![background image](http://html1.mh-extra.com/html/mmf/vm25/vm25_instruction-manual_1813941010.webp)
In the case of constant acceleration (a) it is visible that the displacement value (d) de-
creases quadratically with increasing frequency (f). As a consequence the measuring
range limits of displacement measurements are strongly frequency dependent. Figure 7
shows the measurement range limits depending on frequency.
The maximum displacement of the VM25 that can be measured is around 60 mm
(RMS). It yields a frequency independent modulation range of up to 10 Hz. At higher
frequencies the measuring range limits for acceleration of around 240 m/s² take effect.
3.5. Rolling Bearing Parameters K(t)
The rolling bearing parameter, also known as the diagnosis coefficient of Sturm
K(t), is an approved parameter for the condition analysis of rolling bearings, as de-
fined in the VDI 3832 (and other guidelines). It is formed by the RMS and peak
value of acceleration at a frequency range of 1 to 10 kHz. The 1 kHz high pass filter
ensures that the rolling bearing signal is not overlapped by the vibration of foreign
mechanical parts, such as imbalances.
The K(t) value relates the currently measured RMS and peak values to the RMS and
peak values at a starting point in time as follows:
K
(
t
)=
a
rms
(
0
)⋅
a
pk
(
0
)
a
rms
(
t
)⋅
a
pk
(
t
)
within this:
a
rms
(0)
RMS for the start point in time (reference point in time)
a
pk
(0)
maximum value (peak value) for start / reference point
a
rms
(t)
current RMS
a
pk
(t)
current maximum value (peak value)
The start or reference measurement is subsequent to first-time operation of the bear-
ing. Ideally after the elapse of a certain running-in time. At this point in time the
K(t) value is 1. Following ongoing wear and tear of the machine i.e. running dam-
8
Figure 7: Frequency response curves for displacement (RMS)
1
10
100
1000
0,1
1
10
100
1000
Integratorkennlinie
d: 5Hz-200Hz
Hz
m
m