Fluke 93 Service Manual page 49

CIRCUIT DESCRIPTIONS 3-15
I 1
Figure
3.
7
Schematic diagram
attenuator section
•
Detailed
circuit
deacription
See
figure
3.7
ar^d circuit
diagram
A2a
(figure 10.4).
input
eoupHng
The
incoming
signal
first
passes
the
AC/DC
coupling section (C2202).
When
re\ay
K2201
i$
opened,
the signal
is
AC
coupied
via
C2202.
H.F. (high
frequency) path
After
the coupling
section,
the
L.F,
pan
of
the
signal
Is
Olocked by
capacitor
C2203. Only
the H.F. part
of the input signal enters the H.F. attenuator. This
is
a
triple
capacitive
divider, consisting
of
a
1
to
100,
a
1 to
10.
and a
1
to
1.46 divider
The
1
to
1
.48
divider section
is
switched on
when
relay
switches
K2202
and
K2203
are
In
the "upper"
position (as
shown on
circuit
diagram A2a,
figure 10.5).
The
1
to
1.48
divider
cc^sists
of
C2203 and C2209
in
parallel
with
some
parasitic capacitors.
The
attenuation of
1
.48
times
in this
straight-on path
is
compensated
for later in
the
circuitry.
The
separate sections
are
switched
In
the
signal path, depending on
the attenuation
required:
Table 3.2 Sections
used
in
various attenuator
settings.
Attenuator Settings
|
Sections
Used
Attenuation
5
mV/d
iv 1
00 mV/di
1.48X 1.48 times
200 mV/div
1
V/dlv
1.48X.
10x
14.8 times
2 V/dlvIO
V/div
|
1.48x,
lOOx
148
times
20
V/dlv
1O0
V/div
i
1.48X. lOx,
lOOx
1460
times