PRÜFTECHNIK VIBXPERT II - Shock Pulse Measurement; Normalization; Normalization Adjustment

5-2
VIBXPERT II 05.2012
Shock pulse measurement
Shockpulse signallevels areindicated asacombination of'Carpet
value' (background level, indicative of lubrication condition) and
'Maximum value' (transient peak level, indicative of damage), both
expressed in logarithmic [dB] terms. Bearing condition is determined
by comparing normalized signal levels and their difference with refer-
ence values.
These characteristic overall values are typically affected by various
external factors (e.g. rolling velocity, i.e. bearing size and rpm, signal
damping, lubrication). To evaluate the condition of the bearing objec-
tively and to allow comparison between values measured on different
bearings requires either a comparison measurement in the good con-
dition or a normalization of the measured values.
Normalization
This process considers the following individual factors:
- Bearing size, RPM
These bearing-specific factors are combined in the so-called ‘ initial
value’ or the ‘dBi value’. The dBi value is calculated from the rota-
tional speed and the bore diameter of the bearing.
-Signaldamping,lubrication,load,...
These unspecific external influencing factors must be determined
empirically within the framework of a ‘normalization adjustment’. To-
gether with the dBi value, the ‘adjustment value’ obtained in this way,
or even the dBa value, results in the so-called ‘adjusted initial value’
(dBia value).
Consequently, the normalized shock pulse value (dBn) works out to:
dBn = dBsv – dBi – dBa = dBsv – dBia
Normalization adjustment
Under ideal conditions (dBa=0), the normalized carpet value of a
bearingingoodconditionequals5dBn.The‘true’dBavalueequals
the dif ference from the measured value, only with the initial value
(dBi) normalized carpet value.
Example
Normalized measurement on a new bearing: 9 dBn.
The adjustment value is therefore:
   9dBn-5dBn=4dBa.
The procedures used for bearing
diagnosis (shock pulse, envelope curve,
vibration acceleration) comply with the
ISO norm, 10816-1 (Appendix E3 , E1).
Measurement tasks