J. Kissel, N. Lecoeuche, C. Vorvick

While clearing out SDFs prior to this observe segment, we found that PRM showed a DIFF with its OBSERVE.snap regarding the state of the switchable coil driver response. 

Cheryl spoke of this recently, in LHO aLOG 50273, whom was merely following Corey's lead who accepted the coil driver state response to be in State 2 LHO aLOG 50257.

A bit of education: even though we do not request any use of the M2 stage of PRM while in NOMINAL_LOW_NOISE (which gives the impression that "it doesn't matter what state we're in for observation"), the DAC channels that are connected to this stage still does emit a constant level of voltage noise, which -- in some of the switchable states, not all -- the coil driver is designed filter out that non-zero voltage noise.

A reminder: PRM is a "recycling cavity HSTS" whose M2 and M3 coil drivers have both been modified to increase their drive ability by reducing the output impedance (and thus allowing more of said DAC noise to be turned in to current by the driver). The state machine diagrams that reflect the response for this type of driver are found under T1100507, specifically that for the MODified Triple Acquisition driver:
    State 1 does "nothing," and passes through the voltage with only a fixed trans-conducance of ~3 [mA/V[.
    State 2 engages the switchable "acquire" circuit response of a gain-of-5x boost above 13 Hz.
    State 3 engages the switchable "low-pass" circuit response of a factor-of-ten reduction between 1 and 210 Hz
    State 4 is a weirdo state that engages both the acquire and low-pass resulting in a lumpy low-pass of 10, and a gain of 5.

So -- we want state 3 when in nominal low-noise such that we get as much filtering of the DAC noise as possible.

BUT -- there are several things weird here.
(1) Cheryl and I've double checked her plot that showed that the state was semi-regularly changing, but we can't reproduce her data. Both ndscope and dataviewer confirm that this state *rarely* changes, and only intentionally by the commissioning team (e.g. when we need extra drive to excite bounce and roll modes a. la. LHO aLOG 49643). The last time this happened was on May 28th, and we can confirm that we *do* see that change, it was quickly changed back after the testing was complete, and it has been in State 3 since, as it should be.
(2) This state is not changed during any of the lock acquisition sequence.

So -- it's unclear why this is showing up in SDF, or why on June 27th -- a month later -- it shows up for Corey as an SDF DIFF.

But -- the message -- We want State 3, so if anyone sees the SDF claim it should be 2 in the future please aLOG it and let me know.