J. Kissel

Gathered H1SUSPRM M3, M2, and M1 Drive to M1 Response TFs to inform the "drive" models for a future H1SUSPRM estimator. I'll post the locations / file names in the comments. Here in the main entry, I discuss the state of the control system for H1 SUS PRM so we understand with how much salt would should take these measurements.

Executive summary :: there are some side quests we can launch -- especially on the actuation side of this suspension -- if we think that these measurements reveal "way too much cross coupling for an estimator to work." The first things I'd attack would be 
    - the frequency-dependent and scalar gain differences *between* the nominal low noise state of the coil drivers and the state we need to characterize the suspension. 
    - the very old coil balancing, which was done *without* first compensating for any frequency-dependent gain differences in the channels at the frequency used to balance the coils (see LHO:9453 for measurement technique.)

Here's the detailed summary of all the relevant things for these measurements:
    - The suspension was ALIGNED, with alignment offsets ON, with slider values (P,Y) = (-1629.783, -59.868) ["urad"] 
        :: ALIGNED is needed (rather than just DAMPED [where the alignment sliders are OFF] or MISALIGNED where extra large alignment offsets are ON; per discussion of how the alignment impacts the calibration in LHO:87102)
        :: the usual caveats about the slider calibration, which is still using the [DAC ct / "urad"] gains from LHO:4563).

    - The M1 damping loop were converted to Level 2.0 loop shaping in Jan 2023; LHO:66859, nominally designed to have an EPICs gain of -1.0. However in Aug 2023, the EPICs gains were lowered to -0.5, and have been that way for most of O4, and remain that way now. For all of these measurements, I set the L, P and Y gains to -0.1; the "20% of nominal" gain mantra we've used for the HLTS estimators. I also gathered *almost* all the measurements again with only the Y gain at -0.1, but ran out of time to complete that set for comparison. 

    - Even though it was maintenance day, when we typically turn site-wide sensor correction OFF, I manually turned ON sensor correction for ISI HAM2 to get better coherence below 1 Hz (using instructions in LHO:87790)

    - The M3 L to M3 P filter (and gain) in the M3 DRIVEALIGN frequency-dependent matrix is OFF, per LHO:87523. 

    - There are (M3 P to M3 L) = 1.7 and (M3 Y to M3 L) = 0.52 scalar gains ON in to off-diagonal elements of the M3 DRIVEALIGN matrix whose purpose is change the center of P and Y actuation to be around where the IFO's beam spot typically is.

    - There is a set of M1 L to M1 P filters, "M1L_M3P" and "invM1P_M3P," in the M1 DRIVEALIGN matrix, with a EPICs gain of -1. I think these came from LHO:42549. The measurements I took aren't impacted by this, as I drove from the M1 TEST bank which does not send excitation through the DRIVEALIGN Matrix. HOWEVER, we'll definitely need to consider this when we model the ISC drive which *does* go through the M1 DRIVEALIGN matrix.

    - All M1, M2, and M3 stages of OSEM PDs sat amp whitening filters have been upgraded with ECR E2400330's filter design, and compensated accordingly. 
        :: M1 stage LHO:85463
        :: M2 & M3 stages LHO:87103

    - All M1, M2, and M3 stages of OSEM PDs have been calibrated via the ISI GS13s, and calibrated in the ALIGNED state (LHO:87231)

    - In order to get decent coherence over the band of interest for the M3, M2, and M1 drives, I had to drive the suspension actuators in their highest range state, which is different from the state the IFO usually needs.
        :: M1 = State 1 "LP OFF" (a Triple TOP Driver)
        :: M2 = State 2 "Acq ON, LP OFF" (An ECR E1400369 Triple Acquisition Driver "TACQ" modified for an extra 10x actuation strength. Modified in Sep 2013 LHO:7630)
        :: M3 = State 2 "Acq ON, LP OFF" (An ECR E1400369 Triple Acquisition Driver "TACQ" modified for an extra 10x actuation strength. Modified in Sep 2014 LHO:13956)

        :: The nominal state for the switches are M1 = State 2 "LP ON," M2 = M3 = State 3 "ACQ OFF, LP ON."

    - No actuator channels have had any precise compensation for their coil driver's frequency response in any state.
        :: M1 state 1 channels are all compensated with (z:p) = (0.9 : 30.9996) Hz
        :: M2 state 2 channels are all compensated with (z:p) = (64.9966 : 13) Hz
        :: M3 state 2 channels are all compensated with (z:p) = (64.9966 : 13) Hz

    - There are scalar "coil balancing" non-unity magnitude gains on each of the M2 and M3 stage channels, but it's the same values that have been in play since Jan 2014 (LHO:9419; so, after the M2 TACQ driver mod, but before the M3 TACQ driver mod). There is no coil balancing gains on the M1 stage, they're all either +/- 1.0.