I assume you checked - Orientation of the gauge is important since it depends on convection at these pressures. 

Here are a few more pics.  As TJ notes, the ROC front face is 5-6mm from the SR3 AR surface.  It is locked down in this location. 

Note, we followed a few hints from LLO's install:

https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=25831

Continuity checks at the feedthru still need to be made.  Will solicit EE for their help.

Initial continuity test failed. Found issues with in-vacuum cable, power pins not pushed in completely. Pins were pushed in until a locking click was heard.

Reading are:
Larger Outer Pins, Heater: 66.9Ω
Inner pair (left most looking at connector from air side), thermacouple: 105Ω

Found center of SR3(-X Scribe) to be 230.2mm above optical table.  By siting the top and bottom of RoC Heater, found center to be at 231.4mm. Removed available shim to put center of RoC Heater at 229.6 for 230.2-229.6=0.6mm below perfect.

Hugh's comment reminded me that to get the heater to fit, Betsy and I added a 1mm washer to raise the height of the assembly. In total we have 4mm of washers (2x1.5mm & 1x1mm).

I conducted measurement of quantity 6 of [D1600104 SR3 ROC Actuator, Ceramic Heater Assy] at CIT on 4 March 2016. Dirty state before baking.
The serial number of the heater assy installed in LHO HAM5 is S1600180 - see https://ics-redux.ligo-la.caltech.edu/JIRA/browse/ASSY-D1500258-002
S1600180 Resistance = 66.8 Ohms on 4 March 2016.
There is good agreement between the as-installed and pre-bake measurements.

here is a wiki page to show how ellipses and circles can be drawn:

https://cdswiki.ligo-wa.caltech.edu/wiki/GIMPDrawOvalsAndCircles

We've also talked about seismic watchdogs a bit and why the ISIs trip after the isolation loops are shut off by the guardian. Both ETMs are in damped right now so we set the T240 threshold to 100 counts, and sure enough, the T240s started counting saturations, but did not trip the watchdog. Attached plot shows the T240 saturation counts, threshold and ST1 WD mon state. The dip on the top left plot is where we reduced the threshold, the spike on the bottom left is where the model started counting T240 saturations, and the flat line bottom right shows the watchdog didn't trip. This is as it should be.

However, what I think I've seen during ISI trips before, is the ST1 T240s saturate, ST1 trips and ST2 runs for a little bit then trips. This results in ST1 getting whacked pretty hard. I'll try to see if that's what happened with this earthquake.

J. Kissel, inspired by conversation from S. Cooper, S. Dwyer, J. Warner

I'll remind folks that this collective SEI/ SUS watchdog system has been built up sporadically over ~10 years in fits and spurts as reactionary and quick solutions to various problems by several generations of engineers and scientists. Also, the watchdog system is almost entirely designed only to protect the hardware from a software failure, and never designed to combat this latest suggestion -- protecting the hardware from the earth. So I apologize on behalf of that history at how clunking and confusing things are when discussing what to do in that situation. 

Also, I'll remind people that there are three "areas" of watchdogs: 
    (1) in software, inside the user model -- typically defined by the subsystem experts
    (2) in software, inside the upper level iop model -- typically defined by CDS software group, with input from subsystem experts
    (3) in hardware, either in the AA/AI chassis, or built into the analog coil drivers -- typically defined during initial aLIGO design phase

In my reply here, I'll only be referring to (1) & (2), though I still have an ECR pending approval regarding (3) -- see E1600270 and/or FRS Ticket 6100.

With all that primer done, here's what we should do with the suspension user watchdogs (1), and not necessarily just for earthquakes:
    (a) Remove all connection between SUS and the ISIs user watchdogs. The independent software watchdogs (2) should cover us in any bad scenarios that that connection was designed to protect against.
    (b) Update the RMS system to be *actually* an RMS, and especially, one that we can define a time-constant. The RMS system that is currently installed is some frankenstein brought alive before bugs in the RCG were appreciated (namely LHO aLOG 19658), and before I understood how to use the RCG's RMS function in general. The independent software's watchdog (2) is a good role model for this
    (c) We should rip out all USER MODEL usage of the DACKILL part. The way the DACKILL used across suspension types and platforms with many payloads is confusing and inconsistent. Any originally designed intent of this part is now covered by the independent software watchdog.
    (d) Once (b) is complete, we should tailor the lower the time-constants and the band-passing to better match the digital usage of the stage. For example, the worst that can happen to a PUM stage is getting sent junk ASC and Violin Mode Damping control feedback signals when the IFO has lost lock, but the guardian has not figured it out and switched off control.
    (e part 1) Upon watchdog trip, we should consider leaving the alignment offsets alone. Suddenly turning off alignment offsets often causes just as much of a kick to the system as what had originally set off the watchdog. HEPI has successfully implemented such a system.
    (e part 2) We should re-think the interaction between the remaining USER watchdog system and the Guardian. Currently, after a watchdog trip the guardian state immediately jumps to "TRIPPED" and begins to shut off all outputs and bringing the digital control system to "SAFE." 
    (f) Add a "bypass" feature to the watchdog such that a user can request the "at all costs, continue to try damping to top mass" in the case of earthquakes.

I'm attaching some more plots of what happened to the ISIs during this earthquake. The first plot is the saturation count time series for all seismometers and actuators for the test mass ISIs. All of the chambers saturated on the Stage 2 actuators first, this is the first green spike. This tripped the high gain DC-coupled isolation loops, and probably cause Stage 2 to hit it's lockers. The watchdog stopped counting all saturations for 3 seconds (by design), then immediately tripped damping loops on the saturated L4Cs or T240s. I'm not sure why the GS13s don't show up here.

