40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Tue Dec 10 15:13:55 2013, Koji, Update, IOO, IMC servo inspection 
    Reply  Thu Dec 12 14:57:01 2013, Koji, Update, IOO, IMC servo inspection OLTF_IMC.pdfAOTF_IMC.pdf131209.zip
       Reply  Fri Dec 13 18:03:00 2013, Den, Update, IOO, common mode servo CM_OL.pdfCM_CL.pdf
          Reply  Fri Dec 13 23:07:04 2013, Koji, Update, IOO, common mode servo 
          Reply  Sat Dec 14 11:56:54 2013, rana, Update, LSC, common mode servo 
             Reply  Sat Dec 14 14:21:46 2013, Den, Update, LSC, common mode servo 
Message ID: 9472     Entry time: Sat Dec 14 11:56:54 2013     In reply to: 9468     Reply to this: 9474
Author: rana 
Type: Update 
Category: LSC 
Subject: common mode servo 



 It seems to me that current design of the common mode servo is already fine. Attached plots show common mode open and closed loop transfer function.

 These seem like pretty terrible loop shapes. Can you give us a plot with the breakdown of several of the TFs and some .m file?

We should be able to estimate the noise coming out of the MC using the single arm and then make a guess for the CM loop gain requirement. There's no reason to keep the old Boost shapes; those were used in the old MC configuration which had a RefCav. In addition to minimizing the EOM range, we should also minimize the AO signal as Koji has pointed out. In practice, I've seen that using ~300 Hz of offset makes no harm with 4 kHz MC pole.

ELOG V3.1.3-