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AdV-SAT (Suspension control upgrade)
Paoletti, Sposito - 17:45 Friday 22 February 2019 (44973) Print this report
Modification on NI and WI Coils cabling/connection
Today we have changed the way the input towers coils are left in LN3 when no more in use.

Up to now they were still connected to the Coil-Driver boards via a high value (2 x 100k = 200k) resistor, in order not to reintroduce the P5 board noise.
The side effect was that a possible "common mode noise" acting on a charged mirror would enter as it is, having the resistors no effect on it.
On the other hand we can't left the coils unplugged (simply opening the relay) because we know the wires act as an "antenna" for the 50Hz mains.

Today: we removed (cutting one side only) the high value resistors that were left in parallel to the opening relay, and we added (yet some other) IN/OUT boxes where the Coils are plugged and the signal is simply connected to the relay box, having inside two low value resistors (1k) connected to the vacuum chamber of the tower (call it GROUND).
That way the Coils are REALLY unplugged when in LN3, and at the same time they are not left floating.

All this work, beyond being a good practice, is needed for the upcoming test of the "active common mode noise subtractor" that should be put in operation next week at the END mirrors, that can't worl properly if in the FP arms the Input mirrors are reinjecting common noise (the reduction could be no more than sqrt2)
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Comments to this report:
bersanetti - 18:10 Friday 22 February 2019 (44975) Print this report

The adaptive feed-forward for the 50 Hz line has been switched off (just in case) by sending 0 to the WI DSP; the old sensing is left commented in the Automation.

Paoletti, Passuello, Magazzu', Nocera - 16:21 Wednesday 20 March 2019 (45330) Print this report

The test (active common mode noise subtractor) has been done this morning, but had no visible effect in 50Hz and 150Hz lines.

We have then decided to roll-back everything (END mirrors as well INPUT mirrors); now the situation is the same as before Feb 22nd (see entry 44973)

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