3-24
VIBXPERT 11.2010
Options
Note
NUMBER OF LINES (SPECTRUM, CEPSTRUM): Number of lines displayed.
Together with the 'upper frequency', this parameter specifies the
resolution of the spectrum (Δf).
W
INDOW (SPECTRUM, CEPSTRUM): In the measurement of periodic signals,
there are time data sets with periodic gaps as a result of the finite
observation period. Thus, the frequency lines appear wider in the
corresponding spectrum. The window functions suppress these
'side lobes'.
Window features:
Hanning: Standard for FFT. Frequency precise, but amplitude
errors (<15%); for the analysis of continuous processes with
high frequency resolution and lowest possible break-off effect.
Rectangular: Frequency errors, but amplitude is precise; suitable
for the analysis of individual pulses, particularly if the pulse is at
the beginning of the time window.
Kaiser: As with Hanning, but lower amplitude errors (<12%)
F
lat-Top: Lower frequency accuracy than Hanning, amplitude more
precise. For precision amplitude analysis of continuous processes.
Hamming: Frequency errors as in Rectangular; amplitude errors
(18%) less than in Rectangular, but higher than in Hanning.
Bartlett: Next to Rectangular, this is the simplest window (trian-
gle); lower amplitude and frequency accuracy.
Blackman: As for Hanning, but with higher frequency accuracy;
amplitude errors as in Kaiser (12%); next to Kaiser, the second
best alternative for nearly all applications.
A
VERAGING TYPE/ NO. OF MEASUREMENTS (SPECTRUM, TIMEWAVEFORM, CEPSTRUM)
Without av.: During the measurement each recorded spectrum is
displayed. The 'Number of averages" specifies how many single
measurements are carried out.
Linear: The individual spectra are added and divided by the
number of averages. This averaging type emphasizes recurring
stationary sections in the spectrum.
Peak-hold: Highest measurement value is displayed. This type of
averaging emphasizes peaks that occur stochastically.
Exponential: Individual measurements are exponentially averaged
(the last spectrum is given the highest weighting).
Time-synchronous: The individual measurements are averaged on
an RPM synchronous basis. Reference transducer required.
O
VERLAP (SPECTRUM, CEPSTRUM): See section A1, P. 3-21.
M
EASUREMENT RANGE: See section A1, P. 3-22.
T
RIGGER TYPE / LEVEL / START (SPECTRUM , CEPSTRUM, TIMEWAVEFORM)
See section A1, P. 3-22
B. Setup parameters for sensors
The transducer parameters to be set up are described on P. 2-20. If
you have defined a default transducer for vibration measurements
(see p. 2-22), the ‘Sensor Setup’ menu is deactivated.
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