- Disconnect external electronics and cap sockets.
- Put dewar in handling fixture.
- Ground dewar to good earth ground.
- Plug Lakeshore thermometer into grounded AC outlet.
- Plug temperature sensor cable into thermometer.
- Plug cable into T1 on level-shifter box on dewar.
- Turn on Lakeshore thermometer box.
- Read all temperatures. Dewar should not be opened until all
4 temperatures have been more than 2 deg. Celsius above the ambient
dew point for more than 12 hours. See Warming Dewar.
- Attach vacuum fitting with handle retracted to one of the
dewar vacuum ports.
- Attach pressure regulated gas cylinder of HP dry nitrogen
or argon to the vacuum fitting. The pressure should be regulated
to no more than 5 psi.
- Purge the line by loosing the valve connection.
- Slowly open the valve to a flow rate of no more than 0.5 l/s.
Keep positive pressure in the line.
- When the internal pressure in the dewar is enough to allow
gas to escape from the other vacuum port, close the vacuum fitting
valve, remove and cap.
- Set both filter wheels to zero by decreasing the numbers on
the counters.
- Set dewar upright so lid is up.
- Incrementally loosen cap screws on lid in crisscross-cross
fashion. Note that there is still a small amount of pressure in
the dewar which will escape when the lid is loosened
- Remove the 8 screws, the lid and the O-ring. Store in clean
dry, dust free place.
- Do not touch the inside of the lid or any unpainted surfaces
that must be low emissivity, such as the MLI. These can be cleaned
with isopropanol if touched.
- Incrementally loosen the captive cap screws on liquid nitrogen
shield lid. Pull up slightly on the spring loaded cups as you
go to free the lid.
- Remove the lid and put in a clean dry place. When all
screws are free the lid will come off easily.
Removing the Field Optics Assembly
- Loosen all 8 captive cap screws at the edge of the plate.
They are pointed by pencil lines on the baffle box top.
- Grab baffle box by hand, and making sure that all the screws
are free, lift it slowly keeping it horizontal. Do not force;
the fit is very close but the assembly can be jockeyed out without
any force.
- Put the assembly in a clean, dry, dust free place.
Removing the Filter Wheels
- Screw filter wheel handle into center of outer wheel until
just barely snug.
- Retract spring loaded idler wheel from edge of wheel by rotating
the appropriate one of the two handles at the edge of the wheel.
A detent will keep the wheel retracted at about 180 degrees rotation.
- Lift the wheel out using the center handle.
- Unscrew the handle and put the wheel in a clean dry dust free
place.
- The inner wheel is remove by the same procedure except that
the idler wheel for the outer wheel must also be retracted and
the fit is snug and the wheel must be jockey out. DO NOT FORCE.
- The lens is now exposed so install the temporary cover plate.
- Cover the dewar to protect it from dust. If it will be left
for more than an hour purge it with dry nitrogen or argon.
Installing the Filter Wheels
- Set both filter wheel shafts to zero on the counters by turn
to decreasing numbers
- Screw the handle into the center of the filter wheel that
will be the inner one.
- Remove all lids.
- Make sure both idler wheels are retracted and that their handles
in the detent position.
- Orient the inner wheel so that the zero position is toward
the fiducial line on the wall next to the lens.
- Jockey the wheel into position in the well.
- While keeping the fiducial line at zero on the wheel aligned
with the fiducial line on wall near the lens, engage the gear
teeth on the outside of the wheel with the teeth on the spur gear
near the lens.
- Now engage the fixed idler in the groove in the edge of the
wheel.
- While holding the engagement rotate the handle to engage the
spring loaded idler wheel in the groove.
- Check the alignment of the fiducial lines.
- Rotate the filter wheel by turning the motor shaft clockwise
to 10 on the counter.
- Rotate slowly counter clockwise to 0. Do not overshoot.
- Recheck the alignment of the fiducial lines.
- Realign if necessary. Note: If the alignment is off by a fraction
of a tooth the shaft can be align to zero by removing the cap
on the number counter shaft and loosening the two silver tipped
socket head set screws.
- Install the outer filter wheel in the same way.
- Installing the Field Optics Assembly
- Check the assembly for dust.
- Grasp the assembly by the baffle box.
- Orient it and lower it horizontally into the nitrogen shield.
The fit is close; DO NOT FORCE.
- Check that the two pins in filter wheel assembly plate are
engaging in the field optic assembly plate.
- Start all 8 captive socket head cap screws on the outer edge
of the plate pointed to by pencil lines on the top of the baffle
box. DO NOT TIGHTEN.
- Check the slit mechanism by rotating the SLTS and SLTM shafts
and see if the racks move.
- Tighten the screws bit by bit while checking the slit mechanism
until all the screws are tight. DO NOT OVER TIGHTEN.
- Pick up the radiation shield lid by two of the captive screw
cups on opposite sides of the lid.
- Align the lid loosely on the radiation shield and wiggle the
screw cups to engage all of the screws in the holes.
- Make sure no screws are sticking outside or inside of the
shield.
- Wiggle the lid until it seats on the radiation shield.
- Using a 5/64 hex driver start the threads of all of the screws
in holes.
- Tighten the screw in a crisscross-cross fashion a little at
a time until they are tight. DO NOT OVER TIGHTEN.
- Turn the dewar until the top is slight below horizontal and
the electronics boxes are up using the gear drive on the handling
fixture.
- Check that the O-ring sealing surface on the dewar jacket
is undamaged and clean.
- Check that the O-ring grove in the lid is undamaged and clean.
- Check that the lid O-ring is clean and coated with a very
thin coating of vacuum grease.
- Put the O-ring in the grove.
- Clean the inside of the lid of any grease the might have gotten
on its surface. Watch out for lint or dirt on the O-ring when
you do this.
- Align the lid over on the vacuum jacket and start the two
top screws keeping the O-ring in its grove.
- Start the other six screws.
- Rotate the dewar so that the lid is up.
- Align the lid on the vacuum jacket by hand.
- Tighten all 8 screws in a crisscross-cross fashion until tight.
- Check that the is no gap under the lid.
- Go around and tighten all the lid screws again so they do
not loosen when vacuum is applied.
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