Distortion; Noise - BRUEL & KJAER 4292 Instructions And Applications

5.2.6. Distortion
The amount of non-linear distortion produced by the preamplifier in its
"Acceleration" mode is shown in Fig.5.13. From this it can be seen that the
amount of distortion produced is not only dependent on the output voltage
from the preamplifier, but also by the sensitivity of the preamplifier, which
is determined by the amount of negative feedback applied using the SENSI-
TIVITY control. Therefore to avoid distortion greater than 1%, the maxi-
mum output voltage for minimum and maximum sensitivity settings of the
preamplifier should not be allowed to exceed 14 V peak or 17 V peak
respectively.
10
~
8
c
0
: i
6
0
Q)
Cl
~ 4
c
~
Q)
a...
2
0
0
5
10
15
Output Voltage (Vpeak)
. I
Max1mum s.n,;t;v;7
(+
21 dB
Minimum
Sensitivity
(-1 dB)
~
J
I
_)_,)
20 21
.1.7'/'rf/A'l-
Fig.5.13. Preamplifier distortion for maximum and minimum sensitivity
settings
5.2.7. Noise
The total noise produced by the preamplifier is influenced by both the
SENSITIVITY and AMPLITUDE control settings of the 4292. With the
AMPLITUDE control set to "Off", the total noise produced over the 20 Hz
to 20kHz range for maximum and minimum preamplifier sensitivities is
approximately 20 JJ.V and 60 JJ.V respectively. With the AMPLITUDE con-
trol set to its extreme clockwise position the total noise produced is 25 JJ.V
and 65 JJ.V respectively. These noise figures apply for the input of the pre-
amplifier terminated with a 1 nF capacitor.
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