Platform corner height vs dome za
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:
show how the platform corners deflect as the dome moves in azimuth
and zenith angle.
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 previous shimming (feb03) moved 1 inch at za=20 to correct a .125 pitch
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
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.
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).
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.
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)
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.