Adjustertests March 2003

Since November 2002 the rms of the dish is 20 to 25 micron (depending on the definition used to calculate the rms). Part of this rms is caused by panels that are far out and have one or more adjusters with certain error status that were not yet moved.
In February 2003 we got permission to attempt to move 28 of these adjusters (most of them have a wheel error while a wheel reference had been found).

This was done on 5 March 2003 based on a map made in grade 1/2 weather on 11 February (also all good motors were moved), and after these moves we tried to make a 160 GHz map. However unfortunately during this (daytime) map the humidity increased strongly and the map shows stripes - see this surface plot and the resulting rms is rather large (30-35 micron).
On 18 March 2003 another map was taken in grade 3 weather (tau225 about 0.12) which is somewhat better, but still shows some stripes (rms 23-30 micron).

Moves obtained from the maps before (made in grade 1/2 weather) and after these testmoves are compared in the figure below. Plotted are moves in steps (1 step is 3.26 micron) versus sector+motor/100.0 (sectors 1,12 are in the bottom of the dish, sectors 6,7 in the top).
Lower motor numbers are in the outer rings; higher motor numbers in the inner rings. It is seen that there is improvement for the 'faulty' adjusters that we tried to move on 5 March (plotted in blue), whereas the other faulty adjusters (red - most of them have phase errors), still show deviations (as expected).

The map of 18 March will not be used to adjust the dish. We plan to obtain a new map within the next week, and hope that the rms will be even better than the 20-24 micron of 11 February.

Last modified: 19 March 2003
Jan Wouterloot