Instruction manual

Vibration acceleration a (without integration):
a=
u
out
G⋅B
ua
(a in m/s²; u
out
in mV; G in mV/mV; B
ua
in mV/ms
-2
)
Vibration velocity v (single integration):
v=
u
out
G⋅B
ua
⋅10
(v in mm/s; u
out
in mV; G in mV/mV; B
ua
in mV/ms
-2
)
Vibration displacement d (double integration):
d =
u
out
G⋅B
ua
⋅100
(d in µm; u
out
in mV; G in mV/mV; B
ua
in mV/ms
-2
)
The equations above apply for IEPE compatible accelerometers. For accelerometers with charge output,
G is replaced by the selected charge amplifier range in pC/g and B
ua
is replaced by the transducer’s char-
ge sensitivity B
qa
.
Example:
Vibration velocity is measured using an accelerometer with a sensitivity of B
qa
= 5 pC/ms
-2
. The M68 is
operated in the range G=100 mV/pC. Its output voltage is 300 mV
rms
. What is the corresponding vibrati-
on velocity?
Solution:
v=
300
100⋅5
⋅10=6 mm/ s
RMS
Often a direct connection between the output voltage of the M68 and the measured physical
quantity (for example “1 mV corresponds to 1 mm/s”) is desired.
This can be achieved by adjusting the connected measuring equipment or by typing in a correction factor
in a PC based data acquisition system. In the example given above this correction factor would be 0.02.
At higher frequencies the output voltage will have only small amplitudes after integration. The dynamic
range and the signal-to-noise ratio therefore become lower in the kHz-range (Figure 8).
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