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Platform corner height vs dome za

dec03

The vertical motion of the platform corners was measured using the distomat data taken sep03 through dec03. For the ALFA installation we wanted to know if the 2 kips of ALFA would cause an appreciable pitch/focus error in the telescope alignment. If this was true, then we would have to reshim the elevation rails.
Data points from sep03 through dec03 that met the following criteria were used:

The carriage house was within .01 degrees of stow (za=8.835 deg).
The platform was within 1.2 inches of the reference height (1256.22 feet).

The plots show how the platform corners deflect as the dome moves in azimuth and zenith angle.

Fig 1. The plots shows the corner Height minus the average height versus azimuth angle for the data set. The 3 plots are corners: 12, 4, and 8. The spread in height at a particular azimuth is caused by the dome moving in zenith angle. The green lines are 90 degrees from where the azimuth points at a corner. Moving the dome at these za's should have no effect on the height of that corner (the platform is rotating about the corner direction).
Fig 2. The maximum corner motion occurs when the azimuth points at or opposite a tower. These plots used data within 1 azimuth degree of the corner directions. The black * are pointing at the tower, the red * are pointing away from the tower. For each tower, the plots cross at about 8 degrees za. Linear fits were done to each data set (green lines). The fits were then forced to be 0 at za of 8 degrees. The average fit gives the corner height-avgHeight vs za when the dome points at a tower (hght(In)=3.71452 - .464315*zaDeg). The constant part of the fit is set by the counterweight and the ch being at stow. The slope (.46 inches/zadeg) is a function of the dome weight and the az pointing at the tower).
Fig 3. The corner motion is caused by the weight imbalance of the two sides of the azimuth arm causing a torque. The top plot is a fit to the corner deflection versus the torque (when looking at a tower,ch at stow). The values used for the computation (distances, weights) are shown on the plot. The bottom figure has the added motion of a corner if you added 2 kips (2000 lbs ALFA weight) to the dome. At 20 degrees za there will be an added motion of .1 inches.

The previous shimming (feb03) moved 1 inch at za=20 to correct a .125 pitch error.

The results:

There is a +/- 5.3 inch vertical motion when the dome is at 19.5 deg and the az is aligned with/away from a tower.
There will be an extra +/- .1 inch motion caused by ALFA at these az,za.
The +/- .1 inch will add a pitch error of .125*.1= .013 degrees.

ALFA will not have a large affect on the pitch or focus caused by the platform tilt. This does not account for any added motion caused by the deflection of the elevation arm (it will probaby be much smaller).

FITS:

corner hght vs za (aligned with tower:): hght(In)=3.71452 - .464315*zaDeg
corner hght vs torque (lookin at tower): hght(In) = .89132 - .0003249*Torque(kip-ft)

NOTES:
I hope that J. vellozzi does not revert to his previous unbalanced limit of 11500 kip-ft. We currently have 19000 kip-fit imbalance with the dome at 19.5 degrees za.

processing: x101/lr//cornertilt_dec03.pro

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