2.17 SUPPRESS
JTIME SUPPRESS
De
••
FILTER
AUTORANGE
De De
MEASURE
Suppression allows a stored offset value to
be
subtracted
from subsequent measured readings.
When
SUPPRESS
is enabled, the next conversion taken
in
OPERATE will
be
internally stored as a baseline. All subsequent read-
ings will
be
the
difference between
the
suppressed value
and
the
actual signal level. The suppressed readings can
be
as small as
the
measurement resolution
of
the
Source
Measure
Unit
or
as large as full range.
The baseline value maintains its value regardless
of
range. For example, if a
0.5V
measured reading is
sup-
pressed
on
the
1.1Vor
1.5V (Model238) range,
it
will re-
main
at
0.5V
on
the
llV,
15V
(Model 238),
llOV,
and
1100V
(Model237) ranges.
A suppressed value is
not
saved for
both
the
voltage
source
and
the current source. The respective baselines
will
be
lost
when
the sources are toggled.
Using
suppression shifts the dynamic
range
of
the
meas-
urement.
At
4-digit resolution,
up
to
±11,000
counts (for
volts) can
be
processed
by
the
A/D
and
displayed.
When
a measurement is suppressed, the display treats
that
value as a zero,
but
the
A/D
converter does not. For ex-
ample, if
+4V
is suppressed
on
the
11
V
range
of
236/237,
thedisplaywillreadOV,
buttheA/Dconverterwill"see"
+4V (4,000
counts). With
+07.000 V
displayed,
the
A/D
converter is actually processing
+llV
(11,000
counts)
which is
the
maximum. Thus,
the
dynamic measurement
range has been shifted to a range
of
-15V to +7V.
Suppressing a value while
in
de operation will process
readings already stored
in
the
sweep
buffer. The
sup-
pressed value will
be
algebraically subtracted from every
measurement
point
in
the sweep. For example, assume
the
sweep
buffer contains
the
following
measured
read-
ings; 1mA, 2mA, 3mA
and
4mA. Suppressing
O.SmA
while
in
de operation will change
the
sweep
buffer read-
ings to
O.SmA,
1.5mA, 2.5mA
and
3.5mA.
This
allows
you
to
run
a
sweep
and
then
afterwards
use
suppression to
+
+
SECTION2
Operation
cancel
an
offset.
When
SUPPRESS
is later disabled, the
readings
in
the
sweep
buffer will
return
to
the
measured
values (1mA, 2mA,
3mA
and
4mA).
The first measurement point
of
a sweep can
be
sup-
pressed. Prior to starting
the
sweep, enabling SUPPRESS
will cause its light to
start
blinking, indicating
that
it
is
waiting for a trigger to start
the
sweep.
When
the
sweep
is started,
the
first measurement point is suppressed,
and
subsequent
measured
points reflect
the
suppressed
value.
If
SUPPRESS
is disabled after
the
sweep is com-
pleted,
the
readings
in
the
sweep
buffer will
return
to the
originally
measured
values.
WARNING
Voltage
on
the
output
may
be
larger
than
the
displayed
measured
value. For example,
if
a
75V
baseline
is
stored, a voltage
of
+
lOOV
will
result
in
a
displayed
measured
value
of
only+25V.
To
use
suppression, perform the following steps:
1.
Cancel
SUPPRESS
if currently enabled.
2.
For de operation:
A.
Configure
the
unit
so
that
it
will
output
a signal
and
display
the
measurement to
be
suppressed.
B.
Press
SUPPRESS. The displayed measurement
will zero
and
all subsequent measurements will
reflect
the
suppressed value.
3. For
sweep
operation:
A.
Configure the
unit
for a
sweep
as explained
in
paragraph2.19.
B.
Press
SUPPRESS.
After
the
sweep
is triggered to
start,
the
first measurement will
be
suppressed.
All subsequent measurements
in
the sweep will
reflect
the
suppressed value.
NOTES
1.
Factory initialization disables
SUPPRESS
for
both
sources.
2.
When
SUPPRESS
is enabled, the first measurement
will
be
used
as
the
suppression value. The
SUP-
PRESS
indicator light will blink until
that
measure-
mentis
made.
Be
careful
not
to inadvertently change
the
source level before
the
first measurement is
made.
IEEE-488 Bus
Operation
The
Z
command
is
used
to control suppression.
2-53
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