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C.3 'Phase - RPM' measurement type
This type of measurement records the phase amplitude and the
phase angle in dependence on the RPM. Points of resonance are
indicated by RPMs with increased amplitude and a simultaneous
jump in phase angle by (ideally) 180°. The results are displayed
either in a Bode diagram or in a Nyquist diagram.
Bode diagram
The upper curve shows the amplitude progression and the phase is
displayed in the lower screen. The Zoom function applies to both
diagrams.
If the 'Continuous Phase' option in the display setup is enabled, a
number of dotted horizontal lines may appear in the phase diagram
under certain circumstances. These lines represent the '360° - 0°'
transition that can occur any number of times due to the constant
continuation of the phase progression (see P. 4-19, 5-6)
Nyquist diagram
This type of diagram displays the locus (amplitude and phase) of the
curve in polar coordinates (see below).
Changing the type of diagram
Press the F key and select the type of diagram.
Averaging cancellation if rpm deviation > 10%
VIBXPERT records a time signal block per shaft rotation and
combines multiple blocks to an average signal, depending on the
averaging number. If the rotational speed varies by more than
10% during averaging, VIBXPERT aborts the averaging and uses
the averaged signal to calculate the amplitude and the phase
angle. These values are only saved if the rpm deviation set in the
measurement setup is reached.
Measurement tasks
Note
Runup / Coastdown:
Left:
Phase - RPM (Bode diagram)
Right:
Phase - RPM (Nyquist diagram)
5-9
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