5-27
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
following 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
hammer). The selection
window closes.
• Click again to start the
measurement.
The measurement procedure
with the
impulse hammer
is
essentially identical to the one-
channel impact test: excitation,
measurement, recording of result
- excitation, measurement,..., 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
Summary of Contents for VIB 5.310
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