5-18
VIBXPERT 11.2010
Measurement tasks
Envelope analysis
Envelope analysis is a proven method for detecting periodic impacts
in the vibration signal of a machine. It is mainly used for the
diagnosis of roller bearing damage and tooth damage and is based on
the demodulation of amplitude modulated vibration signals.
Periodic impact sequences in a component excite high frequency
machine resonances that serve as a carrier signal of the low frequency
impact signal. To separate the low frequency modulation from the
high frequency resonance, the signal is filtered with a highpass filter,
rectified and then filtered using a lowpass filter. Consequently, the
remaining signal consists of the modulation signal only - the so-called
'envelope' - from which the FFT of the envelope frequency spectrum
can be calculated.
VIBXPERT saves the envelope time signal filtered last together with
the envelope frequency spectrum.
To display the time signal, press the MENU key and select 'Info /
Time signal' (see below).
VIBXPERT provides two methods for calculating the envelope:
Highpass and lowpass filtering is carried out on the basis of hardware
or software.
In the case of hardware filtering, the signal is processed in a filter
chip. This method is identical to that used in the VIBSCANNER FFT
data collector and, hence, is suitable for comparison measurements
with both devices.
Software filtering, on the other hand, calculates the envelope with
the aid of an algorithm. This method is more flexible that the
hardware-based method and offers more filter combinations.
Note
Envelope spectrum for
roller bearing analysis
Envelope spectrum for
gearing analysis
Left:
Measurement setup
for envelope spectrum
Right:
Envelope spectrum and
appropriate time waveform
Summary of Contents for VIB 5.300 EX Series
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