Fluke 8600A - Section 3 Theory of Operation; 3-3. OVERALL FUNCTIONAL DESCRIPTION

8600A
Section
3
Theory
of
Operation
3-1.
INTRODUCTION
3-2.
The
theory
of
operation
for
the
Model
8600A is
arranged
under
two
major headings.
The
first,
titled
OVER-
ALL
FUNCTIONAL
DESCRIPTION,
discusses
the overall
operation
of
the
instrument
in
terms
of
the
functional
re-
lationships
of the
major
circuits.
The
second
section
is
titled
CIRCUIT
DESCRIPTION
and
deals
with
the in-
ternal
operation
of
each major
circuit
in more
detail.
Block
diagrams
and
simplified
circuit
diagrams
are
included
in
these
sections.
The
complete
schematic
diagrams
are lo-
cated in Section 8 of this manual.
3-3.
OVERALL
FUNCTIONAL
DESCRIPTION
34.
Introduction
3-5.
The
8600A circuitry
can
be divided
into three
major
sections.
The first
of the
three
sections,
termed In-
put
Signal
Conditioners,
(see Figure
3-1) comprises
the
In-
put
Divider,
Ohms
Converter,
AC
Converter
and
Current
Shunt.
The second
section
is
the
A/D
(analog-to-digital)
Converter
and the
third
is the
Control
and
Display
section.
The
basic
operational
relationship
of
these functional
areas
will
be
discussed
in the
following
paragraphs.
3-6.
Input
Signal
Conditioners
3-7.
The
term,
input signal
conditioner,
describes
the
basic
function
of the
four
subsections
grouped
under
it.
The
input
divider,
current
shunts,
ohms
converter,
and ac
converter
provide
the
A/D converter
with
a dc
analog volt-
age
representative
of
the input
(ac volts,
dc
volts, ac
cur-
rent,
dc
current,
or
resistance)
applied
to the
instrument.
The
path
that
each
input signal
follows
as it
is conditioned
for
the
A/D
converter
is illustrated
in
Figure
3-1
.
3-8.
DC voltages
applied
to
the
input terminals
are
directed
via
function
switch
contacts
directly
to
the A/D
converter
in the 200
mV
and 2V
ranges
but to the
in-
put divider
in
higher
ranges.
The
input divider
divides
it
by
10,
100 or 1000
in
the
20,
200 and
1200 volt
ranges
respectively.
The
A/D
converter
is provided
with
a
dc voltage
level,
representing
full
scale,
of 200 mV
for
the
200
mV range
and two
volts
for
the 2V
through
1200V
ranges.
3-9.
An
ac voltage
input
to the
instrument
is applied
through switch
contacts
to the
ac converter.
The converter
then
changes the
ac input
to
an equivalent
dc voltage
for
the
200 mV
and 2V
ranges.
In
the 20 V
through 1200
V
ranges
the
feedback
within
the ac converter
is
changed by
reed
relays so
that the
dc voltage
output to the A/D
converter
is two
volts
for
a full
scale indication
on the
20 V
and 200 V
ranges
and
1
.2 volts on the
1
200 V
range.
3-10.
When
making
a resistance
measurement
the un-
known
resistance,
connected
across the
input,
is supplied
with
a known value
of current
by the ohms converter
and
input divider.
The
voltage
drop
across the unknown
resistance
is then
applied to
the
A/D converter
as
a
direct
representation
of
that
resistance.
The input divider
is
used
to change
the
amount
of current
applied
to
the
un-
known
resistance
when
different
ranges are selected.
3-11.
When
making
current
measurements
(ac or dc)
the
unknown
current
is
applied
directly, via the MA
INPUT
terminals,
to the
current
shunt. The unknown
current
is directed,
via
the range
switch contacts,
through
a
precision resistor
network
so that
the voltage developed
1/77
3-1