91398 Rev A.1 01/16
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Total acceleration (g)
This is the RMS value of the total vibration acceleration measured by the meter over its entire frequency
range (2 Hz to 10
kHz). This reading is shown in units of g (Earth’s gravitational constant, where 1 g = 9.81
m/s
2
).
Displacement
Pressing the arrow buttons when the reading screen is displayed will display RMS displacement (thou or
mm). Press the arrow buttons again to revert to the ISO value display (mm/s or inch/s).
2.2.2 Vibration analysis
Press the down arrow to display the readings of vibration velocity (inch/s or mm/s), or
displacement (mm or thou), broken down into each of three bands.
The display shows the vibration level in frequency ranges based on multiples (1X, 2X and 3X) of the specified
machine run speed shown beneath the bars.
Note
: 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 or by using the strobe attachment.
The frequency ranges of the VA bands are based on the following multiples of running speed:
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. Large vibrations at the running speed indicate that the machine is out of balance.
Even a very well balanced machine will typically show some vibration at the running speed but the figure
should ideally be quite low (typically less than 2 mm/sec for a medium sized machine).
2X = Misalignment
A high level of vibration in the frequency band centered 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 two different centers of gravity (one from each shaft). The accelerometer picks up a peak as each center
of gravity passes by, resulting in two positive and two negative peaks each revolution of the shaft. This typically
gives rise to a vibration signal at double the running speed of the machine.
3X = Looseness
High vibration in the frequency band centered at three times running speed indicates looseness (mounting
bolts, weak foundations, etc) as it is not usual to see third order vibration in a machine unless there is structural
looseness that is being excited by the vibration of the machine.
2.2.3 Frequency spectrum
Press the down arrow button to display vibration levels as a frequency spectrum from 0 to 1 kHz.
The heights of the peaks indicate RMS vibration level (mm/s or inch/s) at each frequency
point in the spectrum.
The readings to the right of show the frequency (Hz or RPM) and the RMS vibration level
(inch/s or mm/s) at the position of the cursor (red dotted line). The cursor can be moved
with the arrow buttons.