Reports until 18:51, Tuesday 11 February 2014
H1 SUS
brett.shapiro@LIGO.ORG - posted 18:51, Tuesday 11 February 2014 - last comment - 09:20, Tuesday 18 February 2014(9999)
ETMX longitudinal modal damping filter installed 
I temporarily installed a modal damping filter on the longitudinal degree of freedom of ETMX. The filter has 32 poles, so it is split between two modules, 'md_part1' and 'md_part2'. I plan to measure ringdown times of the test mass tomorrow using the green cavity signal. This is part of an effort to see what are the fastest possible ringdown times of the test mass with top mass damping. After the test I will remove the filters.

Normally a modal damping filter wouldn't need this many poles, but I decided to include the pitch dynamics in the estimator to get a more faithful reproduction of the 1st longitudinal mode frequency for this test.
Comments related to this report
brett.shapiro@LIGO.ORG - 09:16, Tuesday 18 February 2014 (10132)
Link 

Measured results taken last wednesday. See the attachment. The damping on each mode was set so that each would ring down to 1/e in about 9 seconds.

The first page shows the measured and modeled closed loop top mass to top mass transfer function with the longitudinal DOF damped modally. The next 3 pages shows the measured and modeled impulse responses of the UIM, PUM, and testmass respectively. The impulse is injected into the top mass with the test excitations, the measurement is taken with the OSEMs at the UIM and PUM and the green cavity at the test mass. The impulse was set so that it was faster the the highest frequency longitudinal mode.

The measurements and model agree quite well. In the ringdowns there is a noticeable phase shift by the end of the 20 seconds because the model has not been fit to the ETMX yet. The cavity measurement also has some extra error becuase the cavity had large drifts and it was difficult to get enough signal without unlocking the cavity.
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brett.shapiro@LIGO.ORG - 09:20, Tuesday 18 February 2014 (10134)
Link 

Same plots but against the new fit of the ETMY model (and this is actually on ETMX). Also included are the number of seconds it takes to get to 1/e of the maximum.

I also tweaked the modeled pitch damping filter to make the first pitch mode have similar damping to the measurement. I didn't write down what the actual pitch damping filter is, so this is just a guess. This helps the cavity ringdown match the measurement more precisely. The pitch damping has a non-negligble influence on the cavity ringdown, since the first pitch mode is so close to the first longitudinal mode.
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