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Entry  Fri Jun 10 20:23:56 2011, Larisa Thorne, Update, Electronics, Seismometer Box Update/graphs SeisNoiseGraphs.jpg
    Reply  Mon Jun 13 16:27:10 2011, Jenne, Update, Electronics, Seismometer Box Update/graphs NewSeisBoxNoise.png
Message ID: 4810     Entry time: Mon Jun 13 16:27:10 2011     In reply to: 4807
Author: Jenne 
Type: Update 
Category: Electronics 
Subject: Seismometer Box Update/graphs 

Quote from elog 4807:

The noise graphs relating total noise of the Seismometer circuit (GURALP stuff) to the LIGO seismic noise curve have been completed started.

 What Larisa meant to post (I'm sure) is something more like this (sorry it's a little squished...I put too many words in the legend):

I've only included the 2 noise contributions from the LISO model that seem to dominate the sum noise.  The plot gets a little crazy if you include all of the non-important sources.

NewSeisBoxNoise.png

So, what's the point??

First, the new box design doesn't have any crazy-special op-amps in it, so the noise of the new box is probably comparable to the old box.  So, if that's true, the old box may not have been limiting the differential seismic noise.  This definitely needs to be checked out.  I'll make a quickie LISO model of the old Guralp breakout box, to see what its noise actually looks like, according to LISO.  If it wasn't ever the breakout box that was limiting us, what the heck was it??

Second, the current box design seems to be better than the Guralp Spec sheet noise by ~a factor of 10.  It would be nice if that number were more like a factor of 100.  Or at least 30.  So some work needs to be done to find a lower-noise op amp for the voltage buffer (the first op amp in the circuit).

Next steps:

Since Larisa is now starting her SURF project with Tara and Mingyuan, I'll look into improving the design of this box by a factor of 3 or 10. 

Then I'll need to make a mock-up of it, and test it out. 

If successful, then I'll draw it up in Altium and have it made.  Recall that there should be 2 outputs per seismometer channel, one with high gain, one with low gain.  Then 3 seismometer channels per seismometer (X, Y, Z), and perhaps multiple seismometer inputs per box.  So lots and lots of stuff all in the same box.  It's going to be pretty cool.

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