The second plot I attach shows how long the ETMX was saturating different sensors. The L4Cs were saturated for about 45 seconds, the T240s and GS13s were saturated for minutes. The L4Cs never had their analog gains switched, but the chamber guardian should have switched the GS13s automatically. For this reason, if we increase the pause time in the watchdog (between shutting off the isolation loops and full shutdown), I think this shows that for this earthquake the ride-thru time needs to be more than 45 seconds.

J. Kissel, D. Barker

Description of changes to ISI and OAF top-level models can be found in LHO aLOG 38943.

Final alignment numbers for the new monolithic are below.  All measurements were done with the ITMx suspended, PUM and UIM locked.  All directions assume the reader is looking in the +X direction (i.e. at the ITMx AR surface); it should be noted for future reference (if comparing to the numbers in the alignment notebook) that this is opposite the convention used in the alignment notebook, which is set relative to the IAS equipment used in the alignment and looks in the -X direction (at the ITMx HR surface).

• Roll
  • PUM: 0.15 mm CCW
  • ITMx: 0.20 mm CCW
• Pitch
  • PUM: 1.51 mrad down
  • ITMx: 1.20 mrad down
  • Differential: 310 µrad up
• Fiber Stretch
  • Left: 5.7 mm
  • Right: 5.8 mm
• PUM/ITMx Center of Mass Separation
  • Left: 601.5 mm
  • Right: 601.4 mm

The serial numbers of the fibers used and their locations in the monolithic are as follows:

• +X/+Y
  • SN S1400158
• -X/+Y
  • SN S1400137
• -X/-Y
  • SN S1400164
• +X/-Y
  • SN S1400154

Further discussions on the results presented here has led to realize that the in-air measurements of the violin modes fundamental frequencies have a potential error of about 0.25Hz (as an example here are measurement results for LHO ITMX suspension). In base of this and to better understand the actual differences between in-air and in-vacuum measurements, now that we have very accurate measurements in-vacuum, it would be informative to measure in-air values once the suspensions are taken out. 

The in-air measurements have so far been done by acoustically driving the violin mode resonances. During this measurements the frequency of the driving acoustic signal is changed as a sweep sine. Because the in-air Q of the violin modes is considerably less than the in-vacuum values of 1 billion, if the sweep sine drive is not done with suitable slow pace then the observed a violin mode excitation at a frequency on the sweep sine which actually correspond to a previous frequency of the sweep but took some time to  ring up. Under this assumption, if the sweep sines were driven down (from high frequencies to lower frequencies) then there would be a consistent error on the measured in-air frequencies with values being lower than in-vacuum ones.

A way to improve the acoustic excitation could be by building a tower of speakers so that they could inject more energy into the violin modes of the fibres. Also be sure to drive the sweep sine at enough low pace or inject random noise excitation instead. Finally a lot of information could be gained by in-air measurements of higher order harmonics, this would help on characterization and understanding of higher order inharmonicity as well as higher order mode identification. 

In order to proceed with the in-air measurements of the violin mode and its harmonics during the installation of the suspensions in the near future (as well as measuring the already install suspensions once removed), we have built in Glasgow a line array of 24 speakers of 60 cm length to match the length of the fused silica fibres. Its lightweight and compact design make it suitable to locate it parallel and in close proximity to the fibre that wants to be excited.

This line array produces considerable sound from 300Hz and well above several kHz making it suitable to excite the fundamental mode and up to the 6^th harmonic and beyond.

A more complete description can be found on the technical document T1700414T1700414.

It is relevant to this alog to remember that while preliminary FEA modelling of the actual fibre profiles measured during installation of the LHO ITMX suspension (end of March 2014), has been used to predict in general terms the observed departure of the frequencies of the violin mode harmonics from whole multiples of the fundamental (“inharmonicity”):

However this preliminary results show that this prediction is not yet accurate to the few Hz level required for identification:

In order to complete the list of possible causes for the different inair and invacuum measured violin mode frequencies, I add next the contributions suggested recently by Norna, Dennis and Jon Feicht:

Violin modes frequency variations due to air damping

Air damping lowers the in-air measured violin mode frequency by a value inverse proportional to the violin mode’s Q-factor. Such that the maximum frequency for a damped oscillator (f_m) is related to the undamped maximum frequency (f₀) by:

f_m = f₀ ∙ sqrt[1-1/(2∙Q²)]

A quick look at recent in-air measurement on the LHO alog 38743 suggest a Q of at least 100 in-air at the ~ 500 Hz fundamental mode. This would give a in-air measured frequency value of the fundamental of 0.012Hz lower than in-vacuum.

Violin modes frequency variations due to mass/length of the fibre decreasing as the water desorbs from the silica fibre in vacuum

The mass loading on the fibre, due to water adsorption in-air, should in principle cause the in-air measurement of the violin mode fundamental frequency to be lower than in-vacuum, as once much of the water is pumped off the fibre in vacuum the frequency should increase. Dennis Coyne calculated that about ~3500 monolayers of water (each 2.5 angstroms thick) would be necessary to cause a 1 Hz shift at 500 Hz, due to mass loading alone. It is commonly asserted in vacuum literature that stainless-steel surfaces of a vacuum system exposed to air can start with "hundreds of monolayers of water".

However fused silica is hydrophilic and the interaction of silica surfaces and water is complex; Surfaces of silica under water can swell and form layers of silica gel¹. The modification of the fused silica surface by the chemisorption and physisorption of water may even lead to a reduction in the elastic modulus of the fused silica in the outer layers.

References

[1] V.V. Yaminsky, et. al., "Interaction between Surfaces of Fused Silica in Water", Langmuir 1998, 14, 3223-3235.