J. Kissel

Rahul and I missed the memo in the work permit to only measure the output arm, so I've started running through the mode-cleaner SUS, H1 SUS MC1, MC2, and MC3 to make sure they're healthy after the vent. 
I argue that there are several reasons to measure these SUS again, even though we didn't mechanically mess with them in chamber over the course of this long 2021 vent.
    - We've completely replaced / upgraded their IO chassis (during this process there have been some sneaky failure modes)
    - We've upgraded the RCG
    - Some of these haven't been measured since early 2020 when their were confirmed issues with BIO chassis
    - It's good to remind ourselves of the history of each suspension every year-or-so, make sure the library of measurements is well maintained
    - It gives us an excuse to "improve our characterization infrastructure as we go" e.g. 
        - this aLOG will be the first time we'll see the phase of transfer functions in the HSTS comparison plots.
        - some of the templates' excitation amplitudes were saved too large (namely, MC2's), and while though not saturating results cause lack of coherence. So now the nice amplitudes that have been used on MC1 and MC3 are now saved in the MC2 template.
        - I've also made sure that all templates are using 0.02 Hz frequency resolution, to help speed things along
        - I've also added M2 and M3 WIT channels, and made the M1_DAMP_IN1 channels all "A" channels such that now will have M1 to M2 and M1 to M3 transfer functions saved in the can.
    - We never know when the *next* thing to go wrong with the SUS will be -- or even when it'll be identified, so it's good practice to keep up a ~once a year cadence on these even if they never go wrong.

MC1 Story
allhstss_2021-12-07_1954_H1SUSMC1_Phase3b_UnDamped_M1_ALL_ZOOMED_TFs.pdf
MC2 is easy -- it continues to look healthy with no major signs of abnormality since at least 2017. 

MC2 Story
allhstss_2021-12-07_2031_H1SUSMC2_Phase3b_UnDamped_M1_ALL_ZOOMED_TFs.pdf
MC1's most recent malady is it's M1 T1T2T3LF binary IO switch went bonkers in 2020 -- see IIET Ticket 16047, and as a result that coil driver was replaced on 2020-10-28 (see LHO aLOG 57140). Then, Rahul measured these same transfer functions *after* the swap on 2020-10-29, so there was no "official" transfer function record that this happened. But -- it looked health after the swap in the 2020-10-29, and it continues to look health today. 

I will note that one might get immediately alarmed by the apparent reduction in Q of the L to L transfer function against previous results, but I confirm that this is a result of poor on-resonance coherence that we typically see coupled with the reduction of frequency resolution from 0.02 Hz to 0.01 Hz. This goes for the apparent mode splitting seen in the P to P transfer function too.

MC3 Story
allhstss_2021-12-07_2105_H1SUSMC3_Phase3b_UnDamped_M1_ALL_ZOOMED_TFs.pdf
MC3 is actually a positive one -- we had never measured a full set of TFs after the 2020-11-02 AI chassis swap (LHO aLOG 57179) fix to former AI Chassis' drive level issue (LHO aLOG 16116). That lower drive in the T3 coil resulted in subtle coil *unbalancing* of the degrees of freedom that use T3 -- V, R, and P -- and it manifested worst in the P to P transfer function which showed much more highest V and R mode cross coupling than usual, but also manifested in the R to R, and made the V to V TF drop in overall magnitude (because there was one less actuator driving vertical). This problem had actually been present since before 2020-04-15, but had gone unnoticed, or at least not understood (see LHO aLOG 60764). But indeed, today's measurements confirm that the T3 driver has been restored to normal function and actuation strength, and extra cross-coupling and magnitude drops have been relieve, making MC3 behave like a normal HSTS again.

(Keita's LHO aLOG 57172 helped remind me of all these MC1 and MC3 issues.)

MC1, MC2, and MC3 have regained their health after the pandemic, and all look good now.

I'll attach the SUS to SUS comparison plots first, and then upload the individual measurement plots which show cross-coupled off diagonal DOFs and response in the OSEM basis and cite the measurement templates in the comments below.