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
Message ID: 927     Entry time: Thu Sep 4 17:12:57 2008
Author: Yoichi 
Type: Update 
Category: PSL 
Subject: FSS open loop TF 
I changed the gain settings of the FSS servo.
Now the Common Gain is 5dB (the last night it was 2dB) and the Fast Gain is 12dB (formerly 16dB).
I measured the open loop TF with this setting (the attachment).
I also plotted the OPLTF when CG=2dB, FG=20.5dB. With this setting, the MC looses lock every 30min.

You can see that the OPLTF is smoother with FG=12dB.
When the FG is high, you can see some structure around 250kHz. This structure is reproducible.
This may be some interruption from the fast path to the PC path through a spurious coupling.
Attachment 1: FSS-OPLTFs.png  16 kB  | Hide | Hide all
FSS-OPLTFs.png
ELOG V3.1.3-