Skewness
(Index 4491-4494)
Skewness
is a statistical measure that indicates the asymmetry of the signal’s scatter
around its mean value. A change in
Skewness
indicates a fundamental change in the
mode of vibration.
Kurtosis
(Index 4495-4497)
Kurtosis
is a dimensionless parameter for the distribution of values in the acceleration
signal. The value can be used to estimate the type of vibration measured and thus
detect a change. For example, a white noise signal has a
Kurtosis
of 3, whereby a sine
wave has a
Kurtosis
of 1.5. An example is shown in
, where pulses occurring in
the vibration are reflected in higher values of
Kurtosis
.
1
2
(m/s
2
)
(S)
Figure 6: Kurtosis
1
Kurtosis = 7
2
Kurtosis = 3
Peak to peak
(Index 4498-4500)
The
Peak to peak
value indicates the range of raw acceleration and speed values. It is
calculated as the difference between the largest and the smallest value.
Shape factor
(Index 4501-4503)
The
Shape factor
is defined as the ratio between the effective value of the signal and
the mean value of the absolute values of the signal. An increase in the
Shape factor
indicates an increase in the amplitudes of harmonics in the signal.
Crest factor
(Index 4504-4506)
The
Crest factor
is defined as the ratio of the
Peak to peak
value to the RMS value of the
signal. An increase in the
Crest factor
typically indicates the occurrence of pulsed signal
components.
Impulse factor
(Index 4507-4509)
The impulse factor is the ratio of the
Peak to peak
raw values to the mean value
of the “Absolute raw values.” The value can be considered an indication of whether
brief pulses occur in the acceleration signal which are significantly stronger than the
permanent vibration.
For example, a pure sine wave has a impulse factor of 1.44. If a much stronger impulse
factor is measured for an expected sinusoidal vibration, this is an indication of pulsed
faults.
PRODUCT DESCRIPTION
4
8028041/2022-08-16 | SICK
O P E R A T I N G I N S T R U C T I O N S | MPB10
17
Subject to change without notice
