PRÜFTECHNIK VIBXPERT II - Cepstrum Analysis; User-Defined Measurement Quantities

5-19
VIBXPERT II 05.2012
Measurement tasks
Cepstrum analysis
A cepstrum is the 'spectrum of a spectrum' and is particularly suitable
for detecting regular structures in a frequency spectrum. Above all,
in the case of complex patterns with many harmonics and sidebands
- that frequently occur if roller bearings or gearings are damaged- a
cepstrum simplifies the evaluation of the measurement data.
User-defined measurement quantities
As well as measurement tasks with fixed specified measurement quan-
tities, VIB XPERT provides measurement tasks where the measure-
mentquantitiescanbefreelydened.Thevoltage(±30V,AC/DC)or
current(±30mA,AC/DC)canbeconnectedasaninputsignaland
recorded as an overall value, as a time waveform* or as a spectrum*.
The assignment of the input signal to the measurement quantity is
specified by the 'Measurement quantity' and 'Unit' parameters in the
transducer setup (see P. 2-20).
Examples of user-defined measurement quantities:
- Measurement of the pressure as a current level  (4-20mA, DC).
Connection to pressure transmitter.
- Measurementoftheow rate as a current or voltage signal (4-
20mA / 0-10V, DC). Connection to flow rate measuring device.
- Measurement of the sound pressure as a time signal or spectrum.
Connection to a microphone.
- Displacementmeasurement(inductivesensorVIB6.640).
Only the following cables can be used as sensor cables:
VIB5.433-Connectioncableforlowvoltagesignals
VIB5.434-Connectioncableforlowcurrentsignals
AC overall DC overall
Sensor parameters for
sound pressure measurement
VIB 5.433 /
VIB 5.434
Pressure
Flow rate
Attention!
AC time AC Spectrum
waveform
* DC measurement for time waveform,
spectrum, see page 5-30.
Cepstrum