VIBRATIONS
The International
Standardisation Organitation, ISO, has issued international standard covering balancing and vibration characteristics. ISO 2373
is of particular interest for electric motors. It governs permitted vibration level on delivery and applies to motors
with shaft heights in the range 80 t0 400 mm. The vibration level is expressed
in mm/s rms ( milimeteres per second root
mean squared ) and must be measured at no load with the motor on elastic
mounting. ISO 2373 requires the shaft extension to be fited with a full – size
key during vibraton measurement. The requirements apply in the measurement
range 10 to 1000 Hz.
Grade
of
|
Speed
|
Maximum
Vibration Velocity in mm/s rms
|
||
quality
|
r /
min
|
at
shaft height, mm
|
||
|
|
8 -
132
|
160 -
225
|
250 -
400
|
N
|
600 ≤
3 600
|
1.8
|
2.8
|
4.5
|
Normal
|
||||
R
|
600 ≤
1800
|
0.71
|
1.12
|
1.8
|
Reduced
|
> 1 800
≤ 3 600
|
1.12
|
1.8
|
2.8
|
S
|
600 ≤
1800
|
0.45
|
0.71
|
1.12
|
Special
|
> 1 800
≤ 3 600
|
1.71
|
1.12
|
1.8
|
The
corresponding standard for large machines has not yet been issued, but a figure
of 2.8 mm/s can be taken as guide, at least for squirrel
– cage motors. Measurement with the motor bolted fast to a solid base
may occur, as may measurement with a half key fitted to the shaft extension,
the smooth shaft method.
Rotor
balancing is a relatively simple opration and the balance is easy to check.
However, the final vibration resistance is also iinfluenced by other factors,
mainly the nature of base on wich he motor is mounted, although the method of
clamping, the aligment and the electromagnetic forces also play part.
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