Fluke VIB 5.310, User Manual

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5-25
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.
Almost 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 filtered
out 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 mis-
alignment
Left:
Setup parameters for impact test
Trigger Start < 0 : Signal is also re-
corded before the excitation
Right:
Measurement after hammer strike
Spectrum with resonant frequencies
and measured time signal
Impact test