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eration overall value for this example); edit task name and
time to measure; delete selected measure task; save any
changes made to the selected measure task
Note: Different tasks will have different task details.
Characteristic overall vibration values
These values are used to evaluate machine, bearing and gear conditions. A good indicator of
the vibration forces acting on a machine is the effective value (RMS) of the vibration velocity in
the frequency range 10 - 1000 Hz or 2 - 1000 Hz. Evaluation criteria of the permissible vibra-
tion levels are specified in the ISO 10816-3 norm.
The highest signal amplitudes as peak values (0-peak, peak-peak) are recorded and used to
calculate the crest factor.
Crest factor is the ratio of the highest amplitude to the effective RMS value of a vibration and is
a measure of the intensity of the impacts in the form of a vibration. Crest factor is used to
identify wear in roller bearings and gearing mechanisms, and cavitation. A harmonic vibration
of amplitude 1 has 0.707 as its effective value and a crest factor of 1.41. If the crest factor is
higher than 1.41, impacts with higher amplitudes occur.
Shock pulse
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 dam-
age), both expressed in logarithmic [dB] terms. Bearing condition is determined by comparing
normalized signal levels and their difference with reference values.
Carpet and maximum values are affected by e.g. rolling velocity (i.e. bearing size and rpm),
signal damping, and lubrication. To evaluate the condition of the bearing and allow comparison
between values measured on different bearings, a comparison measurement in the good con-
dition or a normalization of the measured values is required.
Normalization — The bearing size and RPM are combined to give the initial value = dBi
VIBXPERT 3
to: view selected task details (characteristic accel-
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