Reports until 21:17, Monday 08 October 2018
H1 ISC (ISC)
craig.cahillane@LIGO.ORG - posted 21:17, Monday 08 October 2018 - last comment - 15:51, Tuesday 09 October 2018(44422)
Change power-up gain slider from LSC IN1 to IMC FAST to reduce glitch size 
Craig, Sheila

We have glitches in CARM associated with the discrete stepping of our analog gain sliders while we power up.  These are unavoidable, since we must compensate for the increase in optical gain by decreasing the analog gain by an equal amount, and we cannot use digital power normalization like for other LSC.
In order to reduce the size of the glitches, we have moved the stepping stage downstream, from LSC-REFL_SERVO_IN1GAIN to IMC-REFL_SERVO_FASTGAIN and LSC-MCL_GAIN.  

Our current gain settings are not optimal, but the glitches are lower than before: Sheila will post a follow-up confirming this.

We did this by changing what sliders the ISC_library.py function IMC_power_adjust_func() adjusts.  I also adjusted IMC_LOCK so the IMC locks with IMC IN1 at 25 dB now (this is increased by 3 dB from usual, another alog is in the works).  In any case, the guardian works now for both locking the IMC and powering up.

There are a total of 7 relevant gain sliders in the analog CARM path, along with two compensation filters (from the awiki pole/zero -- IMC: 40 Hz / 17 kHz, LSC: 40 Hz / 4 kHz ) and one boost (1 kHz / 20 kHz).  
Assuming these filters have a gain of 1 at AC, then at DC we get gains of:
IMC Comp DC Gain = 52.56 dB
IMC Boost Gain = 26.0 dB
LSC Comp DC Gain = 40 dB


CARM Gain Slider Values at 2 watts (at the end of Guardian states RESONANCE, CARM_TO_ANALOG, and ADJUST_POWER [at 10 watts])

ISC_LOCK State    SUM NODE A IN2    LSC IN1      LSC MCL GAIN    LSC FAST    IMC IN1    IMC IN2    IMC FAST   |  CARM FAST OVERALL    CARM SLOW OVERALL 
-------------------------------------------------------------------------------------------------------------------------------------------------------
RESONANCE                   2 dB     -16 dB     240 (47.6 dB)        7 dB      25 dB      -6 dB        0 dB   |             -13 dB              33.6 dB
CARM_TO_ANALOG            -12 dB      11 dB    53.8 (34.6 dB)        0 dB      25 dB     -12 dB        0 dB   |             -13 dB              33.6 dB
ADJUST_POWER [10 W]       -12 dB      11 dB    10.2 (20.2 dB)        0 dB      25 dB     -12 dB      -14 dB   |             -27 dB              19.2 dB


CARM FAST OVERALL = SUM NODE A IN2 + LSC IN1 + LSC FAST + IMC IN2 + IMC FAST 
CARM SLOW OVERALL = SUM NODE A IN2 + LSC IN1 + LSC MCL GAIN 
Neither "OVERALL" gain includes the gain of the filters.
Comments related to this report
sheila.dwyer@LIGO.ORG - 23:49, Monday 08 October 2018 (44424)
Link

The two attached lockloss plots show an attempt at powering up earlier today where every other gain step in the common mode board made a large glitch in the CHARD loops, and one of these caused a lockloss.  The second plot shows the same hard asc channels during a power up after this change, there is no glitch.  This was causing us to occasionally loose lock while trying to power up, but it looks like this fixed the problem. 

Images attached to this comment
daniel.sigg@LIGO.ORG - 08:33, Tuesday 09 October 2018 (44430)
Link

Gain slider combinations of -12dB followed by +11dB look like unity gain, but effectively loose 16dB of SNR.

craig.cahillane@LIGO.ORG - 15:51, Tuesday 09 October 2018 (44444)ISC
Link 

I altered the CARM_TO_ANALOG state gain sliding.  I have not tested the state since we are locked currently.
Steps 1 through 8 in CARM_TO_ANALOG are about transitioning from TR_CARM to REFL9I.  Step 8 completes the transition, and step 9 starts the gain redistribution.  I changed steps 9 and 11 such that we won't have such a drastic attenuation/amplification in the CARM loop without changing the overall gain.

Gain Slider Values after Step 8 in CARM_TO_ANALOG

Slider             Value
-------------------------------------------------
SUM NODE A IN2        2 dB
LSC IN1             -16 dB
LSC FAST              7 dB
IMC IN2              -6 dB
MCL GAIN           47.6 dB  (240 mag)


Old Gain Redistribution Steps, starting at step 9:

9)
LSC IN1 increased from -16 to 4 dB
SUM NODE A IN2 decreased from 2 to -18 dB

10)
LSC IN1 increased from 4 to 11 dB
LSC FAST decreased from 7 to 0 dB
MCL GAIN decreased from 47.6 to 40.7 dB

11)
SUM NODE A IN2 increased from -18 to -12 dB
IMC IN2 decreased from -6 to -12 dB
MCL GAIN decreased from 40.7 to 34.7 dB


New Gain Redistribution Steps

9)
Removed

10)
LSC IN1 increased from -16 to -9 dB
LSC FAST decreased from 7 to 0 dB
MCL GAIN decreased from 47.6 to 40.7 dB

11)
LSC IN1 increased from -9 to -3 dB
IMC IN2 decreased from -6 to -12 dB
MCL GAIN decreased from 40.7 to 34.7 dB


Predicted Gain Slider Values after new CARM_TO_ANALOG

Slider             Value
-------------------------------------------------
SUM NODE A IN2        2 dB
LSC IN1              -3 dB
LSC FAST              0 dB
IMC IN2             -12 dB
MCL GAIN           34.7 dB  (53 mag)