Operating
Jnstr
MAKING
MEASU
piom
EMEMS
CIRCUIT
I
SENSE
terminals for
4
WIRE
&wire
resistance
measurement only.
/
Figure
2-10.
Measuring Current
While an offset is enabled, the
8840A
indicates
arn
over-
range condition if either of the following conditioqs
occur:
The input signal is overrange
The calculated reading is overrange
For example, suppose the iWrument is in the 20V range
of the VDC function and you store
an
offset of +1h. The
maximum positive voltage reading that
can
be
+played
without overranging is +4.9999V, which is actually a
+19.9999V input signal. The maximum
reading that
can
be
displayed without
-19.9999V, which is actually
a
-4.9999V
can
measure
a
greater range of
higher range.
When
in autorange, the
8WA
selects the range appro-
priate for the input signal, regardless of any stored offset.
If, for example, a +10V offset is stored, and a +lVinput is
applied, the
8&40A
will autorange to the 2V r
display
an
overrange condition since it cannot
dig;
-7;
on the 2V range. Manual rhge control could
be
used to
lock the
8840A
into the 2OV range in this
caw.
Applications of the offset feature include correding for
test lead resistance in 2-wire resistance measuAements,
nulling offset currents or voltages, measu~g voltake devi-
ations, and matching resistors.
2-30.
EXTERNAL CLEANING
WARNING
TO
AVOID
ELECTRIC
SHOCK
OIR
INSTRUMENT AGE, NEVER
G@
WATER CASE. TO AVO~D
INSTRUMENT DAMAGE, NNER
APPbY
SOLVENTS
TO
THiE
INSTRUMENT.
-
Should the
8840A
case
require cleaning, wipe the instru-
Figure
2-9.
Measuring Voltage and Resistance
ment with
a
cloth that is lightly dampened with wqter or
a
mild detergent solution.
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