Theory Of Operation; Introduction; Overall Functional Description - Fluke 8600A Instruction Manual

8600A
Section 3
Theory
of
Operation
3-1.
INTRODUCTION
3-2.
The
theory of operation
for the
Model 8600
A
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