Filiberto, Peter, Rich

The analysis of the OMC grounding and shielding is complete as far as it can be diagnosed with HAM6 closed.  There is only one area associated with the OMC PZT cable that needs to be scrutinized but it is inside the vacuum system.  The attached PDF has been carefully boiled down to the simplest form possible to explain the current situation.

The highlights are:
1.  A 25 pin breakout board was added to the QPD cable to break a ground loop that became apparent during this analysis.  There has been no observable benefit to this change, so at some point it might be that it is removed and the system restored to normal.
2.  The shield of the PZT cable is grounded in the vacuum system somewhere.  This does not create a ground loop per se (see attached diagram to see why), but it's not deliberate, and should be investigated next time HAM6 is open.
3.  There is a break somewhere in the shield of the PZT cable inside the vacuum system.  We don't know how big this gap in shielding is, but it does exist.  This needs to be identified next chamber opening.

I will alert Betsy to the need for these investigations to be added to the "when vent" category of tasks associated with HAM6