Radio Shack 22-174A - AC;DC Current Measurement Procedure; Measurement Steps and Notes

3. Remove
power
from
the
circuit
under
test. Then
break the
circuit
at the
appropriate
polnt.
Connect the
probes
in
series with
the circuit.
Test Unlt
Sorles Connoctlon
5. Apply
power
to the
circuit.
\
f
lf
the
current is
less
than
the maximum
shown for
the input
jack
selected,
the meter
might
down-range
for a higher
resolu-
tion
reading.
For
example, if
your
measure
a 3500
pA
current
a.n!
the
curent
changes
to 350
pA,
the
meter
automatically
shifts
to the 400.0
pA
range
if
the meter
is in the
auto mode.
Notes:
lf
you
set the
meter for
DC
current, the minus
(-)
sign
ap-
pears
or disappears
to
the left of
the bargraph
to sho^/
the
polarity
of the measured
current.
The
400
mA
and
the
4000
pA
ranges
are
fuse-protected.
The
10A
range is
not fuse-protected.
The
meter
displays
the
overrange indication
or 0 il it
blows
a fuse
while measuring
current.
lf
the meter
displays
the overrange
indication wnen"$ou
measure
AC
current, and
the circuit
does
not
exceed
the AC
current
in the
present
range,
the
circuit
is
exceeding the
meter's
DC rating.
For
example,
if
you
try to measure
a DC
power
supply's AC
riple
currenl, the
signal has
both an AC and DC
compo-
nent.
lf
the DC
component
exceeds
the
meter's
rating,
the
meter
displays
the overrange
indication. To
measure
this
current,
you
must
externally
block
the DC component.
The
AC current
modes
do not
use an AC coupling
capacitor
to block DC.
Both DC
and
the
AC
current flows
through
the
shunt resistance.
Too much
DC current
overpowers
the AC
component.
lf
you
need
to measure
the AC component
of
a
DC
signal,
we
suggest
you
use a
highquality
capacitor
to
block
the DC
component. For
normal AC line
frequencies,
we
suggest
you
use a .47
pF
or
larger
capacitor rated
lor
the vottage
involved
(500
volts
or
greater).
l.
I
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