Problem

We started checking the health of QPDs and were puzzled that all four quadrants of the OMCA QPDA are much, much noisier than OMCA QPDB.

Note, there's a naming inconsistency about the QPD numbering between D2200276 wiring diagram and D0981811 (see "cartoon version"). 

Cause of the problem

Anyway, the problem was tracked down to short-circuit of common mode noise sensing line for OMCA-QPD1 (pin 11 of DB25 inside the vacuum, pin 3 outside of the vacuum, see attached) to the metal part of the suspension structure (i.e. ISI surface and the chamber) which in turn is grounded to the lab ground.

OMCA QPD-2 as well as both of the QPDs for OMCB are fine.

All QPD segments (incl. OMCA QPD1) responded to the flashlight.

Dark noise test: OMCB QPDs looks OK, not sure about OMCA QPDs

We connected a dual-QPD trans impedance chassis (S1102832, which is the original version of D1002481) to the OMCB QPDs like this:

QPDs-DB25 assy - in-vac cable (DB25F-DB25F)  - feedthrough simulator - DB25F-to-DB25M-cable - S1102832 front panel.

We looked at the output of the TIA with SR785 when there's only ambient light on QPDs (not much), segment by segment. No segment was extra noisy or anything.

OMCA QPDs are a different story because of the 60Hz problem. 

We'll see if the problem could be solved by somehow reassembling the QPD or cutting the noise line. 

Cabling to the ISCT1 and JAC table enclosures complete. Use caution when moving the cleanroom, one of the legs is close to the patch panel/cables on ISCT1.

TITLE: 04/27 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY: The BSC2 cartridge has been flown over to the test stand in the West bay.
LOG:

FAMIS 31135

The PSL was offline for a bit last Tuesday for chassis work that took down the interlock (alog89965), but came back up with only a few things being different. Most notably, the PMC is at a slightly different temperature, so the transmitted power is a bit lower while the reflected power is a bit higher.

The BSC2 cartridge was removed from the BSC2 chamber today and placed on the Test Stand in the West Bay (+Y bay).  The lift took 3 "test lifts" to make very minor adjustments to the CG prior to lift out of the chamber - on the 4th lift, we were very well balanced so embarked on the flight.
Like LLO, the BS had it's "Stay Leg" assemblies and Vibration Absorber Assemblies removed for the flight.  This means it was probably lighter than the 2013 time (alog 5689) when we did this which had the weight slightly heavier.  The cartridge plus 3-point lift fixture and load cell together all weighed 9380 lbs.  It was rotated 90deg Counterclockwise per the procedures and landed on the threaded rod in the test stand with little issue other than careful craning and spotting.
All went as expected and according to the procedures E1200433-v3, E1200971-v4 and associated docs.

Mitchell, Travis, Tyler, Randy (on crane) all up on the platform
Jim and Tony inside of BSC2
Gerardo, Jordan on the eMod as Support
TJ on the camera
Betsy soaking it all in (support)

A pre-lift meeting was held to go over the teams and maneuver details (again) at 9am prior to work starting.

Particle counts up at the dome level were all 0,0 before starting.
More photos and videos will be posted when those folks have them available.

Covers used - A BS/QUAD SUS tube cover up underneath, an ISI cover up on the ISI, the BSC Cartridge sock which encased the whole thing, dropped down to Jim and Tony once the lift was up a couple feet.  

The bulk of the work was from ~10:30am-1pm.  Most of the time before was getting folks in headsets and gear and getting equipment on.

As of 20:05 UTC, the cartridge from BSC2 (including the soon-to-be-decommissioned beamsplitter) has been placed on the test stand in the LVEA West bay. The cartridge was first lifted at 19:15 UTC before making its slow procession across the LVEA via the 5-ton overhead crane. More details and documentation to be posted later.

I've been trying to understand how to make estimates of actuation strength for thermal actuators, and I wanted to make a summary to make this easier in the future.  With .  

In looking at data from the HWS, the values are divided by 2 to account for double passing (the compensation plates, ITM substrate, and SR3 are all double passed by the HWS beam).  These are then reported in micro diopters of spherical power, which is a measure of the change in wavefront curvature. 

If we are using these values to calculate the focal length of a lens, we would use:  f_new = 1/(1/f_original +spherical power)

If we are talking about a curved mirror, and we want to calculate the radius of curvature we use:  Rc_new = 2/(2/Rc_original + spherical power)   

Mon Apr 27 10:07:42 2026 INFO: Fill completed in 7min 39secs

TITLE: 04/27 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: MAINTENANCE
    Wind: 9mph Gusts, 5mph 3min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.16 μm/s 
QUICK SUMMARY: The BSC2 (BS) cartridge is planned to be flown out of the chamber and onto the test stand in the LVEA West bay today!

Friaday Jim and I installed the lifting pads onto BSC2. Jim also secured disconnected cables, while I assisted Ibrahim with suspension gusset removal.

Sun Apr 26 10:08:57 2026 INFO: Fill completed in 8min 54secs

Sat Apr 25 10:09:51 2026 INFO: Fill completed in 9min 48secs

Fri Apr 24 10:11:05 2026 INFO: Fill completed in 11min 1secs

TITLE: 04/24 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:

CDS Frame Write restarts @ 15:21 UTC

Lots BSC2 work was done today.
Beam splitter Stays were removed and in between BSC2 and HAM4. Pictures of the Beam Splitter cover and more details can be found here: alog link. 
The Beam splitter cartridge is closer than ever to fly out of the BSC2 Chamber. 

LOG:

Ibrahim, Jim, Mitchell

Mitchell and I removed the BS stays from the beamsplitter and placed them in the tube between BSC2 and HAM4. Then, Mitchell and I put the cover over the BS.

Jim and Mitchell were working on removing and bundling SEI cables from inside BSC2 for storage by ISI. Jim (on ISI) and I (in BSC2) then removed cable clamps from the bottom of the ISI/ceiling of BSC2.

Picture provided.

J. Kissel

After the install of front-end software (LHO:89777 and LHO:89919) the next step for SPI is MEDM screens -- the UI/UX for the SPI L interferometers and PY one-way optical levers.

Here, I post screenshots and corresponding userapps svn file and location.
Sub-screens and their future purpose will come in the comments, but make sure to also check out G2402138.

In the main entry, I show off the new place that SPI lives on the LHO sitemap and the overview screen.
The overview screen, and all subordinate screens use a marco file, which I also attach.

All of these files are, of course, properly version controlled in the userapps SVN, here:
OVERVIEW SCREEN
    ${USERAPPS}/spi/common/medm/
        SPI_CUST_OVERVIEW.adl        rev 35102

MACRO FILE
    ${USERAPPS}/spi/h1/medm/
        h1spih23_overview_macro.txt  rev 35106