PRÜFTECHNIK VIBXPERT II - Modal Analysis - Two-Channel Impact Test; ODS - Operating Deflection Shape; Excitation with Impulse Hammer; A. Selecting the Task and Starting the Measurement

5-27
VIBXPERT II 05.2012
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 re-
corded at multiple measurement locations during operation and set
in relation to a reference measurement location. The individual vibra-
tion 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. im-
pulse hammer) and the structural response is measured with a vibra-
tion 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 measure-
ment. 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
closes.
• 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
previous section).
Connect the impulse hammer with
the force sensor to channel B, and
Example of an ODS animation:
Maximum displacement of a mounting
platform .
* additional information are available on
request.
Measurement tasks
Selecting the measurement task and
starting the measurement
Modal / ODS