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Entry  Wed Mar 11 16:53:48 2009, Yoichi, Update, Locking, Junks in around kHz MC_F-XARM.pdfold-xarm.pdf
    Reply  Wed Mar 11 22:57:48 2009, Yoichi, Update, Locking, Calibrated XARM error signal spectrum XarmErrorSpeCalibrated.pdf
       Reply  Fri Mar 13 22:07:14 2009, Yoichi, Update, Locking, Calibrated XARM error signal spectrum XarmErrorSpeCalibrated.pdf
Message ID: 1388     Entry time: Wed Mar 11 16:53:48 2009     Reply to this: 1390
Author: Yoichi 
Type: Update 
Category: Locking 
Subject: Junks in around kHz 
Rana, Yoichi

Last night, we tried to find out the source of the kHz region peaks in the DARM and CARM error signals.
These peaks are also present in the error signal of the single arm locking by RF (both X and Y).
The attachment 1 shows spectra of MC_F and XARM error signal when XARM is locked by the POX PDH signal.
There is a sharp peak at 3.8kHz in MC_F. This peak was there in a reference spectrum taken on June 24 2008.

In the XARM error signal, there is also a broad peak around 3.8kHz. This peak moves between 3.75kHz and 3.8kHz from time to time.
(the brown curve was taken when the peak moved to 3.75kHz).
Also there is a notch like structure at 3.8kHz in the XARM error spectrum. Looks like the peak in the MC_F is creating a notch here, but
no idea why.

We tapped on the PSL table, the end chambers and the SPOB table and looked at the spectra to see if there is any change.
Rana also developed a cool Walkie-Talkie excitation technique, where he put one of the walkie-talkies on the PSL table by the MZ and yelled at the other one while looking at a DTT screen in the control room.
None of these had any effect on the XARM error, while MC_F responded to the disturbances.

We also turned on and off the steering mirror PZT closed loop buttons, moved the PMC, MZ and the ISS gain sliders and changed the MC gain, offset.
Nothing affected the XARM error.

Osamu found old spectra of the XARM signal (attm2). The legends say DARM but these are XARM signals.
Almost the same structures can be seen including the notch at 3.8kHz. Seems like it's been like this for long time.

We should check, RF-AM, MC coil dirivers, Piezo-Jena noise etc.
Attachment 1: MC_F-XARM.pdf  81 kB  | Hide | Hide all
Attachment 2: old-xarm.pdf  19 kB  | Hide | Hide all
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