Besides the frequency range of 10 to 1000 Hz, the VM25 has a further frequency
range for vibration severity measurements from 2 to 1000 Hz. This is suitable for
measurements on slow running machines with a nominal speed of less than
120 min
-1
and on reciprocating engines according to ISO 10816-6.
The corresponding VM25 frequency response graph can be viewed in Figure 4.
Vibration velocity is formed through integration of the acceleration measured by the sen-
sor. The following formula applies to sinusoidal signals:
v
=
a
2
Π
f
It is evident that in the case of constant acceleration (a) the value of velocity (v) drops at
higher frequencies (f). As a consequence the measuring range limits of the velocity mea-
surements are frequency dependent. (Figure 5).The maximum velocity measurable
with the VM25 is around 1000 mm/s (RMS). It yields a frequency independent
6
Figure 4: Frequency response curves for velocity
Figure 5: Amplitude range for velocity (RMS)
1
10
100
1000
10000
1
10
100
1000
10000
v: 2Hz – 300Hz
v: 10Hz – 1kHz
Integrator
Hz
m
m
/s
1
10
100
1000
10000
0,001
0,01
0,1
1
10
v: 10Hz – 1kHz
v: 2Hz – 1kHz
Hz
m
m
/s
