11
Vibration Measurement Instruments
Modern machines often run at high speed and bearing-supports
are fl exible, foundations should/can be evaluated as fl exible, even
when it is not mounted on rubber or springs.
The ISO 10816-3 standard allows for slightly higher limits when
a foundation is considered fl exible than when if it is rigid.
A conclusion from this is also that a resonance condition in
principle is not allowed or at least must be avoided at operating
speeds. In practice this also includes the double speed as well as
any other natural excitation frequency such as blade passage etc.
A great advantage with proper vibration measurements and the
use of vibration standards is that you can judge the future
maintenance cost reliably already at fi rst start-up. If you fi nd
levels above 3 mm/s RMS, you can be rather sure that the machine
will cause increased activities in maintenance.
The specifi c cost and action is of course individual to the
machine design.
The next logical step is therefore to apply more advanced
analyzers like VIBER X2™, X3™ or X5™ to learn the frequency
behind the vibration and thus the exact mechanical fault.
The practice of this is beyond the scope of this manual.
Manual Viber X1_121002.indd 11
10/3/12 9:26 AM
Group 3
:
Pumps with multivane impeller and with separate driver with
rated power above 15kW.
Group 4:
Pumps with multivane impeller and with integrated driver
with rated power above 15kW.
Modern machines often run at high speed and bearing-
supports are flexible, foundations should/can be evaluated as
flexible, even when it is not mounted on rubber or springs.
The ISO 10816-3 standard allows for slightly higher limits
when a foundation is considered flexible than rigid. A conclu
-
sion from this is a resonance condition should not be allowed
or at least must be avoided at operating speeds. In practice,
this also includes the double speed as well as any other natural
excitation frequency such as blade passage.
A great advantage with proper vibration measurements and
the use of vibration standards is that you can judge the future
maintenance cost reliably at start-up. If you find levels above
3 mm/s RMS, it’s a risk that the machine will have higher
maintenance cost. The specific cost and action is specific to
the machine design.
The next logical step if you want to improve the accuracy of
measurements is to use more advanced analyzers like VIBER
X2™, X3™ or X5™ to learn and detect the frequency behind
the vibration and thus the exact mechanical fault. The practice
of this is beyond the scope of this manual.
