Triplet Oil Stress Relief
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Last update: June 6, 2013
- The camera-collimator lens can contains a triplet with a large
CaFl element in the center. Cargille 1160 oil is used to optically
couple the three elements of the triplet. Oil was chosen over an
optical glue such as Sylgard in order to allow flexibility later on,
should the triplet need to be dismantled for some reason. Cargille 1160
was found to be UV transmissive, and unreactive to Sylgard and the
rubber O-ring which seals the oil layers in the lens cells.
- At the top of the cells, a small pliable tube allows overflow
relief. The tube comes out of the top of the spectrograph, and is
connected to a small plastic bowl. We've stretched a finger cot
over the plastic bowl. The finger cot material is very flexible
compared to the seals in the lens cell or the other tubing. When
the atmospheric pressure changes, or the oil expands or contracts
because of changes in temperature, the finger cot gives before the
seals do. In general, the oil should not come anywhere near the
finger cot or the part of the tubing that sticks out of the
spectrograph.
- The finger cot should be checked before each run, and replaced if
it has been damaged.
- In addition, there is a spigot in the tube, near the finger
cot. At one point, we had to transfer MAESTRO into the telescope
chamber from the loading dock area by tipping it 90 degrees and pulling
it through the hatch. In order to prevent oil from the triplet
spilling into the tube and finger cot area, we put a spigot in the
line. The
labels on the spectrograph say that the spigot may be open when the
spectrograph is pulled through the hatch because the spectrograph was
always tipped the same way, with the finger cotalways above the
triplet.
- The spigot is accessible when the spectrograph is mounted on the
telescope.
- The spigot should be closed when the spectrograph is
on
the telescope and the telescope is tipped over, e.g. when the operator
is opening the mirror cover, or when you are observing. Since the
spectrograph rotates, the finger cot may not always be above the
triplet.
- The spigot should be open whenever the spectrograph is
experiencing a change in atmospheric pressure, or temperature.
Specifically, the spigot should be open when the spectrograph is being
transported up and down the mountain.
In sum:
Spigot open: During
transport, and whenever there is a change in pressure or temperature.
Spigot closed: When
observing, or tipping the spectrograph for any reason.
- The spigot is OPEN when its handle is parallel to the
tubing. The spigot is CLOSED when its handle is perpendicular to
the tubing.
- All the plumbing in this area was purchased at Ace Hardware, in
the lawn sprinkler section.
Pictures:
Photograph of the Triplet Oil Stress Relief system, with the
spectrograph on the cart.
View you see when the spectrograph is mounted on the telescope.
Spigot is located above the "OPEN CLOSED" label.
A bag of spare finger cots is kept in the Maestro cabinet in the
common building:
