Fluke 8024B - Page 46

8024B
2-66.
Three
resistance
ranges
have
a
high
enough
open
circuit
voltage
to
turn
ona
silicon
junction.
These
ranges
-
2
kQ,
200
kN,
and
20
MQ.-can
be
used
to
check
silicon
diodes
and
transistors.
The
preferred
2
kQ
range
is
marked
with
a
diode
symbol.
The
2002,
20
kQ
and
2000
kQ
ranges
can
be
used
to
make
in-circuit
resistance
measurements.
Typical
full
scale
voltage
and
short
circuit
current
for
each
resistance
range
is
given
in
Table
2-4.
All
values
shown
are
referenced
to
the
COMMON
input
terminal;
i.e.,
the
V/Q/S
terminal
is
positive.
NOTE
Any
changes
(greater
than
one
or
two
digits)
in
apparent
resistance
when
test
leads
are
reversed
may
indicate
either
the
presence
ofa
diode
junction
or
a
voltage
in
the
circuit.
CAUTION
Turn
test
circuit
power
off
and
discharge
all
capacitors
before
attempting
in-
circuit
resistance
measurements.
Table
2-4.
Voltage/Current
Capability
of
Resistance
Ranges
FULL-SCALE
SHORT
CIRCUIT
VOLTAGE
(TYPICAL)
CURRENT
(TYPICAL)
+800
mV
+0.12
yA
+200
mV
+0.12
pA
+800
mV
+12
uA
+200
mV
412
yA
HAV
+1.0
mA
+55
mV
+0.3
mA
2-67.
APPLICATIONS
2-68.
The
test
applications
described
in
the
following
paragraphs
are
suggested
useful
extensions
of
the
8024B
measurement
capabilities.
However,
they
are
not
intended
as
the
equivalent
of
manufacturer’s
recommended
test
methods.
They
are
intended
to
provide
repeatable
and
meaningful
indications
which
will
allow
the
operator
to
make
sound
judgments
concerning
the
condition
of
the
device
tested;
1.e.
good,
marginal,
or
defective.
2-69.
THERMOCOUPLES
2-70.
Introduction
2-71.
In
1821,
Seebeck
found
that
when
two
dissimilar
metals
are
connected
at
two
junctions
and
the
junctions
are
at
different
temperatures,
a
current
will
flow
in
the
loop
(Figure
2-18,
Part
A)
and
will
continue
to
flow
as
long
as
there
is
a
difference
in
temperature.
This
principle
is
used
by
your
8024B
when
making
temperature
measurements.
2-72.
The
K-type
thermocouple
that
is
used
with
your
8024B
is
made
from
two
dissimilar
metals,
Chromel
and
Alumel.
As
long
as
the
same
two
types
of
metal
are
used
throughout
the
loop
(Figure
2-18,
Part
B),
there
are
still
only
two
junctions.
The
copper
conductors
of
2-29