4.
To exit from the menu, again press the MENU but-
ton.
NOTE
Changing the ac line frequency with a front
panel menu selection also changes the inte-
gration time
if
LINECYCLE
PERIOD
is pres-
ently selected. for example, a line frequency
change from
60Hz
to
50Hz also changes the
integration time from 16.667msec to 20msec.
2.2.7
Warm
Up
Period
The Source Measure
Unit
can be used immediately
when
it
is
first turned on. However, the unit
must
be allowed to
warm
up
for one hour to achieve rated accuracy.
2.2.8
Fan
Filter Cleaning
The Model236/237 /238 has an internal cooling fan to
vent heat out of the instrument case. The fan has a filter to
keep
dirt
and
dust
from entering the instrument case.
Contamination
on
pc board could result in degraded per-
+
+
SECTION2
Operation
formance. The fan filter
must
be cleaned periodically to
maintain internal cleanliness
and
proper ventilization.
Perform the following steps to remove
and
clean the fan
filter element:
1.
Turn off the Model236 /237/238. The fan
must
be off
in
order to prevent dirt
and
dust
from being ingested
into the instrument case while removing the filter
element.
2.
Position the instrument such that
you
are facing the
rear panel. The cooling fan is internally mounted to
the right-hand
end
of the rear
panel
The filter as-
sembly
is
mounted to the rear panel
in
front of the
fan intake vents.
3.
Remove the two screws that secure the vented
shroud of the filter assembly to the rear
panel
The
filter assembly
will
swing away from the rear panel
allowing the filter element to be removed.
4.
To clean the filter element, blow
out
the
dust
and
dirt
with pressurized
air
or
nitrogen.
5.
Reinstall the filter assembly onto the rear panel. The
two hinges
of
the filter shroud fit into the rear panel
vents. Make sure the filter element covers all the rear
panel intake vents.
2-5
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