J. Kissel

[[[ EDIT -- The feature excited in the attached measurements is at 5.1 [Hz], NOT 6.1 [Hz]. I was reading the plot too quickly, had 6.1 [Hz] on the brain, and assumed it was 6.1 that I was ringing up. This 5.1 [Hz] feature is most certainly the last "transverse" mode (that has roughly equal components in L, R, and P as well), modeled to be at 5.08 [Hz].

Only configuration (3) shows anything at 6.18 [Hz]. In the other configurations, it is probably just that I'm only using one of two vertical sensors that excites roll motion -- which is NOT damped, because the R loop is open during these measurements.

Note, that this doesn't rule out that M0 LF has a problem. But it certainly makes concluding anything more complicated. 

Sorry for the confusion. Thanks to Dr. Lantz and J. McIver for reminding me how to read a logarithmic plot.]]]

Inspired by a suggestion of the good Dr. Lantz, I tried to further narrow down the source of the 6.18 [Hz] feature that has been plaguing H1 SUS ITMY. With the ISI still in it's best performing state, L,T,P, and Y SUS damping loops running, and the R loop off, I tried running the M0 (main chain) V SUS damping loops (which use the average of M0 LF and M0 RT OSEMs) with only M0 LF and only M0 RT OSEMs. I did this testing 5 different configurations:
(1) V loop open
(2) V loop closed with V to M0 LF OSEM2EUL element as zero (V to RT element at nominal -0.5, EUL2OSEM elements using both as nominal)
(3) V loop closed with V to M0 RT OSEM2EUL element as zero (V to LF element at nominal -0.5, EUL2OSEM elements using both as nominal)
(4) V loop closed with both V to M0 LF OSEM2EUL and EUL2OSEM elements as zero (V to RT elements at nominal -0.5)
(5) V loop closed with both V to M0 RT OSEM2EUL and EUL2OSEM elements as zero (V to LF elements at nominal -0.5)

Configurations (1), (2), and (3) are shown in the first attachment (*_0435_*.pdf), and configurations (1), (4), and (5) are shown in the second attachment (*_0521_*.pdf).

Configurations (1) and (4) did NOT show the 6.18 [Hz] feature, while configurations (2), (3), and (5) all showed the 6.18 [Hz] feature (plus various other mechanical modes and harmonics rung up as well). This directly points the finger at the M0 LF sensor/actuator.

Indeed, because the ISI input motion is so small, without the M0 LF OSEM in use, the *ENTIRE* spectra is limited by the expected OSEM sensor noise floor (see, e.g. configuration (1)). It's therefore blatantly obvious when the feature oscillates that it excites the whole suspension in many DOFs. If one squints, one *CAN* see the feature in all configurations, implying that wherever the source, it is visible in BOTH LF and RT sensors. In the configurations where the feature is not triggered into oscillation, it's only a factor a few above the noise floor, but it's still there. 

I'm not sure that this data set rules out the sensor, actuator, a nasty cross-coupling, or something else inherent to the motion of the suspension, but at least it narrows down the oscillation problem to one rogue OSEM.

Please swap out the M0 LFRT, R0 LFRT satellite amplifier tomorrow, and we'll test whether the feature disappears.