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40m Log |
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Fri Apr 18 20:17:17 2014, Jenne, Update, LSC, ALS noisy 
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Mon Apr 21 22:53:16 2014, manasa, Update, LSC, ALS noise 
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Tue Apr 22 01:11:42 2014, Jenne, Update, LSC, TRY 60Hz noise
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Tue Apr 22 21:54:50 2014, manasa, Update, LSC, TRY 60Hz noise
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Tue Apr 22 22:49:10 2014, rana, Update, LSC, TRY 60Hz noise
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Wed Apr 23 19:58:00 2014, manasa, Update, LSC, TRY 60Hz noise
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Tue May 6 18:32:14 2014, steve, Update, LSC, TRY 60Hz noise hunt
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Wed May 7 14:01:36 2014, steve, Update, LSC, TRY 60Hz noise hunt
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Thu May 8 17:25:17 2014, steve, Update, LSC, TRY 60Hz noise hunt
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Fri May 16 16:08:12 2014, steve, Update, LSC, Isolating base plates
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Wed Apr 23 23:48:30 2014, manasa, Update, LSC, Y end whitening board  
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Thu Apr 24 14:23:09 2014, not manasa, Update, LSC, Y end whitening board
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Thu Apr 24 23:55:31 2014, Koji, Update, LSC, Y end whitening board
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Fri Apr 25 10:43:57 2014, Koji, Update, LSC, (Fixed) Y end whitening board   
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Thu Dec 11 18:12:46 2014, ericq, Update, LSC, (Fixed) Y end whitening board
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Thu Dec 11 22:44:23 2014, rana, Update, LSC, QPD screens
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Thu Apr 24 00:11:35 2014, Jenne, Update, LSC, Yend shutter back.
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Sun Apr 27 20:26:19 2014, Koji, Update, LSC, Phase Tracker servo characterization 
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Sun Apr 27 21:30:59 2014, Koji, Update, LSC, ALS servo characterization 
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Mon Apr 28 10:24:10 2014, Koji, Update, LSC, error signal characterization 
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Mon Apr 28 10:34:51 2014, Koji, Update, LSC, new ALS servo design 
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Mon Apr 28 10:48:48 2014, Koji, Update, LSC, new ALS servo design: comparison 
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Mon Apr 28 10:59:54 2014, Koji, Update, LSC, New ALS servo design: expected error signals 
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Mon Apr 28 11:08:11 2014, Koji, Update, LSC, New ALS servo design: expected error signals
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Message ID: 9836
Entry time: Mon Apr 21 22:53:16 2014
In reply to: 9832
Reply to this: 9838
9860
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Author: |
manasa |
Type: |
Update |
Category: |
LSC |
Subject: |
ALS noise |
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Quote: |
Last night, as well as tonight, the ALS seems not quite as robust as it was earlier in the week.
I have just taken noise spectra, and ALS is definitely more noisy than usual.
These plots are with the arms held in CARM and DARM mode, with servo gains of 8. I was seeing the beginnings of gain peaking at a gain of 10, so I turned it back to 8. Our ALS in-loop RMS is usually something like a few hundred Hz, but I'm seeing over 1kHz, so I have a factor of 4 or 5 too much noise. Why?!?!?
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I have noticed that ALS noise has been at 1KHz rms since LSC arm lock servos have been used to lock arms using ALS error signals. May be this has not been given much attention.
But looking more closely at the ALS noise (better dtt resolution for noise power spectrum) , there seems to be too much noise suppression at <1Hz and not much happening at around 10Hz.
Attachment 1 (data files at /users/manasa/data/140421/)
So I made a bunch of transfer function measurements for ALS and phase tracker servo. Koji will be using these and redesigning the servo filters so that we can get more suppression at 10Hz.
Other than this I also found that the Y arm showed more high frequency noise as compared to the X arm. (Edit by manasa: Thinking back now, this could be related to the onset of 60Hz noise at the Y end elog 9838. But still has to be looked at after fixing TRY)
Attachment 2
Tip: Once the arms are ALS locked, enabling the SLOW_SERVO helps hold the lock stably.
P.S. I realigned the Y green to the arm and brought GTRY to 0.93
To do:
Find out what makes Y arm in-loop noise at high frequency higher than X arm. |
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