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CIRCUIT DESCRIPTION
MODEL 630 POTENTIOMETRIC ELECTROMETER
3-6.
GUARDING. Guarding
is accomplished
by floating
the null
detector
and the input
circuitry
at a voltage
equal
to the input
voltage
from a low impedance
source.
This
full
guarding
eliminates
leakage
between
the input
terminal
and ground.
Such leakage
in an
unguarded
circuit
is difficult
to avoid,
under
laboratory
conditions,
and can result
in
sizeable
errors.
of 108
For example,
in an unguarded
circuit
with
a 1-megohm source,
leakage
ohms will
introduce
1% error.
A guarded
circuit
eliminates
this
element
of error.
16
OL66R
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