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Entry  Thu Nov 10 19:41:24 2011, Jenne, Update, SUS, Musings on SUS dewhitening, and MC ELP28's 
    Reply  Fri Nov 11 13:26:24 2011, jamie, Update, SUS, Musings on SUS dewhitening, and MC ELP28's 
Message ID: 5865     Entry time: Thu Nov 10 19:41:24 2011     Reply to this: 5873
Author: Jenne 
Type: Update 
Category: SUS 
Subject: Musings on SUS dewhitening, and MC ELP28's 

The following will be a stream-of-consciousness, approximately chronological story of my last hour or so of looking at screens....

In the old OAF days, we used to bypass the analog dewhitening in the coil driver path, using the XYCOMS.  See, ex. elog 2548.

I began to wonder if we needed to do the same thing now.  I checked several optics, to see how the switching works. 

For the whitening on the OSEM sensor input, FM1 is linked to the Contec binary I/O.  FM1 is the inverse whitening filter.  Turn it on, and the analog whitening is on (bit in the binary I/O screen turns red).  Turn it off, and the analog whitening is bypassed (bit in the binary I/O screen turns gray).  Good.  Makes sense.  Either way, the net transfer function is flat.

The dewhitening is not so simple.  In FM9 of the Coil Output filter bank, we have "SimDW", and in FM10, we have "InvDW".  Clicking SimDW on makes the bit in the binary I/O screen gray (off?), while clicking it off makes it red (on?).  Clicking InvDW does nothing to the I/O bits.  So.  I think that for dewhitening, the InvDW is always supposed to be on, and you either have Simulated DW, or analog DW enabled, so that either way your transfer function is flat.  Fine.  I don't know why we don't just tie the analog to the InvDW filter module, and delete the SimDW, but I'm sure there's a reason.

All optics have this setup, except MC1 and MC3.  They don't have the SimDW or InvDW filter modules.  Instead, in FM9 (which on all the other suspensions is SimDW, and controls the binary I/O) there is a 28Hz Elliptic Low Pass filter.  The only thing I can find about these is elog 1405 where Rana talks about implementing ELP28's in MC2.  But right now there is no ELP in the MC2 coil output filters.  So, if Rana's old elog is to be believed, we need to fix up the ELP28 situation.  But that elog was from a long time ago, so maybe things are different now?  If MC1 and MC3 need the SimDW and InvDW (why wouldn't they?) then the ELP28 needs to move to another filter module.  Because right now, when I click the ELP28's on and off, it changes bits in the binary I/O.  Which I don't think it should.  Maybe.  I don't really know.

Okay. So. Now we know where everything is, and which buttons do what.  Maybe not why, but at least what.

In the old world, Rob had lots and lots of trouble (elog 2027) with locking when the analog dewhitening was bypassed.  But right now, I think that all of the analog dewhitening filters are bypassed, for every single optic we have.  So.  Which way do we want things?  What's the new game plan.  What's going on??


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