Corey, Keita
We were able to get rid of a ground loop on the "solo" QPD by simply moving/touching it's Seismically Responsible Cable.
Moved to Tip Tilts and discovered that two of the three Tip Tilts had grounding loops to the table. After much investigation, Keita appeared to discover the issue. It's related to the BOSEMS and how the connector is close to the aluminum mounting plate which holds them. He was able to do some "surgery" to move the connectors in a way such that they didn't short to this plate. One Tip Tilt (OM3) was repaired, re-installed, and tested good. OM2 still needs to be fixed.
There were three runs of cables (the two WFS cables which run to Flange D3 & the OM2 cable) which were run "under" Stage1. According to Hugh, this is a no-no, so these cables re-run and routed around the perimeter of Stage0.
Believe Keita still had more ground loop issues on his list, and he also wanted to look at the capacitance of the OMC PZT.
In Corey's picture, one unit is fixed, the other is not. You cannot tell which is which if you don't know where to look.
There are two places where the metal connector shell potentially can touch the base plate of the coil, i.e. side and bottom (see the first attachment). There's always a continuity from the coil base plate to the TT BOSEM plate to the TT body to the ISI table, so this is not cool.
The side gap can be made as large as maybe 0.3-0.4mm, or as small as zero, by how you assemble it.
My "fix" was to maximize the side gap. The bottom gap looks incredibly small when this is done, probably 0.1mm or less, but this worked consistently for four coil/connector assemblies that I have re-done.
There is zero reason that these gaps should be this small, by the way. Probably it's too late, but if I redesign it I'll make it like the second attachment.
We'll continue tomorrow.
