PRÜFTECHNIK VIB 5.300 EX Series, Operating Instructions Manual

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5-27
VIBXPERT 11.2010
Modal analysis - two-channel impact test
The two-channel impact test is used to visualize the dynamic
behavior of a structure and to detect operating-critical natural
vibration forms.
ODS - Operating Deflection Shape
To record the vibration modes of a structure, the vibrations are
recorded at multiple measurement locations during operation and set
in relation to a reference measurement location. The individual
vibration modes can be calculated from the relative amplitudes and
phase differences of the measurement locations to the reference and
can be displayed as an animation*.
Excitation with impulse hammer
If the structure is excited with a suitable excitation source (e.g.
impulse hammer) and the structural response is measured with a
vibration sensor, the resonance frequency can be calculated.
The described measurement methods are implemented in the follow-
ing measurement tasks:
- ODS
The sensor on channel B records the 'excitational' force and serves
as the reference point for all other measurement locations. The
sensor on channel A is attached to the designated measurement
locations of the structure in sequence and records the respective
structural response.
- Impact test with impulse hammer
This measurement task is similar to the one-channel impact test;
channel B records the excitation and is the trigger for the
measurement. To take measurements on a running machine, the
'negative average' averaging procedure is available.
A. Selecting the task and starting the measurement
• Select the task icon 'Modal analysis' (see above).
• Press the F key to open the task
selection window.
• Click on the respective task (ODS
or Bump test with impulse ham-
mer). The selection window clos-
es.
• Click again to start the measure-
ment.
The measurement procedure with
the
impulse hammer is essentially
identical to the one-channel impact
test: excitation, measurement, re-
cording of result - excitation, mea-
surement,..., end result (see also pre-
vious section).
Example of an ODS animation:
Maximum displacement of a mounting
platform .
Measurement tasks
Selecting the measurement task
and starting the measurement
* additional information are available
on request.
Modal / ODS
F