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: http://www.naic.edu/~phil/optics/tdposaug01/tdposforprf.html
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Tiedown positions to correct for pitch, roll, focus errors.
aug,2001
The pitch, roll, and focus errors of the telescope
(measured and computed in AO9
survey and tilt
sensor pitch,roll) can be corrected by using the tiedowns. The plots
below show these motions over the entire range of azimuth and zenith angle.
They were computed using the following parameters:
aug01 theodolite and tilt sensor data corrected to the reflector of curvature
using a radius of 869.8171 feet.
A tiedown reference position of 14.697,14.438,13.065 (td12,td4,td8)
The reference position should be in focus at 72 degrees F.
All of the plots are for 72 degrees F. Larger
Td positions means that the jacks are pulling down farther (the platform
is lower). Td position of zero has the jacks fully extended. Errors are
the current values. Corrections are what you need to do remove the error.
These plots do not include the tension in the cable. When the dome at high
za passes in from of a tiedown cable, the cable may go slack (even though
the tiedowns are not fully extended). As soon as a tiedown goes slack,
the corrections no longer work.
Tiedown positions to correct the pitch,roll, focus errors
versus azimuth for za 2 through 20 degrees. The color code is :Black td12,
Red td4, Green td8. The tiedown limits are over plotted. This is all for
72 Degrees F. Increasing the temperature would cause the curves to move
down at .2 inches /degF above 72 F.
This shows the motion of the tiedowns relative to the
reference position. Zenith angles 1-20 degrees have been over plotted (the
dotted line is za=20). The tiedown limits have also been included. Anything
outside the horizontal lines is beyond the reach of the tiedowns. This
plot does not include the tension in the tiedowns. Including the tension
would decrease the allowable range since without tension, you cannot
control a corner.
The pitch, roll, and focus errors are plotted versus
azimuth for za 1 to 20 degrees (the color changes every two degrees)
-
Fig 1. The pitch error is on the top and the roll error is on the bottom.
-
Fig 2. Top: the pitch and roll errors are added in quadrature. Bottom:
the radial focus error in inches. Positive numbers mean the platform is
too far from the dish.
-
Fig 3. Top: the focus error projected to tiedown inches (cos(za)*1.74 tdInches/platforminch).
Bottom: You correct for the pitch by tilting the platform along the azimuth
arm. This introduces a focus error. The bottom plot is the size of this
error in tiedown inches (- means the platform is too low).
The pitch, roll, and focus errors are plotted versus
zenith angle for azimuths =0..360 in steps of 10 degrees.
-
Fig 1. The pitch and roll errors versus za.
-
Fig 2. Top: the radial focus error in inches. Bottom: the radial
focus error projected to tiedown inches.
-
Fig 3. The focus error in tiedown inches caused by the pitch correction.
-
Fig 1 Top: how far you need to move the tiedowns to correct for a given
pitch error (it does not include the focus correction). Bottom: The tiedown
error caused by correcting the pitch for za 1->20.
processing: idl/td/meeting.plt
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