J. Kissel, G. Moreno, K. Ryan, T. Sadecki, B. Shapiro, D. Sigg, B. Weaver, J. Worden

In summary
What happened today made little to no sense. If we continue to play this "mess with the environment, see what happens" game, we feel like we'll 
(a) Be at the game for a week or three, and
(b) Continue to fight the environment after the three weeks of fine tuning until we next vent for other reasons.
We (at least Betsy, Travis, Daniel, Brett, and I) vote for a "quick" in-and-out vent to fix the problem in hardware. 
We'll in discuss at tomorrow's morning meeting.


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What's brought us to this conclusion 
See first attached, 2015-01-06_ETMXAdventure_Annotated.pdf. It's a 24 hour trend of
(UL) The VEA temperature
(LL) The QUAD's vertical displacement
(UR) The fine vacuum pressure (good only when pressure is sub-[Torr])
(LR) The course vacuum pressure (good only when pressure is > ~0.1 [Torr])

Here's the timeline:
- (Beginning of the plot) We see the morning, where we've left the suspension. The VEA is at 19.5 [deg C], the pressure is still slowly falling, and roughly at 3.2e-7 [Torr]. 
- (Solid BLACK line) John decreases the temperature set point of the VEA. Don't see much change (maybe a *little* rise in the SUS).
- (Dot-dashed MAGENTA line) John makes a second adjustment, to account for the potential overshoot, or something . We begin is see the steady increase in displacement, lifting the SUS *up* for which we'd hoped. Yay! But... we see only ~2 [um] in 2 [hrs], and we know we have to go over 100 [um].
- We all had a hall-way conversation, and decided "let's burp in some dry air, to decrease the time constant, by increasing the thermal conductivity in the chamber." 
- (Double-dot-dashed RED line) Kyle burps in 0.5 [Torr] of dry air (see LHO aLOG 15893) -- at the region where (in the hallway) we convince ourselves there's enough air to become sufficiently conductive but below were buoyancy begins to have an effect. 
The SUS drops 15 [um] suddenly. 
     What? 
     Why? 
     More on this in a second.
Then ... over the next several hours the SUS continues to drop, at thermally slow rate. 
     What?? 
     Shouldn't the air have made the temperature equilibrate to lower faster, bringing up the SUS? 
     If not faster, at least at the same rate?

Comparison against the other SUS in the chamber that we know are free
See second attachment, 2015-01-06_H1BSC9SUS_DispComparison.pdf, which is a data viewer export of the vertical displacement for all three SUS in the chamber, except that I've removed the DC bias on all of them so that there change is more obvious. Remember, all of these SUS chains, the ETMX Main, ETMX Reaction, and the TMS, all have roughly the same overall suspended mass, because the Suspension Point blade springs and the top mass are all roughly copy-and-pastes of each-other.
We indeed see:
- The same upturn and increase of displacement when John turns down the VEA temperature in all three suspensions. Notice that the Reaction Chain and TMS rise at *the same rate* and differently than the main chain.
- All three suspensions see the ~15 [um] drop. We think we have an explanation for this, but again will say more later.
- The Reaction Chain and TMS start to slowly turn back up and rise in height again. Still -- at a slower rate than before (??), but at least they rise. And certainly look nothing like the Main chain.

Why the 15 [um] drop?
Daniel, smarter than us all, conjectures it's the OSEM's LED senstivity to temperature. We look at all 6 of the OSEMs on the M0 chain, and we see they all have a large just when the air is burped into the chamber. His theory: the ideal gas law, pV = nRT, tells us that increasing the pressure in the chamber increases the temperature. Though I don't think anyone has measured the OSEMs light output as a function of temperature, we can guess from a few internet sources (e.g. here, here, and here) that the sensitivity to temperature is roughly a 1-3% change in output per degrees C, where lower temperature means and increase in output power.  To the OSEM's PD, an increase in LED output power (from increased temperature, from increased pressure) looks the same as the flag being pushed out of the OSEM. For the vertical degree of freedom, the LF and RT OSEMs, which are on top of the TOP mass, pulling out of the OSEM reads that the SUS has sunk down. The OSEMs have a linear range of 700 [um]. 1-3% of 700 [um]? You guessed it: 7 - 21 [um].


Re-conlusion
So look -- if 
- we're chasing down and getting fooled by 1% temperature dependence of the OSEMs LEDs showing 15 [um], 
- changing the environment by 1 [deg C] only gets a change of a ~3 [um/hr] when we need more than 100 [um], and 
- the test mass (or the other chains for that matter) aren't doing what we'd naively expect, 
then we're barking up the wrong, very slow, very time consuming, tree that may be a dead end with not enough juice to get what we need anyway. 

Let's just go in and fix the problem by backing off the earthquake stops to 2 [mm], or 2000 [um]. Still plenty of protection from earthquakes, and we stop playing this horrible game with these horribly temperature sensitive suspensions.