Brewer Ozone Spectrophotometer Pointing and Levelling C.T. McElroy York University Canada.
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Transcript of Brewer Ozone Spectrophotometer Pointing and Levelling C.T. McElroy York University Canada.
Brewer Ozone SpectrophotometerPointing and Levelling
C.T. McElroyYork University Canada
September, 12-16, 2011
Brewer Workshop Beijing, China
2
Underlying Principles• Careful, detailed optical design
• Optical and mechanical mounts are kinematic
• Loads are carried in tension or compression– Not bending
• Clear understanding of system integration
• Temperature compensation when needed“Other instruments are climate controlled and still don’t have goodwavelength stability. The Brewer operates at a wide range of ambienttemperatures and has good wavelength stability. Why is that?” – Brian Gardiner
September, 12-16, 2011
Brewer Workshop Beijing, China
3
Kinematic Design
• A solid body has 6 degrees of freedom
• 3 translation degrees
• 3 rotation
• Proper design constrains, but does not over constrain these degrees of freedom
• Over-constraint causes stress and leads to temperature-induced instability and failure
September, 12-16, 2011
Brewer Workshop Beijing, China
4
Goals: Pointing and Tracking
• The Brewer uses an altitude/azimuth mount
• Axes must be perpendicular to each other
• Azimuth rotation axis must be vertical
• The procedure uses levels and gravity
• The azimuth axis is made vertical
• Then the elevation axis is made horizontal
• Therefore they will be perpendicular
September, 12-16, 2011
Brewer Workshop Beijing, China
5
Tracker Screws
Three instrument levelling screws
Degrees of Freedom
xy
z
>
>
3 translation0 rotation
2 rotation
1 rotation
3 translation
3 rotation
September, 12-16, 2011
Brewer Workshop Beijing, China
7
BrewerExample
DiffractionGrating
3 Aluminum Blocks
Plane
Hole
SlotSprings load all three
September, 12-16, 2011
Brewer Workshop Beijing, China
8
TrackerAzimuthRotationalAxis Must BeVertical
Elevation Axis Must be PerpendicularTo the Azimuth Axis
3 Feet == Kinematic Connection to Earth
Internal Screws in Tracker Base areUsed to Make the Axes Normal UsingLiquid Reflection
Software CorrectionFrom MechanicalZero to EarthCoordinates
Pointing AccuracyRequired ~0.1o
September, 12-16, 2011
Brewer Workshop Beijing, China
9
LevellingYou may find it easiest to levelthe tracker first – then add the Brewer and checkthe level again.
September, 12-16, 2011
Brewer Workshop Beijing, China
10
When is it Right?• With the bubble in the level showing ‘level’-
• Rotate the instrument through +/-180 degrees
• The instrument should be level at all angles
• If not:– Level on along a line between a pair of feet first– Adjust level to show level– Rotate 180 degrees– Adjust level half way, adjust leg(s) the rest of the
way - iterate back and forth until stable– Do the perpendicular axis
September, 12-16, 2011
Brewer Workshop Beijing, China
11
Levellingone Axis
< >
Top of case m ay not be para lle l to optica l axis
O ptica l axis
Use screw to centre bubble
Rotate Brewer 180 degrees:
Re-centre with screw – count turns
Back off half the number of turns
Level with tripod levelling screws.Rotate Brewer back 180 degrees.
An iterative procedure…
September, 12-16, 2011
Brewer Workshop Beijing, China
12
Orthogonalization - 1
• Set zenith prism to look upward
• Use a circular bubble level
• Place bubble level on prism surface
• Rotate prism to centre bubble laterally
• Adjust centre levelling screw inside tracker to level longitudinal axis
September, 12-16, 2011
Brewer Workshop Beijing, China
13
Orthogonalization - 2• If there are persistent sighting problems or in the
case of a new instrument– It may be necessary to check that the foreoptics rotation
axis is perpendicular to the azimuth tracker axis
• Assume that the prism surface is parallel to the foreoptics rotation axis (one face is on the bearing)
• Reflect a laser vertically downward onto the prism (use reflection from a liquid surface to set the laser)
• Adjust the centre screw in the tracker to make the reflection from the prism travel vertically upward
Brewer Practical
• Assembly and Disassembly• Levelling and Orthogonalization• Removing and Replacing the Covers• Changing Desiccant• Inspection of optics – Mirror, Grating, Lens• Servicing the Tracker• Resetting the Tracker Limit Switch• Various Tests and the Interpretation of the Results RS AP SH FR DT GS SL HG HP• Sunscan Results (SC)• Cleaning – and NOT Cleaning
Hands-on Activities
September, 12-16, 2011
Brewer Workshop Beijing, China
15
Now try it yourself….