CEMB USA N500 - Manual (Page 78)

B - 2
Evaluation criteria
EVALUATION CRITERIA BASED ON THE SPEED OF
VIBRATION MEASURED ON FIXED PARTS
For almost all machines, the measurement of the total speed of vibration as RMS value on
fixed parts of the structure is able to characterize the machine from the vibratory point-of-
view.
The total value is calculated in the frequency range 10 to1000 Hz or else, for slow machines
(< 600 RPM) in the range 2 to 1000 Hz. Reference is made to the max. speed on the
support in the three directions of measurement.
The class to which the machine under test belongs is identified with the aid of Table A.
The graph of page B-3 provides a direct evaluation of the vibratory state, e.g. if the
vibration measurement on the support of a grinding machine (class 1) is 5 mm/s (RMS)
evaluation is: the vibration is not admissible, hence its cause should be investigated and
removed.
The criterion based on the speed is valid for frequencies lying between 10 Hz and 400 Hz.
Under the frequency of 10 Hz it is possible to have incorrect evaluation because the
vibrations, although having permissible speeds, would have prohibitive amplitudes of
displacement.
With frequencies below 10 Hz, it is necessary to consider the criterion based on the
displacements; while for frequencies exceeding 400 Hz, sometimes also in the range from
300 to 400 Hz, evaluation ratings based on speed should be considered with precaution,
because at such frequencies certain phenomena assume a different aspect and it is
necessary to take into account the energy radiated in the surrounding environment as well
as the vibrations of the building or the environment (ships, aircraft, vehicles) and of the
human physiological interferences. For high frequencies, measurements of acceleration
could prove useful.
The classification of Table A and the acceptability values given in the graph are partially in
agreement with ISO 10816. The ISO standard does not contemplate classes V and VI;
moreover it makes reference to specific standards either already published or due for
publication regarding every type of machine (electric motors, hydraulic machines, gas
turbines, etc.).