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:
- Repeat the actuator diagnonality test detailed here.
- ???
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. |