Keithley 237

236/237/238
Output
HI
Source
I
Measure
V
Output
LO
A.
Resistor
Limited
236/237/238
Output
HI
Source
I
Measure
V
OutputLO
•
High
resistance
when
cold.
Low
resistance
when
hot.
Fast
thennal
recovery.
B.
Thermistor
Limited
Load
Load
Figure
2-63.
Limiting
Capacitive
Reaction
Current
236/237/238
Output HI
Source
I
Measure
V
OutputLO
A.
Resistor
Clamped
(AC
or
DC
Voltages)
236/237/238
Output HI
Source
I
Measure
V
Output LO
B.
Diode
Clamped
(DC
Voltages)
236/237/238
Output HI
Source
I
Measure
V
OutputLO
c.
zener
Clamped
(AC
Voltages)
236/237/238
Output HI
Source
I
Measure
V
Output LO
D.
Resistor-Capacitor
Clamped
(AC
Voltages)
Load
Load
Load
Load
Figure
2-64.
Limiting
Inductive
Reaction
Voltage
+
+
2.27
SINK OPERATION
SECTION2
Operation
The
Model236/237
/238
functions as a source
when
it
is
delivering
power
to a load.
During
normal
source
opera-
tion,
current
will
flow
out
of
OUTPUT
HI
when
pro-
grammed
for a positive
output
(see Figure 2-65A). The
positive
output
would
result
in
a positive
measurement
placing operation
in
quadrant
I (see Figure 2-66).
When
programmed
for a negative
output,
current
will flow into
OUTPUT
HI
(see Figure 2-65B). The negative
output
will
result
in
a negative
measurement
placing operation
in
quadrant
ill.
With
an
external source
or
an
energy
storage device (such
as
a battery, capacitor
or
inductor) connected
to
the
out-
put,
the
Model236
/237/238
could
operate
as
a sink. As a
sink,
it
will dissipate
power
rather
than
source power.
For
example, a
test
system
to check a
battery
may
require
that
it
be
charged
and
then
discharged.
The
Model
236/237/238
operates
as
a source
while
charging
the
bat-
tery.
When
programmed
to allow
the
battery
to dis-
charge,
the
Model236/237
/238
will
operate
as a sink.
Constant
I Load
The
Source
Measure
Unit
can
be
configured to function
as a constant
current
load.
The
example test system
in
Figure 2-67
shows
the
most
accurate
method
to
use
the
instrument
as a constant
current
load.
Assume
that
the
test requires
the
12V
battery
to
be
discharged
at
lmA.
To
accomplish this,
the
Model236
/237/238
is configured
to
Source I
Measure
V.
The
!soURCE
is
set
to
output
-lmA
and
V
coMPUANcE
is
set
to
20V. V
coMPUANCE
must
be
greater
than
12V
to
keep
the
Source
Measure
Unit
from going into
compliance.
Configured
in
this
manner,
the
Model
236/237/238
will
sink
a constant
lmA
from
the
discharg-
ing
battery. The Source
Measure
Unit
will
be
operating
as
a
sink
in
Quadrant
II (-I, +
V).
If
the
polarity
of
the
battery
and
!soURCE
were
reversed,
the
Model236
/237/238
would
operate
as
a
sink
in
Quadrant
IV (+I,
-V).
Another
way
to
use
the
Model236
/237/238
as a constant
current
load
is
shown
in
Figure 2-68.
The
Source Measure
Unit
is configured
to
Source
V
Measure
I.
With
V
soURCE
set
to
a
value
less
than
12V,
the
battery
will discharge
current
into
the
Source
Measure
Unit.
The
test
requires
that
the
battery
discharge
at
lmA.
With
V
soURCE
set
to
OV,
the
bat-
tery
could
discharge
much
more
current
than
lmA.
However,
with
current
compliance limit
set
to
lmA,
the
Model236
/237/238
will
go
into compliance
and
the
bat-
tery
will
discharge
at
a constant
lmA.
This
method
of
controlling
current
with
the
!CLAMP
is
not
as accurate as
the
previous
method
that
controls
current
with
the
!soURcE.
2-101