On Fri, 11 Sep 2009 10:00:30 -0400 Brett Nordgren  
wrote:

> Hi All,
> 
> A few days ago, Dave Nelson in California was able to obtain the loan of a 
> Nanometrics Trillium Compact-120, a professional quality triaxial packed 
> into a can only slightly larger than a large geophone.  Our plan is to 
> compare its output with the home-built Force Balance Vertical running 
> beside it.
> 
> Soon after it was installed, California obliged with a nice 3.9 up the 
> coast which gave us a modest sized test signal containing some higher 
> frequency energy, which we could use to compare the two instruments.  Both 
> instruments' outputs were filtered with a 20Hz 4-pole low pass and the 
> Trillium had a two pole high-pass added at 1/50Hz, in order to match the 
> 50-second low frequency rolloff of the FBV, since its own rolloff was at 
> 120 seconds.
> 
> The results are shown at http://bnordgren.org/seismo/TvsFBV01.gif  or the 
> somewhat larger  http://bnordgren.org/seismo/TvsFBV01.jpg
> 
> Question:  Which is the $7000 Trillium and which is the FBV built by Dave?
> 
> Regards,
> Brett .

You have checked that you haven't connected both channels to the same sensor? :)



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