5-25
VIBXPERT 11.2010
Measurement tasks
Impact test - 1 channel
The Impact test is used to determine the resonance frequency of a
structure. In the case of a rotating machine, it is possible to determine
the RPM ranges in which vibrations are disproportionately amplified
by resonance* and could damage the machine. These ranges must
then be avoided during operation and should be passed through as
quickly as possible during runup and coastdown of the machine.
The one-channel impact test only records the system response. The
two-channel impact test also records the excitation. Any source of
vibration that contains as many frequencies as possible is suitable for
exciting a structure - such as a pulse-blow with a rubber hammer.
• Check and change the measurement parameters, if necessary.
The measurement can take place with the machine running or at a
standstill. The signals from a running machine can be hidden
using the so-called 'negative averaging method'.
• Attach the transducer to the machine - either with a magnet or,
even better, with a screw fitting.
• Set the number of individual measurements in the measurement
setup (e.g. 2 measurements, see below).
• Start the measurement by clicking on the task icon (see above).
• When the message 'Wait for trigger' appears, excite the machine
with a suitable rubber hammer: Strike near to and in the direction
of the transducer once per measurement.
• For each single measurement, strike exactly the same location
once with the hammer.
After each single measurement, the result can be accepted or
discarded (see below). After all measurements have been completed,
the averaged final result appears together with the 10 highest
amplitudes in the spectrum.
* e.g. excited by an imbalance or
misalignment
Left:
Setup parameters for impact test
Trigger Start < 0 : Signal is also record-
ed before the excitation
Right:
Measurement after hammer strike
Spectrum with resonant frequencies
and measured time signal
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