The above equations apply to IEPE compatible accelerometers. Accelerometers with charge output are
calculated in the same way with charge amplification G
q
in mV/pC and the charge transfer factor B
qa
of
the transducers in pC/ms
-2.
.
Example:
With an accelerometer which has a sensitivity of B
qa
= 5 pC/ms
-2
, the velocity should be measured. The
M72 operates with a charge amplification of G
q
= 100 mV/pC. At the output a voltage of
u
out
= 300 mV
RMS
arises. How great is the measured velocity v?
Solution:
v
=
300
100
⋅
5
⋅
10
=
6
mm
/
s
eff
The sensitivity settings (see Chapter 6) of the M72Ax and M72S1 instruments are also applied to the in-
tegrators.
At frequencies above 15.92 Hz the integrators generate smaller signal amplitudes due to their damping
behavior. As a result of this the
modulation declines, as does the signal-to noise ratio. As a guide value
single integration should only be applied to frequencies up to 1000 Hz, and double integration up to
200 Hz.
For frequencies below 15.92 Hz, added gain occurs. In the case of double integrators this can be up to 12
times and cause the amplifier output to overload.
Overload may occur if there are larger signal components at high frequencies
.
Despite the fact that the
output voltage is not overloaded as a result of integrator damping, the integrator input can nevertheless
overload.
The integrator frequency response curves are shown in Figure 6.)
12
Figure 6: Frequency Response of the Filters and Integrators
0,1
1
10
100
1000
10000
100000
1000000
0,001
0,01
0,1
1
10
100
HP 0.1Hz
HP 3Hz
LP 0.1kHz
LP 1kHz
LP 10kHz
LP 50 kHz
Single Int.
Double Int.
Frequency [Hz]
A
m
pl
itu
de