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OPERATING INSTRUCTIONS
MODEL
616
FIGURi: 12
.
Null Method
lor Curreii
t
Me as
ureinent
3
-n
.
REC
O
RDER OUTPUTS.
The
Model 616 provides
several outputs
for
monitoring
an
analog signal.
±.
XI Ou
t
put (Unity Gain).
This
output can be
used
for
monitoring
the
input signal in applications
requiring
a
buffer amplifier.
1.
NORMAL
MODE.
In the
NORMAL MODE,
the
signal
at the
XI OUTPUT
(with
respect
to
LO) is
equal
to
the
input within
20
ppm
at dc.
The XI
OUTPUT
can
deliver
up to
1
inilliampere for
outputs up
to
200
volts
,
2.
FAST
MODE.
In the FAST MODE, the XI
OUTPUT
terminal
is
connected
to
input
LO.
For
unity gain
applications when
in FAST
mode
the
GUARD terminja
should
be used.
Typical rise times for various
current
ranges
is
shown in Table
3-6.
This data
is
representative
of
instrument response for unity
gain operation.
c.
GUARD OUTPUT.
This output can be used
with
the XI output for
recording purposes
or
special
measuring techniques such
as
guarded resistance
measurements.
1.
NORMAL
MODE.
In this
mode, the GUARD
terminal
is
connected
to the LO terminal.
2.
FAST MODE.
In
this mode, the GUARD
terminal
can
be
used
to
monitor
the
input current
when
the
Model
616
is
used
as a
FAST mode
picoarnmeter.
The
output
of the
GUARD terminal
is
proportional
to
the
Input current
where Vq
='
linput
^
^range*
The
GUARD terminal
is
also useful for making guarded
resistance measurements.
For this type
of
measure-
ment, the
unknown resistance
is
connected
between
input
HI
and GUARD.
The voltage developed
at
the
GUARD terminal
is
proportional
to the
unknown re-
sistance,
where
x
R^.
TABLE
3-6.
Response
at
GUARD
(Unity Gain) OUTPUT for
Fast
Current*.
b.
1
VOLT
OUTPUT.
This output
provides
a
1
volt
analog output
at up
to.
1
milliampere corresponding
Range
Setting
Rise
].
V
Time
10-907,
10
V
100
V
to a
full scale
input.
1
X 10-5
A
50 pS
100
pS
500
yS
1
X 10
^
A
1
X 10
^
A
300
pS
500
yS
1
mS
1.
NORMAL
MODE.
In the
NORMAL mode, the out-
2
mS
3
mS
5
mS
put polarity
is
opposite
the
input polarity.
1
X 10
A
10
mS
12 mS
15
mS
1
X
10
^
A
1
X
10":^;
A
1
X
10'
A
60 mS
60 mS
60 mS
2.
FAST MODE.
In the
FAST MODE,
the
output
300
raS
300 mS
300 mS
polarity
is the
same
as
Input.
3
S
3
S
3
S
*Typlcal instrument performance
(may
vary
from unit
to unit)
Tin'¥rtiTTr~r]iriiiiiii>iifiitiitiiri
iiimn
i
FIGURE
14.
Unity-Gain
(XI)
Measurement
.
12
0773
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