© TPI Europe 2021
8 TPI 9085 User Guide V1.0
N.B. in order to perform a vibration analysis it is
important that the running speed of the machine is
entered correctly. This can be done with the
“Setup
Wizard
” as described in Section 2.3.1 of this user guide,
or by using the strobe attachment (see Section 5.1)
The frequency ranges of the VA bands are based on the
following multiples of running speed
2
:
1X = Unbalance
:
The level of vibration in the frequency band based on the running speed is usually
indicative of how well balanced the machine is. A
large
vibration at the running speed
usually indicates that the machine is out of balance. However even a very well balanced
machine will typically show some vibration at the running speed but this figure should
ideally be quite low (e.g. typically less than about 2 mm/sec for a medium sized machine).
2X = Misalignment
:
A high level of vibration in the frequency band centred at twice the running speed is a
possible indication of misalignment. This is based on the fact that shaft misalignment can
result in a double peak in the waveform due to there being two different centres of gravity
(one from each shaft). In other words the accelerometer picks up a peak as each centre
of gravity passes by and hence there will be two positive and two negative peaks each
revolution of the shaft. This will typically give rise to a vibration signal at
double
the
running speed of the machine.
3X = Looseness
:
High vibration in the frequency band centred at 3 times running speed is a possible
indication that something may be loose (e.g. loose mounting bolts, weak foundations etc.)
as it is not usual to see third order vibration in a machine unless there is some structural
looseness that is being
“excited” by the vibration of the machine.
2.2.3 Frequency spectrum
Pressing the down arrow button once more brings up
a display similar to that shown opposite, where the
vibration levels are shown as a frequency spectrum in
the range from 0 to 1kHz.
The heights of the peaks indicate the RMS vibration
level (in mm/s or inch/s) at each frequency point in the
spectrum.
2
Multiples of running speed are sometimes referred to as “orders”
