Keithley 237 - SECTION 4 Principles of Operation; 4.5 POWER SUPPLY

SECTION2
Operation
8=
lOrnA
9=
lOOmA
10=
lA
(238)
*illegal V -source
option
*
*
*
HP
BASIC
4.0
Programming Example:
OUTPUT
716;
"Fl,OX"
OUTPUT
716;
"L5,2X"
Select Source
I
Measure
V
(de operation)
Set
compliance to
SV
and
select
11
V
or
15V
meas-
urement
range.
Complete information concerning the IEEE-488
bus
and
this
command can
be
found
in
Section
3
IEEE-488
Refer-
ence.
2.13
AUTORANGE
With AUTORANGE enabled, the
Source
Measure Unit
will
go
to
the lowest possible (most sensitive) range to
make the measurement. For example,
with
a
3V
compli-
ance limit
11
V
or
15V
(Model 238) range,
O.SV
will
be
measured
on
the
1.1
V
or
l.SV (Model
238)
range
if
autorange is enabled.
With a pulse sweep saved
in
the sweep buffer,
themes-
sage
"PULSE
TIME
NOT
MET"
will
be
displayed
when-
ever AUTORANGE is enabled. This message indicates
that the programmed
on
and
off times of the pulse will
most likely
not
be
met
when
a measurement range
change occurs.
H unspecified pulses cannot
be
tolerated
in
a test,
use
a fixed measurement range to avoid range
changes.
The AUTORANGE
button
toggles between autorange
and
the fixed range selected
when
compliance
was
set.
When AUTORANGE is enabled, its indicator light
will
be
on.
Autorange
Thresholds-
When a measured reading is
increasing,
an
autorange to the next highest range
will
oc-
2-48
+
+
cur
when
full
scale is surpassed. (As described
in
para-
graph
3.7.2, the instrument actually upranges to the com-
pliance range, then downranges to the required measure
range.) For example, assume a measured reading of
+0.8971mA
(lmA
range). The Model 236/237/238
will
autorange
up
to the
lOrnA
range
when
the reading sur-
passes
+l.OOOOmA.
When
a measured reading is decreasing, autorange to the
next lower range
will
occur
when
9%
of
full
scale
is
reached. For example, assume a reading of
+Ol.OOOmA
(lOrnA
range). The Model236
/237/238
will
autorange to
the
lmA
range
when
the reading decreases
past
+00.900mA. For voltage ranges, downranging
will
occur
at
8.1%
of
full
scale,
with
the exception of the
l.SV
and
15V ranges
of
the Model238,
where
downranging occurs
at
9%
of
full
scale.
NOTES:
1.
When
upranging
or
if
a measurement range change
occurs while the
unit
is
in
compliance (COMPLI-
ANCE
indicator blinking or
when
upranging), the
Source Measure Unit
will
momentarily
output
OV
or
OmA.
2.
Autorange should
not
be
used
when
optimum
speed
is required. The effects of autorange
on
sweep per-
formance is covered
in
paragraph
3.7.3.
IEEE-488 Bus
Operation
Over
the bus, the compliance limit
and
measurement
range (including autorange) are set using the L command
(see the previous paragraph).
Note
that
autorange can
be
controlled
by
sending only
the range option
with
the L command. The compliance
option
need
not
be
sent. The format for sending only the
range option
is
as follows:
L,(range)
As defined
in
paragraph
2.12, range option
0
selects
autorange. Thus, sending
L,OX
over the
bus
will enable
AUTORANGE. Sending
any
other valid range option
(one
through
ten)
will
disable AUTORANGE. A valid
fixed measurement range is equal to
or
higher
than
the
compliance limit.