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Entry  Wed May 15 00:40:19 2019, gautam, Update, SUS, ETMY diagnosis plan ETMY_sensorSpectra.pdf
    Reply  Wed May 15 10:57:57 2019, gautam, Update, SUS, EY chamber opened 
       Reply  Wed May 15 17:46:24 2019, gautam, Update, SUS, ETMY inspection firstContactFiber.JPGETMY_sensorSpectra.pdf
          Reply  Wed May 15 19:36:29 2019, Koji, Update, SUS, ETMY instepction 
             Reply  Thu May 16 13:07:14 2019, gautam, Update, SUS, First contact residue removal etmy_sensors.pdfetmy_BRmode.pdf
                Reply  Thu May 16 23:31:55 2019, gautam, Update, SUS, ETMY suspension characterization 6x
                   Reply  Fri May 17 17:01:08 2019, gautam, Update, SUS, ETMY suspension characterization etmy_oplevs.pdf
          Reply  Mon May 20 11:33:46 2019, gautam, Update, SUS, ITMY inspection 
             Reply  Mon May 20 17:12:57 2019, gautam, Update, SUS, ETMY LL adjustment 
                Reply  Mon May 20 22:06:07 2019, gautam, Update, SUS, ITMY also kicked 
                   Reply  Tue May 21 00:15:21 2019, gautam, Update, SUS, Main objectives of vent achieved (?) etmy_oplevs_20190520.pdfETMY_cplxTF.pdfETMY_diagComp.pdfScreen_Shot_2019-05-21_at_12.37.08_AM.png
                      Reply  Tue May 21 21:33:27 2019, gautam, Update, SUS, ETMY HR face cleaned 
                         Reply  Wed May 22 11:53:50 2019, gautam, Update, SUS, ETMY EQ stops backed out ETMY_eigenmodes.pdf
Message ID: 14615     Entry time: Thu May 16 23:31:55 2019     In reply to: 14613     Reply to this: 14620
Author: gautam 
Type: Update 
Category: SUS 
Subject: ETMY suspension characterization 

Here is my analysis. I think there are still some problems with this suspension.

Attachment #1: Time domain plots of the ringdown. The LL coil has peak response ~half of the other face OSEMs. I checked that the signal isn't being railed, the lowest level is > 100 cts.

Attachment #2: Complex TF from UL to the other coils. While there are four peaks now, looking at the phase information, it isn't possible to clearly disentangle PIT or YAW motion - in fact, for all peaks, there are at least three face shadow sensors which report the same phase. The gains are also pretty poorly balanced - e.g. for the 0.77 Hz peak, the magnitude of UR->UL is ~0.3, while LR->UL is ~3. Is it reasonable that there is a factor of 10 imbalance?

Attachment #3: Nevertheless, I assumed the following mapping of the peaks (quoted f0 is from a lorentzian fit) and attempted to find the input matrix that best convers the Sensor basis into the Euler basis.

DoF f0 [Hz]
POS 1.004
PIT 0.771
YAW 0.920
SIDE 0.967

Unsurprisingly, the elements of this matrix are very different from unity (I have to fix the normalization of the rows).

Attachment #4: Pre and post diagonalization spectra. The null stream certainly looks cleaner, but then again, this is by design so I'm not sure if this matrix is useful to implement.

Next steps:

  1. Repeat the actuator diagnonality test detailed here.
  2. ???

In case anyone wants to repeat the analysis, the suspension was kicked at 1828 PDT today and this analysis uses 15000 seconds of data from then onwards.

​Update 18 May 3pm:  Attachment #5 better presentation of the data shown in Attachment #2, the remark about the odd phasing of the coils is more clearly seen in this zoomed in view.  Attachment #6 shows Lorentzian fits to the peaks - the Qs are comparable to that seen for the other optics, although the Q for the 0.77 Hz peak is rather low.

Attachment 1: ETMY_sensors_timeDomain.pdf  49 kB  Uploaded Fri May 17 00:33:52 2019  | Hide | Hide all
ETMY_sensors_timeDomain.pdf
Attachment 2: ETMY_cplxTF.pdf  750 kB  Uploaded Fri May 17 00:53:56 2019  | Hide | Hide all
ETMY_cplxTF.pdf
Attachment 3: matrixDiag.png  14 kB  Uploaded Fri May 17 00:54:07 2019  | Hide | Hide all
matrixDiag.png
Attachment 4: ETMY_diagComp.pdf  67 kB  Uploaded Fri May 17 00:54:45 2019  | Hide | Hide all
ETMY_diagComp.pdf
Attachment 5: ETMY_cplxTF.pdf  370 kB  Uploaded Sat May 18 16:17:24 2019  | Hide | Hide all
ETMY_cplxTF.pdf
Attachment 6: ETMY_pkFitNaive.pdf  165 kB  Uploaded Sat May 18 16:24:35 2019  | Hide | Hide all
ETMY_pkFitNaive.pdf
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