Keithley 237

SECTION1
Getting
Started
lsoURCE
-
The Models 236
and
237
can source from
±lOOfA
to
±lOOmA.
The Model 238
has
an
additional
source range
of
±lA.
The programmable voltage compli-
ance is
up
to
110V
for the Model
236, 1100V
for the 237
(except
110V
on
the
lOOmA
source range),
and
110V
for
the
Model
238
(except
lSV
on
the
lA
source range).
Compliance limits are
used
to protect external
circuitry
or
OUT (devices
under
test). Setting
an
appropriate cur-
rent compliance (!-limit) can
prevent
excessive
power
dissipation
in
a device. Setting
an
appropriate voltage
compliance (V-limit) can protect a device susceptible to
damage
by
overvoltage. The Source Measure
Unit will
never exceed
the
user
programmed
compliance limit.
Source
Only-
To
use
the
Source Measure
Unit
only as a
source, simply ignore measure readback (displayed
measurements for
de
operation,
and
measure values
in
the sweep buffer for
sweep
operation). For IEEE-488
bus
operation, measure readback can
be
disabled (G com-
mand).
Measure Capabilities
IMETER
-
The Model 236 can measure from
±lOfA
to
±lOOmA,
the
Model
237
from
±lOfA to
±lOOmA
(except
lOrnA
on
the
1100V
source range),
and
the
Model238
from
±lOfA
to
±lA
(except
lOOmA
on
the
110V source
range).
VMETER-
The
Model236
can measure from
±10J.1V
to
±110V,theModel237from±10j.1Vto±1100V(except110V
on
the
lOOmA
source range),
and
the
Model238
from
±lO!!V
to
±110V
(except
lSV
on
the
lA
source range).
The selected compliance range is also the
maximum
measurement range. For example,
if
compliance is pro-
grammed
to
SOmA
(100mA
range), measurements
(up
to
SOmA)
will
be
made
on
the
lOOmA
range. However,
if
AUTORANGE is enabled, the Source Measure Unit
will
always
go
to
the
lowest (most sensitive) possible range to
make the measurement.
Measure
Only-
The Source Measure
Unit
can
be
used
as a stand-alone voltmeter
or
current
meter
(see
Figure 1-2). To measure voltage, select
Source
I Measure
V
and
set the current source to zero
on
the
lnA
range
(0.0000
nA). To measure current, select Source V
Measure
1-4
+
+
I
and
set
the
voltage source to zero
on
the 1 V
range
(O.OOOOV).
Source-Delay-Measure
Source
Measure Unit
operation (de
and
sweep) consists
of
a series
of
source-delay-measure
(SDM)
cycles (see
Figure 1-3). During each
SDM
cycle,
the
following oc-
curs:
1.
Set
the
source
output
level.
2.
Perform
the
delay.
3. Make
the
measurement.
The delay is
used
to allow the source to settle before the
measurement is made. The total time period of
the
delay
includes
an
internal (default) delay
and
the
user
pro-
grammed
delay.
With
the
default delay enabled, a short delay is
used
to
allow for internal settling
on
the
low
current ranges. The
default delay is approximately equivalent to five RC time
constants of
the
selected current range for either Source I
orSourceV.
A programmable delay (from
Omsec
to 65sec) is available
to compensate for longer settling caused
by
external
cir-
cuitry.
The
more
capacitance seen
at
the
output,
the
more
settling time
that
is required for
the
source. The actual de-
lay period
needed
can
be
calculated
or
determined
by
trial
and
error. For resistive loads
and
higher currents,
the
programmable delay can be set to
Omsec.
Operating
Functions (DC
and
Sweep)
In
de
operation (de function selected), a constant de volt-
age
or
current is applied to the output. This operation
consists
of
a continuous series
of
SDM
cycles. During
each
SDM
cycle, the
measured
reading will
be
internally
updated,
making
them
available for display. The
pro-
grammed
source value is displayed
on
the
left side of the
display
and
the
subsequent measurement is
shown
on
the
right side. All readings are
not
displayed. The display
is slower
than
the internal measure
update
rate, however
it
is possible to get all readings over
the
bus.
In
sweep
operation (sweep function selected),
the
Source
Measure Unit
sweeps
through
a user-defined list
of
points specifying source values
and
delay times for a
waveform (fixed level, staircase
or
pulse).
An
SDM
cycle