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Entry  Fri Dec 7 19:24:43 2012, Den, Ayaka, Update, SUS, oplevs as acoustic and seismic noise couplers at high frequencies IMG_0111.JPGIMG_0112.JPGETMY_olreso_copy.pngYARM.png
    Reply  Fri Dec 7 20:34:31 2012, Ayaka, Update, SUS, oplevs as acoustic and seismic noise couplers at high frequencies YARM_acous_oplev.pdf
Message ID: 7798     Entry time: Fri Dec 7 19:24:43 2012     Reply to this: 7799
Author: Den, Ayaka 
Type: Update 
Category: SUS 
Subject: oplevs as acoustic and seismic noise couplers at high frequencies 

We've provided acoustic excitation using speakers on the AS table and saw that PSD of YARM feedback signal increased in the frequency range 50 - 100 Hz. Meanwhile, XARM feedback signal did not change. Moreover, YARM noise is much higher at these frequencies compared to XARM.

The problem was with YARM oplev servos. Both ITMY and ETMY produced noise to YARM length. ITMY oplev signal had a huge resonance at 55 Hz. We measured coherence with accelerometers, it was 0.8. It turned out that one of the mirror mounts was not fixed in the oplev path. When we fixed it, noise has gone.

Note: speakers were on AS table but mirror mounts could steel feel it on ITMY table.

IMG_0111.JPG         YARM.png

Then we had a look on ETMY table. We saw a mirror on suspiciously long mirror mount that was used in the ETMY oplev path. We slightly kicked long mount with a small screwdriver and YARM control signal went up with resonance at 100 Hz.

IMG_0112.JPG        ETMY_olreso_copy.png

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