decay time
in
the
"Hold"
position
is
<0.05
dB/sec. A typical decay
time
vs
temperature
curve
is
shown
in
Fig.4.22.
c::
]
.....
c::
!9
§ 1000
(.)
'
~
C1)
E
i=
"
~
!\...
~
100
C1)
0
10
-20
-10 0
"
~
~
'"'
~
10
20
30
40
so
Temperature (°C)
Fig.4.22. Typical decay characteristics
of
the
"Hold"
circuit
4.11. PEAK DETECTOR CIRCUIT
/69/31
It
can be seen from Fig.4.16
that
the
response of
the
RMS
detector
to
a
step function depends
upon
its principle
of
operation and
upon
the
time
constant
of
its averaging circuit. If
the
time
constant
is
reduced
then
the
output
voltage will reach its maximum value
in
a shorter time. Similarly, it
can be seen from Fig.4.18,
that
for a very
short
time
constant, E
2
will be
zero and E
1
will be equal
to
KV
1
.
This means
that
if
the
averaging
time
constant
is
made small enough
the
circuit will
act
as a peak detector. This
is
the
principle
of
operation of
the
detector
in
its
"Peak
Hold"
mode.
The
time
constant
is
approximately
10
JJSec.
which gives
the
detector
a capabili-
ty
of
recording peak values of impulses with
duration
as short as
20
J.Lsec.
If measurements
of
very
short
impulses are not required
then
the
time
constant of
the
rectifier may be easily given a higher value by increasing
the
44
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