12
the machine or the structure.
The instrument measures the total RMS vibration value in the
frequency range. This RMS value is the average sum of all
the measured vibrations. In the actual frequence range.
CALCULATION:
If the simultaneous vibration caused by unbalance is (4mm/s),
by misalignment (2 mm/s) and by the gear mesh (5 mm/s),
then the total vibration measured on the VIBER X2 is 6.7
mm/s.
6.1 ISO standard 10816-3
The ISO standard classifies the machines differently if the
machines are flexible or rigid. This reflects the location of the
machine’s stiff-body resonance related to the basic
running speed of the machine.
For example, a machine supported by rubber or springs has a
resonance at low running speeds. The machine starts vibrate
at low RPM. When the speed is
increased above the resonance
frequency, the vibration is redu-
ced. This machine is considered
flexible.
Resonance is easily found when
a flexible machine is running up
or down in speed. The reso-
nances are located at the RPM
where the vibration has a local
maximum level. Modern machi-
nes that have high RPM’s and
Total vibration
(RMS)
=
4.1
ISO standard 10816-3
The ISO standard classifies the machines differently if the machines are flexible or
rigid. This reflects the location of the machine's stiff-body resonance related to the
basic running speed of the machine.
For example, a machine supported by rubber or springs have a resonance at low
running speeds. The machine starts vibrate at a low rpm. When the speed is increased
above these resonance frequencies, the vibration is reduced. This machine is
considered flexible.
Resonance is easily found when a
flexible machine is running up or
down in speed. The resonances are
located at the rpm where the
vibration has a local maximum
level.
Modern machines that have high
rpm
ʼ
s and flexible bearing supports
and foundations, can be treated as
flexible, even when they aren
ʼ
t
mounted on rubber or springs.
Group 1:
Large machines with rated power above
300kW.
Electrical machines with shaft height H
> 315mm.
Operating speed ranges from 120 to
15000 rpm.
Group 2:
Medium-sized machines with a rated power above 15kW up to and including 300kW.
Electrical machines with shaft height between
160 < H < 315 mm.
Operating speed normally above 600 rpm.
Group 3:
Pumps with multi vane impeller and with separate driver with rated power above 15kW.
Group 4:
Pumps with multi vane impeller and with integrated driver with rated power above 15kW.
The ISO 10816-3 standard allows for slightly higher limits when a foundation is
considered more flexible than rigid.
A conclusion 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
.
Vibration Measurement Instruments
Our X series of hand-held instrument
VIBER X1
VIBER X2
VIBER X3
VIBER X5
Manual Viber X1_121002.indd 2
10/3/12 9:26 AM
Total vibration (RMS)
= √4
*
4+2
*
2+5
*5 = 6,7 mm/s
