[Kiwamu, Paul]
Just before the vent today we measured new noise spectra for the frequency and length feedback paths.
The 'whitening filters' in the IMC_X path (see Giacomo's LHO alog entry 5311) were not engaged. They were put in the model at LLO in an attempt to combat the digital noise in IMC_X above ~50Hz (see Anamaria's LLO alog entry 5821) but need to be taken account of when plotting the data.
We corrected the IMC_F frequency to length calibration to give the equivalent motion of MC2, instead of the equivalent round trip length change. This has now been edited in the filter bank for the IMC_X path; the FtoL filter has been changed to a DC gain of 5.8465e-14 (dX=df x lambda/(2FSR)).
Relevant paramters during the measurement:
Common mode gain 20dB
Common mode filters: Compensation and 1st Boost
Fast gain -2dB
Slow path bypassed offsets and filters
MC2 M3 lock gain -1000, engaged filters: 150:4 and CLP100
MC2 M2 lock gain 0.06, engaged filters: 0.01:0.1, 0.03:1, Stab8:2, 300:1 and ELF80
Damping filter: resg and Ellip50 (the filter in IMC_X path was switched to the wresg filter to reflect this change)
Jeff quite rightly pointed out that there are actually 2 more filter banks in the length path for the IMC which I didn't mention in the above post.
One of these is the H1:IMC_L bank, with the following 3 filters engaged and with Gain=1: antiWhite, roll3notch and bouncenotch.
The other bank is the H1:LSC-IMC bank, with 1 blank filter engaged with Gain=1. I'm not sure yet what the purpose of this bank is but would happy to know if someone else does! I'll try to get a signal flow chart up here soon, though it may be a little trickier from off-site.
I was revisiting this measurement and I thought it might be useful to add the PSL frequency noise requirement line for comparison (see attached).