Basic Block Diagram - Fluke 8010A Instruction Manual

THEORY OF OPERATION
CIRCUIT DESCRIPTIONS
opposite polarity
is
used
to
discharge the
capacitor.
The
time
it
takes for the capacitor to discharge
is
measured.
The discharge time
is
proportional
to
the
level
of
the
unknown
input voltage.
This
method
is
extremely
accurate,
fast,
and
noise-free.
3-13.
In the following description of dual slope
integration,
assume
that
your instrument has a
line
power
frequency of 60
Hz
and a range has
been
selected
which
causes the
±2V
measurement range
of the Digital
Voltmeter
to
be
activated.
Figure
3-2 contains a
simplified
schematic of the
A/D
Converter and a timing
diagram.
The
circled
switches
(in
the simplified
schematic) represent
FET
switches operated
by
the
digital
controller.
These
FET
switches,
and
the three
operational
amplifiers, are
located
inside
U3. All other
components
are external to U3.
The
timing
diagram shows
the
operation of the
FET
switches for
one conversion
cycle
with
unknown
voltage inputs
at
1
/
2 range,
full range,
and
overrange.
The
conversion
cycle repeats continuously.
3-14.
The
basic
clock frequency
is
produced by dividing
the 3.84
MHz
output
from
the quartz crystal
by
64,
to
produce a clock frequency of 60
kHz.
The Timing
diagram
shown
in
Figure
3-2
is
based
on
the
number
of
clock cycles
counted
and
uses
them
as
timing
indicators.
The conversion
cycle
is
20,000 cycles
long
(or
1/3 of a
second for the
60
Hz
versions).
FUNCTION
SWITCHES
RANGE
SWITCHES
v/kn/s
CONDUCTANCE
CONDITIONER
RESISTANCE
CONDITIONER
VOLTAGE
CONDITIONER
LOW
CURRENT
CONDITIONER
DECilVIAL
POINT
A/D
CONVERTER
TRUE RMS
CONVERTER
COMMON
INPUT
SIGNAL
CONDITIONERS
Figure
3-1.
Basic Block Diagram
3-2