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Entry  Thu Dec 20 12:14:19 2012, Jamie, Update, General, problem with in-vac wiring for TTs 
    Reply  Thu Dec 20 17:13:56 2012, Jamie, Update, General, how to deal with problem with in-vac wiring for TTs 
       Reply  Thu Dec 20 18:33:52 2012, Jamie, Update, General, in-vac adapter cables for TTs invac-adapter-cable.pdf
          Reply  Fri Dec 21 09:55:23 2012, Steve, Update, General, in-vac adapter cables for TTs extensioncable.pdfgenderchanger.pdf
Message ID: 7864     Entry time: Thu Dec 20 17:13:56 2012     In reply to: 7863     Reply to this: 7865
Author: Jamie 
Type: Update 
Category: General 
Subject: how to deal with problem with in-vac wiring for TTs 

So this is obviously a general problem for all the TTs.  Our in-vacuum wiring is unfortunately mirrored relative to that of aLIGO, or at least:

  • aLIGO: in-vacuum pin 1 tied to shield (T1200131)
  • 40m: in vacuum pin 13 tied to shield

And again, the problem is that pin 13 on the TT quadrapus cables is the one of the coil pins for one of the OSEMs.

I think the right solution is to make mirroring adapter cables for the TTs.  Modifying the pins on the stack-top brackets for just the TTs would leave us with a bunch of brackets that are different than all the rest, which I think is a bad idea.  Therefore we leave all the feed-thru-->bracket wiring the same, and make adapters.  I'll describe the adapters in a follow-up post.

The silver lining to this whole thing, if there is one, is that I wired the polarity on the out-of-vac adapter cable at the coil driver in such a way that the drive/send signal went to the grounded in-vac pin.  If I had by chance wired the polarity oppositely everything would probably have worked, except that the return for one of the coils would have gone through the cable shield and the chamber, rather than the return pin to the coil driver.  I'll let you image the problems that would have caused.

Making new adapters will take a little while, but I think we can proceed with the installation and alignment with a temporary setup in the mean time by taking advantage of the polarity I mention above.  We can temporarily swap the polarity so that we can drive current to the coil using pin 13.  This will allow us to complete the installation and do all the alignment.  Once the in-vac adapter cable arrives, we just put it in, fix the out-of-vac polarity, check that everything works as expected, and button up.

We'll pick up all this when we're back on Jan 7.  Steve will put in an order for the in-vac adapter cables ASAP.

I take full responsibility for this fuck up.  We've been unable to find any in-vac wiring diagrams, but I should have checked all of the wiring during the last vent so that we could have prepared for this ahead of time.  Sorry.

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