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Entry  Tue Nov 15 12:25:38 2011, kiwamu, Update, Green Locking, Y arm ALS : beat-note free run fluctuation noise_budget.png
    Reply  Wed Nov 16 17:29:46 2011, kiwamu, Update, Green Locking, Some updates on the Y end green PDH Yarm_fluctuation.png
       Reply  Thu Nov 17 17:21:22 2011, kiwamu, Update, Green Locking, Y end green PDH servo : it's okay servoTF.pngservofilter.pngerr_suppression.png
          Reply  Fri Nov 18 11:28:39 2011, rana, Update, Green Locking, Y end green PDH servo : it's okay 
             Reply  Fri Nov 18 12:11:24 2011, Zach, Update, Green Locking, Y end green PDH servo : it's okay 
    Reply  Thu Nov 17 18:20:26 2011, kiwamu, Update, Green Locking, Y arm ALS : 1st trial of noise budget Yarm_ALS_2011Nov16.png
       Reply  Mon Nov 21 16:08:04 2011, kiwamu, Update, Green Locking, 2nd trial of Y arm ALS noise budget : broad band noise gone Yarm_ALS_2011Nov19.png
          Reply  Tue Nov 22 15:18:18 2011, kiwamu, Update, Green Locking, broad band noise depends on the gain of Y green PDH. and comaprator broken 
Message ID: 5978     Entry time: Tue Nov 22 15:18:18 2011     In reply to: 5970
Author: kiwamu 
Type: Update 
Category: Green Locking 
Subject: broad band noise depends on the gain of Y green PDH. and comaprator broken 

Quote from #5970
Here is a plot of the latest noise : high frequency noise is still unknown.

(The broad-band noise vs. gain of the Y end green PDH)

 Last night I was trying to identify the broad band noise which is white and dominant above 20 Hz (#5970).

I found that the level of the noise depended on the servo gain of the Y end green PDH loop.

Decreasing the servo gain lowers the noise level by a factor of 2 or so. This was quite repeatable.

(I changed the gain knob of the PDH box from the minimum to a point where the servo starts oscillating)

 

(Malfunction in the comparator)

  However I had to give up further investigations because the comparator signal suddenly became funny: sometimes it outputs signals and sometimes not.

It seems the comparator circuit became broken for some reason. I will fix it.

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