Although
not visible in Hi Res,
the exponent remains in
effect; care
should
be exercised when interpreting readings.
To avoid
confusion, remember
that an exponent in the
exponent display will always have its own polarity
sign; a
high
resolution digit will not.
2'25. Input Terminals
2-26.
TERMINAL INTERCONNECTIONS
2-30.
Correct use of
the 8502A’s guard terminal will
both protect the
instrument
and
provide
more accurate
readings. Since the
LO to GUARD maximum voltage rating
is
127V, the
guard
terminal
should always be
connected
either to the INPUT LO terminal
or to a point in the source
circuit to be measured. For accurate readings,
connect the
guard to minimize
common mode currents flowing through
any resistance which helps determine
the
voltage
being mea-
sured. See Figure
2-3, for su^ested guard connections.
2-27.
For dc
voltage
measurements,
both INPUT HI
terminals
may
be left
strapped together, The INPUT
LO
terminals may likewise remain
strapped. For most mea-
surements,
it
is sufficient to strap GUARD to INPUT
LO.
Refer
to Figure 2-2, for
recommended input terminal
strapping.
CAUTfOIM
The guard terminal should
not be left dis-
connected. Instrument damage can
occur if
common
mode voltage exceeds the LO to
GUARD maximum
voltage rating
(127V).
Figure
2-2.
Front
Panel
Terminal
Interconnections
2-28. GUARDING
2-31. Generally, guarding
should be used in the following
situations:
I
.
When long signal leads are
used.
2-29. Common mode voltages, resulting
from currents
and voltage
drops
between two points otherwise electrically
common, may produce
significant
errors. Proper use of a
floating, guarded
voltmeter
will minimize these errors and
allow representative reading of normal mode voltages (actual
source voltage and noise).
2. When signal source impedance is
high.
3. When making measurements
near
high-level
radi-
ated no^e, particularly at
the power line fre-
quency.
4. When making
floating measurements.
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