Calculation of the impulse factor: IF = maximum value/mean value of the absolute raw
values
1
2
Figure 7:
Impulse factor
example
1
IF = 4.2
2
IF = 1.44
4.3.6
Vibration in the frequency range
Vibration data in the frequency range in many cases allow for a much more precise
identification of vibration causes than the previously discussed time range values.
For this purpose, the vibration signal is transmitted from the time to the frequency
range by means of FFT (
Fast Fourier Transformation
). The information of what are the
dominant frequencies in a vibration makes it possible to better understand the cause
of the vibration. For example, the vibration of an motor always contains vibrations with
frequencies corresponding to the motor speed, but can also contain vibrations caused
by the motor bearings or electronic components such as the rectifier, which contain
other frequencies.
The acceleration or speed spectrum of the vibration can be observed through the
frequency.
The analysis in the frequency range is based on the vibration values of one axis or
the sum signal of all 3 axes (magnitude). The selection is made via the settings of
the vibration analysis (
see "Settings for vibration analysis (Index 4477, 4479, 4482,
).
The settings for trigger, block length and number of blocks for averaging have the
same effect on vibration analysis in the frequency range. The bandpass filter must
also be taken into account, which can restrict the frequency range under consideration
between 0.78 and 3,200 Hz.
The frequency resolution is calculated with 1 / block length in seconds. It specifies
both the smallest measurable frequency and the minimum frequency spacing that
two vibration components must have in order to be distinguishable in the frequency
analysis.
Table 6: Block length in relation to frequency resolution
Block length [ms]
Resolution [Hz]
Smallest measurable frequency
20
50
40
25
80
12.5
160
6.25
4
PRODUCT DESCRIPTION
18
O P E R A T I N G I N S T R U C T I O N S | MPB10
8028041/2022-08-16 | SICK
Subject to change without notice
