J. Kissel

I've turned on the calibration lines that are injected into the DARM loop. Their frequency has been pre-chosen to be 34.7 and 538.1 [Hz] (see selection criteria from LLO aLOG 15870). For their amplitude, instead of going through the rigor of reverse-calibrating exactly the right amplitude in DARM_CTRL [counts] to get exactly a line of x [m] in DELTA L EXTERNAL to get an exact SNR of 30, I've just copied the amplitude Joe had chosen for comparable L1 sensitivity during ER6 (see LLO aLOG 15944).


Details:
- Important parameters of the line:
                       Channel                                    Parameter                   Value        Purpose
Line 1    H1:CAL-CS_GAMMA_LINE1_DEMOD_OSC_CLKGAIN    Line Amplitude (in DARM_CTRL [ct])    0.0112 [ct]     To track the DARM OLGTF near the UGF
          H1:CAL-CS_GAMMA_LINE1_DEMOD_OSC_FREQ       Line Frequency                         34.7 [Hz]      

Line 2    H1:CAL-CS_GAMMA_LINE2_DEMOD_OSC_CLKGAIN    Line Amplitude (in DARM_CTRL [ct])    0.957 [ct]      To track changes in the DARM Coupled Cavity Pole Frequency
          H1:CAL-CS_GAMMA_LINE2_DEMOD_OSC_FREQ       Line Frequency                         538.1 [Hz]
Attached is a desktop capture of the relevant screens. Where you actually enter in / change these important parameters is on the green-backgrounded DEMOD screens.

- The computation of the optical gain calibration is still off / zero, because I haven't entered in the values for the reference open loop gain at the line frequency (and various other dams are shut along the path to actually have it correct the DARM sensing function).

- All of the new optical gain compensation EPICs records had *not* been monitored but the SDF system, because the new channels did not, by default, have their SDF mask bits set to unity. So, I have to use sdf_set_monitor to turn on all the new bits in 
/opt/rtcds/userapps/release/cal/h1/models/h1calcs_safe.snap
and then update the table (only) for them to be monitored, and then I captured a new safe SDF file with all of the settings as shown in the screenshot.

- I've checked a 10 [Mpc] reference spectra from March 27th 2015 -- the 10 [hour] lock stretch, so I could get 1 [mHz] resolution -- for features at these calibration line frequencies. Nothing there! *phew*. See attached screenshots of "Reference DARM;" both the full spectra, and the zooms at 34.7 and 538.1 [Hz].

- After lots of hemming and hawing about the bandwidth of the DEMOD's signal bandpass and frequency of the DEMOD's demodulated outputs' low-pass, I decided to just try something "reasonable," and acknowledge that we'll have to iterate. As such, I chose a 1 [Hz] bandwidth for the band-pass and a corner frequency of 0.01 [Hz] for the lowpasses. The exact foton design strings are:
Band passes (4th order chebychev bandpass, with 1 [dB] ripple, with 1st and 2nd frequencies as defined below)
cheby1("BandPass",4,1,34.2,35.2)
cheby1("BandPass",4,1,537.6,538.6)
Low passes (3rd order elliptic low pass, with 1 [dB] ripple, with 40 [dB] stop-band suppression, with a corner frequency of 0.01 [Hz])
ellip("LowPass",3,1,40,0.01)
I attach bode plots.

- Things you only find out when you turn things on: the MEDM display of some critical channels like the line amplitude were displayed on the screen in the "truncated" format. That means that numbers less unity don't show up! This is obviously yuck, since the calibration line amplitudes are less than one DARM_CTRL counts. So, I've updated the 
userapps/release/cal/common/medm/CAL_CS_GAMMA_LINE_OVERVIEW.adl
userapps/release/cds/common/medm/LOCKIN_DEMOD.adl
MEDM screens to display a precision of either 3, 4, or 6 sig figs beyond the decimal by default, and committed to the repo.