, E, page 6, Annex A). This ISO recommendation
has also been published as British Standard (BS 4675, part I). A similar vibration classification of industrial
machinery can be found in VDI 2056.
In order to show how the recommended method of classification may be applied, examples of specific
classes of machines are given below. It should be emphasized, however, that they are simply examples
and it is recognized that other classifications are possible and may be substituted in accordance with the
circumstances concerned. As and when circumstances permit, recommendations for acceptable levels
of vibration severity for particular types of machines will be prepared. At present, experience suggests
that the following classes are appropriate for most applications.
Class I
Individual parts of engines and machines, integrally connected with the complete machine in its normal
operating condition. (Production electrical motors of up to 15 kW are typical examples of machines in
this category.)
Class II
Medium-sized machines, (typically electrical motors with 15 to 75 kW output) without special founda-
tions, rigidly mounted engines or machines (up to 300 kW) on special foundations.
Class III
Large prime movers and other large machines with rotating masses on rigid and heavy foundations
which are relatively stiff in the direction of vibration measurement.
Class IV
Large prime movers and other large machines with rotating masses on foundations which are relatively
soft in the direction of vibration measurement (for example turbogenerator sets, especially those with
lightweight substructures).
Class V
Machines and mechanical drive systems with unbalanceable inertia effects (due to reciprocating parts),
mounted on foundations which are relatively stiff in the direction of vibration measurement.
Class VI
Machines and mechanical drive systems with unbalanceable inertia effects (due to reciprocating parts),
mounted on foundations which are relatively soft in the direction of vibration measurements; machines
with rotating slack coupled masses such as beater shafts in grinding mills; machines, like centrifugal
machines, with varying unbalances capable of operating as self-contained units without connecting
components; vibrating screens, dynamic fatigue-testing machines and vibration exciters used in pro-
cessing plants.
Summary of Contents for VibChecker
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