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Gain
20
dB
Preamplifier
- - - - Included 100
pF Ace.
Cap.
Included 200
pF
Ace. Cap.
10 dB
0 dB
. . . . . . . v
/
v
/
..,..,
...
-1
0 dB
..,,
..,,
..,.
~·
,...
-20
dB
0.01
0.02
/
/ "
~
..,
~
_...
:;......
F""' " "
..,!..""
~o-'
,..
~· ......
..,.
,..
I-'"
0.05
Ma
x.
l
sensitLty
,.,....
~
-
... -1 ...
...
-·-
.
,.....,..
~-
.....-
~
_...
~
,'
,,
...... ~-
,.,,..
_
i.o"' .....
~-"'""
~~
,'
..,.
,...
"""
·'~
. .
,..·'.
Min. sensitivity
~-
...
~--
~·-:;r
....
-
..........
,
,
,.
,..·'
...
...
.,.·
.~
_,.•"'
0.1
0.2
0.5
Fig.5.4. Low frequency response of the preamplifier (without integration
networks) with and without accelerometer capacitance included
From equation 5.1 it can be seen that if the resistance R
1
and the
capacitance
Cc
is high, then the lower cut off frequency of the preamplifier
will be low.
When an accelerometer is employed with the 4292 (see Fig.5.5) the
effect of the accelerometer capacitance
CA
and the capacitance
CL
of the
connecting cable must also be considered. In this case the accelerometer
capacitance is shunted by the cable capacitance
CL
and the coupling
capacitance
Cc
in series with the input resistance R
1 .
Therefore if the react-
ance of
Cc
is small compared to
CA
(i.e.
Cc ~CA)
the output from the
2T~~tlt7
Fig.5.5. Equivalent circuit of preamplifier input including capacitance of
accelerometer and connecting cable
24
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