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Entry  Fri Dec 12 04:33:49 2014, Jenne, Update, ASC, ASS retuned 
    Reply  Wed Dec 17 01:51:44 2014, rana, jenne, Update, ASC, ASS retuned ASSconfig_141217_0205.png
       Reply  Wed Dec 17 19:04:12 2014, jenne, Update, ASC, ASS retuned 
          Reply  Wed Dec 17 19:31:55 2014, Koji, Update, ASC, ASS retuned 
             Reply  Tue Jan 27 21:33:39 2015, Koji, Update, ASC, ASS retuned 
Message ID: 10789     Entry time: Fri Dec 12 04:33:49 2014     Reply to this: 10807
Author: Jenne 
Type: Update 
Category: ASC 
Subject: ASS retuned 

[Rana, Jenne]

We decided that tonight was the night for ASS tuning. 

We started from choosing new frequencies, by looking at the transmission and the servo control signals spectra to find areas that weren't too full of peaks.  We chose to be above the OpLev UGF by at least a factor of ~2, so our lowest frequency is about 18Hz.  This way, even if the oplevs are retuned, or the gains are increased, the ASS should still function. 

We set the peak heights for the lowest frequency of each arm to have good SNR, and then calculated what the amplitude of the higher frequencies ought to be, such that the mirrors are moving about the same amount in all directions. 

We re-did the low pass filters, and eliminated the band pass filters in the demodulation part of the servo.  The band passes aren't strictly necessary, as long as you have adequate lowpassing, so we have turned them off, which gives us the freedom to change excitation frequencies at will.  We modified the lowpass filter so that we had more attenuation at 2Hz, since we spaced our excitation frequencies at least ~2.5 Hz apart.

The same lowpass filter is in every single demodulator filter bank (I's and Q's, for both length and transmission demodulation).  We are getting the gain hierarchy just by setting the servo gains appropriately. 

We ran ezcaservos to set the demodulation phase of each lockin, to minimize the Q-phase signal. 

We then tuned up the gains of the servos.  Rana did the Y arm, but for the X arm I tried to find the gains where the servos went unstable, and then reduced the gain by a factor of 2.  The Xarm is having trouble getting good alignment if you start with something less than about 0.7, so there is room for improvement.

Rana wrote a little shell script that will save the burt snapshot, if the gains need adjusting and they should be re-saved. 

The scripts have been modified (just with the new oscillator amplitudes - everything else is in the burt snapshots), so you should be able to run the start from nothing and the start from frozen scripts for both arms.  However, please watch them just in case, to make sure they don't run away.

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