Fluke 8021B - Resistance; Continuity

8021
B
2-39
Full-scale
burden
voltage
(voltage
drop
across
the
fuse and
current
shunt)
for ail
ranges
except
2000
mA is
less
than
300
mV. The
2000
mA
range has a
full-scale
burden
voltage of
less
than
900
mV.
These
voltage
drops
can
affect
the
accuracy
oi
a
current
measurement,
if the
current
source is
unregulated and
the
shunt
plus fuse
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
2-12. This
error
can
be
minimized by
using
the highest
current
range
that
gives
the
necessary
resolution.
For
example, if20
mA is
measured on
the
2000 mA
range
the
burden
voltage is
approximately 5
mV
.
2-40.
Resistance
2-41.
Six
direct
reading
resistance
scales
are
provided on the 802!
B: 20 Mfl,
2000 kft,
200
kfl, 20
kfl,
2 kfl
and 200ft.
All
scales
employ
a
two-wire
measurement
technique. As a
result,
test
lead
resistance
may
influence
measurement
accuracy
on the
200fl 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
measurement
reading.
The error
is
generally
on
the order
of 0.2
to 0.3
ohms for a
standard
pair of test
leads.
2-42.
Three
resistance
ranges
(2
kft, 200
kft, and
20 Mfl)
have a high
enough
open
circuit
voltage to
turn on a
silicon
junction.
These ranges
can be
used
to check
silicon
diodes and
transistors
The 2
kfl
range is
preferred
for
this
function and is
marked with a
diode
symbol.
On
the
three
alternate
ranges
(200ft,
20 kft,
and
2000 kft),
the full
scale
voltage is
not
high
enough
to
turn a
silicon
junction
on. Use
these
ranges to make
in
circuit
resistance
measurements.
Maximum
full
scale
voltage
and short
circuit current
for each
resistance
range is
given in
Table
2-3. All
values
shown are
referenced
to the
COMMON
input
terminal;
i.e.,
the
V/fl
terminal
is
positive.
MOTE
Any
change
(greater
than
one or
two digits
)
in
apparent
resistance
when test
leads
are
reversed
may
indicate
either the
presence
of
a diode
junction
or a
voltage
in the
circuit.
CAUTION
Turn test
circuit
power
otf and
discharge all
capacitors before
attempting in-
circuit
resistance
measurements.
2-43.
Continuity
2-44. Audibly
confirmed
continuity
measurements
may
be
made using any
of the
resistance
or
conductance
ranges.
The
2
kft range
is
recommended
for
this
mode since it
provides the
lowest
resistance
threshold,
approximately
110 ohms.
On this range a
measured
resistance
lower
than 110
ohms
initiates
the
audible
tone. To
determine the
exact
threshold,
use a
variable
resistor
and
note the
display
reading
at
which the tone
switches
on
and/or off.
2-19