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OPERATION
HOODELS 610B,
610BR ELECTROMETERS
2.
The full-scale
current
range
is
the
Range Switch
setting
times
the Multi-
plier
Switch
setting.
When selecting
the Multiplier
Switch
setting,
remember
smell
settings
permit
lower
current
source
resistance,
and larger
settings
im-
prove
instrument
zero
stability.
Check
the caution
in
subparagraph
3a below.
3.
With
the
fast
method,
the
input
drop
is
reduced
and the
response
speed
is
increased
at
least
100 times,
However,
follow
these
cautions:
a)
The internal
impedance
of the unknown
current
source
should
not
be less
than
.l
of the value
of
the
feedback
resistor
being
used.
Otherwise,
the
full
feedback
voltage
cannot
be developed
at
the
input,
and zero
instability
results.
The feedback
resistor
value
is
the
reciprocal
of the AMPERES range
of
the
Range Switch.
b)
The low side
of the
OUTPUT Receptacle
is no longer
grounded.
Therefore,
do not
ground
recorders
or oscilloscopes
to the
Elecerometer's
case,
such as
through
the ground
lead
of the
power
cord.
Another
alternative
is using
the
unity-gain
output
(paragraph
Z-10).
C)
Do not
use the
fast
method
to measure
capacitor
leakages.
Connecting
a capacitor
to the
input
causes
the
circuit
to be transformed
into
a differ-
entiator,
resulting
in extreme
sensitivity
to very
smell
voltage
transients.
e.
Galvanometric
Method.
1.
Operate
the Model
610B as a picoarmneter
in
the
fast
method
of operation.
Use en accurate
reference
current
source
to buck
out
the unknown
current
source.
Connect
as shown in Figure
6.
2.
Set the METER Switch
to CENTER ZERO and use the higher
current
ranges.
Adjust
the buckout
current
to indicate
null
on the l&de1
610B.
Increase
the
Electrometer's
sensitivity
as needed.
When the Model
610B is
as close
to null
as possible,
the
known reference
current
source
equals
the unknown
source
f
?hn Mrvi!a1 6,"R
c-l,Yv-cxnr r!s,<rl,no
current
Source
>
FIC;URE b.
Measuring
Current
by the
Galvanometric
Nethod.
Use an *ccurs.te
reference
current
source
to buckout
the unknown
current
source,
I,.
The
Xodel
6LOB, on its
current
ranges,
serves
es a null
detector.
Use a uhf-tee
fitting
at the Xodel
6lOB input.
Connect
the
Electrometer
to the
two sources
with
coaxial
cable.
Select
cable
carefully
for
very
low currents
(see
para-
graph
Z-3).
12
1064R
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