Fluke 8024B - Page 44

8024B
4.
DC
VOLTAGE
MEASUREMENTS
Loading
Error
in
%
=
100
x
Rs—
(Rs
+
10’)
Where:
Rs
=
Source
resistance
in
ohms
of
circuit
being
measured.
9.
AC
VOLTAGE
MEASUREMENTS
First,
determine
input
impedance,
as
follows:
*
V1
+
(27
F-
Rin-
C)?
Where:
Zin
=
effective
input
impedance
Rin
=
10’
ohms
Cin
=
100
x
10
-'?
Farads
F
=
frequency
in
Hz
Then,
determine
source
loading
error
as
follows:
*
zs
Zs + Zin
Loading
Error
in
%
=
100
x
Where:
Zs
=
source
impedance
Zin
=
input
impedance
(calculated)
*
Vector
algebra
required.
Figure
2-16.
Voltage
Measurement
Error
Calculations
2-63.
Full-scale
burden
voltage
(voltage
drop
across
the
input
terminals)
for
all
ranges
except
2000
mA
is
less
than
250
mV.
The
2000
mA
range
has
full-scale
burden
voltage
of
less
than
900
mV.
This
voltage
drop
can
affect
the
accuracy
of
a
current
measurement
if
the
current
is
unregulated
and
the
DM
M
resistance
represents
a
significant
portion
(1/1000
or
more)
of
the
source
resistance.
if
burden
voltage
does
present
a
problem,
the
percentage
of
error
can
be
calculated
using
the
formula
in
Figure
2-17.
This
error
can
be
minimized
by
using
the
highest
current
range
that
gives
the
necessary
resolution.
For
example,
if
20mA
is
measured
on
the
2000
mA
range
the
burden
voltage
is
approximately
5
mV.
2-64.
Resistance
Measurements
2-65.
Six
direct
reading
resistance
ranges
are
provided
on
the
8024B;
20
MQ,
2000
kQ,
200
kQ,
20
kQ,
2
kO,
and
2002.
All
ranges
employ
a
two
wire
measurement
technique.
As
a
result,
test
lead
resistance
may
influence
measurement
accuracy
on
the
2002
range.
To
determine
the
error,
short
the
test
leads
together
and
read
the
lead
resistance.
Correct
the
measurement
by
subtracting
the
lead
resistance
from
the
unknown
reading.
The
error
is
generally
on
the
order
of
0.2
to
0.3
ohms
for
a
standard
pair
of
test
leads.
2-27