aLIGO LHO Logbook

H1 SEI

hugh.radkins@LIGO.ORG - posted 09:30, Wednesday 18 December 2013 - last comment - 14:46, Wednesday 18 December 2013(9001)

LHO ITMY & ITMX SEI ISI CPSs off for test ~2 hours

We've turn the two test mass Capacitive Position Sensors off to investigate the comb feature seen at LLO and possibly starting to reveal itself at LHO. The thought is that all the CPSs have their own master timing for each chamber and the individual chambers may be beating against one another.

We'll restore these in a couple hours.

Comments related to this report

fabrice.matichard@LIGO.ORG - 14:46, Wednesday 18 December 2013 (9007)SEI

Link

Looks like we do have combs due to cross talks between the oscillators of the CPS electronics. The beating base frequency is around 30 mHz (a factor of 10 below what has been observed at LLO).

In the plot attached:

- The top left plot shows the BSC-ISI Stage-1 Horizontal-1 CPS in the BS chamber. In the blue curve measurements, the CPS electronics of adjacent chambers (ITMX and ITMY) were turned off. In the red curve measurement, they were on. (Isolation and damping off for both measurements)

- The bottom left plot shows similar measurements and results for the BSC-ISI Stage-2 Horizontal-1 CPS in the BS chamber. (Isolation and damping off for both measurements)

- The top right plot shows a measurement with the ISI damping ON, which shows better the 30 mHz pics and harmonics.

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