Today I measured the sensing noise of ALS again, with enough amplification before the singa is sampled by ADC.

= How to measure =
Described in 7546

= Results =
The current RMS of the sensing noise times X arm cavity LPF is 13 Hz.
0.45 Hz peak contributes to the RMS the most, which has high coherence (> 0.7) with PR2 BF or TM signals.

= Note =
During this measurement, I stopped all the FFUs around MC, PR, and BS areas, KOACH filters for PSL room, and one precise air conditioner (PAC) for PSL room.
After this measurement, I stopped all the PACs for PSL room and saw if how the spectra change.
Here is the comparison; green: one PAC off, red: two (all) PAC off.
As can be seen the structure at ~ 22 Hz and ~ 50 Hz vanishes if you turn off all the PAC.
In fact, the ALS noise has a high coherence (> 0.9) with PSL-MIC signal when one PAC is on (see the last figure).
I did not measure the spectra with two PACs off, though. I did not want the temp in PSL room to drift away too much.