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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.

    Absolute tiedown positions for corrections versus Az for za 2->20 degrees.

        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.

    Relative tiedown positions for corrections versus Az for za 1->20 degrees.

        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.

    Pitch,roll, focus errors versus Az for za 1->20 degrees.

        The pitch, roll, and focus errors are plotted versus azimuth for za 1 to 20 degrees (the color changes every two degrees)
    1. Fig 1. The pitch error is on the top and the roll error is on the bottom.
    2. 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.
    3. 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).

    Pitch,roll, focus errors versus Za for az 0->360.

        The pitch, roll, and focus errors are plotted versus zenith angle for azimuths =0..360 in steps of 10 degrees.
      1. Fig 1.  The pitch and roll errors versus za.
      2. Fig 2.  Top: the radial focus error in inches. Bottom: the radial focus error projected to tiedown inches.
      3. Fig 3. The focus error in tiedown inches caused by the pitch correction.

    Tiedown motion versus pitch angle, and pitch focus correction.

    1. 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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