aLIGO LHO Logbook

H1 SUS (AOS, AWC, DetChar, ISC, SQZ, SUS)

jeffrey.kissel@LIGO.ORG - posted 11:44, Friday 12 November 2021 - last comment - 10:37, Wednesday 19 January 2022(60632)

Calibration of HXDS Alignment Sliders Installed

J. Kissel

I've installed the calibrating pitch and yaw gains derived in LHO aLOG 60564 into to the M1_OPTICALIGN filter banks of all HXDSs, ZMs 1-6, which calibrates the OFFSET of the filter bank, which is used for DC alignment control, into units of microradians [urad].

    New : H1:SUS-ZM1_M1_OPTICALIGN_P_GAIN 0.6412
    New : H1:SUS-ZM1_M1_OPTICALIGN_Y_GAIN 0.8166

    New : H1:SUS-ZM2_M1_OPTICALIGN_P_GAIN 0.6412
    New : H1:SUS-ZM2_M1_OPTICALIGN_Y_GAIN 0.8166

    New : H1:SUS-ZM3_M1_OPTICALIGN_P_GAIN 0.6412
    New : H1:SUS-ZM3_M1_OPTICALIGN_Y_GAIN 0.8166

    New : H1:SUS-ZM4_M1_OPTICALIGN_P_GAIN 0.6412
    New : H1:SUS-ZM4_M1_OPTICALIGN_Y_GAIN 0.8166

    New : H1:SUS-ZM5_M1_OPTICALIGN_P_GAIN 0.6412
    New : H1:SUS-ZM5_M1_OPTICALIGN_Y_GAIN 0.8166

    New : H1:SUS-ZM6_M1_OPTICALIGN_P_GAIN 0.6412
    New : H1:SUS-ZM6_M1_OPTICALIGN_Y_GAIN 0.8166

HEADS UP: While there were some of these suspensions that had existing, requested, alignment offsets in units of DAC counts, I did not make an effort to restore the *actual* alignment of the suspension with the equivalent number of microradians. So if the alignment of yore needs to be recreated, just trend the former OPTICALIGN_P_OUTMON and/or P_OUTMON, and divide the values by the above calibration numbers, and then set the alignment sliders to that resultant, e.g. (former P_OUTMON) / (0.6412) = (desired new P_OFFSET).

I've captured these gains (as well as a corresponding a two, 2.0, second ramp) into the corresponding safe.snaps for these suspensions, which point to 
    /opt/rtcds/userapps/release/sus/h1/burtfiles/
        h1sussqzin_down.snap          (for ZM1, ZM2, and ZM3)
        h1sussqzout_observe.snap      (for ZM4, ZM5, and ZM6)
which have both now been committed to that location in the userapps repo.

Comments related to this report

sheila.dwyer@LIGO.ORG - 11:09, Wednesday 17 November 2021 (60673)

Link

Restored ZM5 alignment. 60672

jeffrey.kissel@LIGO.ORG - 10:33, Wednesday 19 January 2022 (61336)

Link

The thought process for turning the arc value into and angle value used in the above calculation (from reference LHO aLOG 60453) does not account for the infamous factor of 2 in optical-lever-style displacement measurements.

The calculations should not have used
    angle value = (arc value / lever value)

but instead 
    angle value = (arc value / (2 * lever value) )



See description of why this factor of two appears in G1200698.

Rather than redo all these calculations in the comments here, I'll just make a new aLOG.

jeffrey.kissel@LIGO.ORG - 10:37, Wednesday 19 January 2022 (61338)

Link

During these current few weeks of heavy alignment work (Jan 17 through Jan 28 2022), Sheila and I agreed that we should *not* fix these installed slider calibrations *yet*, but instead merely understand that they have flaws. 

I'll post a new aLOG once the corrected calibrations are calculated and installed.