J. Kissel, B. Weaver, T. Shaffer

I've
- measured a new charge data point for 2016-04-26.
- processed all measurements that had not been processed over the past few months of measurements
- fixed the NDS problems that Betsy and TJ had been having preventing them from plotting the trend of the effective bias voltage

As such, it has now become blatantly obvious that between the last time we intentionally flipped the bias voltage on both ESDs in order to mitigate charge accumulation (on Feb 15th; see LHO aLOG 25575) both ETM ESDs have had their settings reverted within a month of the flip, and are now continuing to charge in the wrong direction. Further, it looks like the ETMY ESD bias voltage was reduced by half (albiet still on the wrong direction) somewhat recently on Apr 14th. What's even more worrisome is that neither the ETMY LOCK gain nor DRIVALIGN gain -- which should be used to compensate for the strength change resulting from a reduced bias -- were changed when it was reduced. At least, it appears as though that as we've been commissioning ASC stuff for the past month or so, we haven't been transitioning to ETMY anyways, so it may not have mattered (*phew*) and also why it has gone relatively unnoticed.

As such,  we should re-flip the bias sign on both ETMs, to what we flipped them to on February and I recommend with flip EY back to the larger value of bias voltage, so that the opposing sign of charge accumulates and the net charge decays back towards zero faster. 

I've done a good bit of aLOG, snap file time-stamp, and EPICs records sleuthing and have conclude that the flips were unintentional settings loss, as a result of us having SAFE, DOWN and OBSERVE.snap files in concert with several h1susetm[x,y] model restarts that were unplanned or after-thoughts (namely the HWWD install LHO aLOG 25860; and PI model install LHO aLOG 26200). No one is to blame here, it's just a testament to how hard it is to track and control settings during heavy commissioning, especially when we need to make a decision on how many of the three of the SDF files need updating.

Kiwamu concisely summarizes the steps to flipping the bias in LHO aLOG 25575, and we'll work with the commissioning team to do so as soon as conceivably possible. However, what Kiwamu failed to mention is that we need to update the H1SUSETMX, H1SUSETMY, and H1CALCS SDF snap files, and do so in the SAFE, DOWN, and OBSERVE snap files.

Attached are the charge trends and a zoom of when the EY bias was reduced on Apr 14th.