Keithley 616 Instruction Manual page 12

OP ERATING INSTRUCTIONS
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SOURCE
3-7.
HOW TO M EASURE CURRENT.
used to measure currents from ±IO- I S ampere to 200
mill iamperes . Although the Model 616 is useable as
a
general purpose p icoamme ter, it has certain charac­
teristics which enab le reliab le measurements of very
small currents with fast respons e .
a . Normal Mode Current Measurements .
mode for current below 1 0 - � A . )
Model 616 measures current over a wide range.
the FAST/NORMAL switch is set to NORMAL , the Model
616 operates 8S a shunt-type p icoammeter in which a
resistor is connected d irectly acrOSB the input ter­
minals. The Model 616 measures the voltage drop
across the shunt resistors where V 1N
This method of measurement is typical of ' m ost multi­
meter current measuring techniques .
616 as a shunt-type picoammeter, set the front panel
controls as follows:
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1 0
RANGE
SENSITIVITY AUTO
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AST /NORMAL
NORMAL
NOTE
is
range
Full determined by the
sens itivity setting and the AMPERE
range s e t t ing .
Connect a Model 6 011 Tr iax Cable (or other sh ielded
tr iaxial cable) to the INPUT receptacle.
length as short as possible to reduce the slowing
effects of cable capacitance.
need occasional adjus tment to reduce any voltage
offset which may occur due to temperature var iat ion s .
To rezero the Model 616 , set the ZERO CHECK switch
to CHECK posit ion and adjust the front panel zero
control for a 0- 0-0- 0 d isplay.
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MEASURING
POINTS
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FIGURE 7 .
Operation As An Amm e ter in NORMAL
The Model 616 can be
(Use FAST
In this mode, the
X
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R S '
IN
a
To use the Model
AMPERE (or appropriate range)
Keep cable
The zero control may
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The Model 616 may exhib it a large amount of
zero offset or drift immediately after an
overload or a long period of storage.
addition, the offset current may exceed the
specificat ion for a short time until the
Model 616 is sufficiently s tabilized .
though the offset current of the Model 616
is well below offset found in conventional
voltmeters , the effects of the offset current
When
charging the inpu t capac itance may be noticed
when the input is open.
switch to d ischarge the offset charge .
Do not use the 1 0 volt and 100 volt sensi­
t ivity settings for RANGE switch s e t t ings
of 1 0 - 1 , 1 0 -2 , 1 0 - 3 , and 1 0 -
the voltage exceeds 2 volts o n these ranges ,
overheating of the resistors could result
w ith subsequent degradat ion of accuracy in
the AMPERE mode.
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FIGURE 8.
F1RST STAGE Xl OUTPUT
AMPLIFIER
RANGE
RESISTOR
ELECTROMETER
v =
I x R IN
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Mode .
NOTE
Use the ZERO CHECK
CAUTION
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Measuring
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IJb &fror in readlns due to circuit loadlns '" -100
R + R in
If R in« R, I � I meter and IJb error � 0
R
Loading Effects in Amm e ter Function.
MODEL 616
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4
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AMMETER
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