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accelerometer will be reduced causing a reduction in its effective voltage
sensitivity over its entire frequency range. A relationship giving the effective
sensitivity SE of the accelerometer in m V /g when loaded by cable capaci-
tance CL is:
5.2.
where
SA
is the accelerometer sensitivity in mV/g given on the calibra-
tion chart for the accelerometer,
and
C
is the cable capacitance in pF included in the calibrated sensi-
tivity SA.
The effect of CA and Cc on the lower limiting frequency of the entire
system is that their reactances will add. Consequently the low frequency cut
off of the system will occur at a higher frequency. A relationship which
enables the low frequency cut off fc
2
of the system to be calculated, is:
CA
+
CL
+
Cc
21T R
1
CA Cc
5.2.3. High Frequency Characteristics
5.3.
For the "Acceleration" mode, the high frequency characteristics of the
preamplifier for maximum and minimum sensitivity settings and various
output voltages are given in Fig.5.6. The characteristic also shows the effects
1 kHz
Ga in
20
dB
10 dB
r - - -
r - - -
Max.
sensitivity
- - --t--l.
T
"'N.
r
~
I
!
:"--,
1p<J
rr;
ca~le
1
-1d
VR~S
1
ou~put
---
3 VRMS output
10kHz
--~
------
.....
..........
....
....
~
'
0 dB
Min.
sensitivity
-....::
--
--
-
~-
.........
............
-......;;;;::
r-
Type
42r2
',
............
'
'
-10 dB
""'-
........_
I
Frequency
100kHz
~
~-
t---
---
-
....
~
r-.,
~-
....
--
~I'-
"""-
'
'
......
'
~
'
I'
',
"'-,
'
"'
!'...
'
.......
',
I"
..:_
·r-.
'
.......
~
...
........ f'.
'
t'-...
~
.......
'
·r--,
~ ~
r-..
.........
~~
~
,........_
~
.......
~,
....
........_
'
t--,h
'
['.,
-......_.....--
v
I'
I?
~
I'>
I?
'
I' >
~
1
I>
[>
>
No
ext.
cable
3 m cable
10 m cable
30m cable
VRMS output
No
ext.
cable
3 m cable
10 m cable
100 m cable
30 m cable
271002
Fig.5.6. High frequency characteristics of the preamplifier, due to load by
extension cables, at different output voltages and at maximum and
minimum sensitivity. Cable capacitance 5 nF Jm·
25
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