Keithley 610C, Instruction Manual

Page: 15 / 44

Fast Current Measurements. When the FEEDBACK
switch is set to FAST the current is determined by
the voltage developed across the RANGE resistor in
feedback loop. This method is useable for current
levels from
10-5
to 10-14 amperes. Typical rise times
for the 6l0C when used in the FAST mode are given in
Table 6.
1.
Set the controls as follows:
ZERO CHECK
RANGE Switch
MULTIPLIER Switch
FEEDBACK Switch
METER Switch
LOCK
10-6 AMPERES
1
FAST
CENTER. ZERO
2. Connect the 6l0e input terminals in series
with the current to be measured. Unlock the ZERO CHECK
Switch to make a reading. Increase the sensitivity
using the RANGE switch. The full scale current is
determined by multiplying the RANGE setting times the
MULTIPLIER setting. Use the smal�est Multiplier set­
ting to obtain the best accuracy. Example: A Multi­
plier setting of 0.1 means that the meter will read
0.1
Volts
maximum.
3. When using the OUTPUT the recorder cannot be
referenced to case ground since the low side of the
output is floating.
c. Galvanometric Current Measurements. In this
method the 6l0C is used as a null detector. The
610C should be used in conjunction with an accurate
current source such as the Keithley Model 261 as
shown in Figure
7.'
2-5. RESISTANCE MEASUREMENTS.
the FEED-
is deter-
mined by measuring voltage drop across the unknown
resistance shunting the input. The 6l0e injects a
constant current at the input terminals. The voltage
drop is therefore proportional to resistance.
b. Ohms Guard Resistance Measurements. The 610C
can also be used in the FAST mode when the unknown
resistance is connected between INPUT high and GUARD
on the rear panel of the instrument. This method is
recommended for measurements from lOll to 1014 ohms.
c. Resistance Measurements. This
method is useful when the drop across the
unknown resistance must be accurately controlled.
For this measurement the 6l0C is used in the NORMAL
mode with the RANGE switch set to AMPERES. The
To deter­
should be
The
circuit connections are shown in Figure
8.
mine the resistance the Multiplier setting
subtracted from the voltage source setting.
resistance is therefore the ratio of the net
divided by the current measured by the 610C.
voltage
NOTE
If the voltage applied to the sample is not 100
times the Electrometer input drop, then the un­
known resistance is calculated as follows:
lMeasured
where Rx
=
Unknown resistance,
VSource
=
Applied voltage,
Eq. 1
VInput Drop
=
Electrometer input voltage
drop
and lMeasured
=
Current measured by Electrom­
eter.
2-6. CHARGE MEASUREMENTS.
a. Current Charge or current inte­
gration measurements can be accomplished using the
610C in the coulombmeter mode. The electrometer indi­
cates the voltage developed across a capacitor con­
nected between the input and feedback point. The
voltage indicated is proportional to the
of
the applied current.
1. Set the controls as follows:
ZERO CHRCK Switch
RANGE Switch
Multiplier Switch
FEEDBACK Switch
LOCK
10 -
7
COULOMBS
1
FAST
2. Connect the 6l0C input terminals in series
with the current to be measured. Unlock the ZERO
CHECK switch to make a reading. Increase the sen­
sitivity using the RANGE SWitch. The coulombmeter
reading is determined by multiplying the meter
reading times the RANGE switch COULOMBS setting.
NOTE
The input offset current of the electrometer
contributes a charge of 5 x 10-15 coulomb per
second and should be subtracted from the actual
reading.
3. After each coulombmeter reading is made, dis­
charge the integrating capacitor in the electrometer
by locking the ZERO CHECK switch for at least 20
seconds before making another measurement.
NOTE
For a more complete discussion of current
integration, request the Keithley Product
Note entitled "Using the Electrometer Volt­
meter as a Current Integrating or Charge
Measuring Instrument."
CAUTION
The Model 6l0C ohms circuit has a compliance voltage
to 125 volts. This means that up to 125 volts will
be present at input HI and near panel Xl if the ZERO
CHECK switch is OFF and input HI and LO is open-cir­
cuited. Always set ZERO CHECK to ON before connect­
ing or disconnecting to the input when using the
OHMS function.
7