J. Kissel, T. MacDonald

We've finally collected our "money" data set on ETMX HEPI/Chamber system -- and a quick look at the mode shape at 8 [Hz] reveals that this motion is the two crossbeams moving in concert along the beam direction (see ETMX_HPI_8Hz.avi). However, contrary to popular belief, this mode does *not* really involve the piers, the slab, or the chamber. 

Excited by the result (no pun intended), and having a measurement method and system nailed down, we packed up and high-tailed it to ETMY. We took the identical measurement there, and got the same exact mode shape (see ETMY_HPI_8Hz.avi). So it's systematic to the HPI/Crossbeam system, as has been indicated by the good Dr. Nuttall's work (see, e.g. G1400858). You'll notice that three data points on the cross-beam in the distance are exactly out of phase with everything else -- this is a measurement artifact: due to access issues (the chamber work platform is still set up at EY), so I had to hit that cross-beam from the opposite site (we're looking into whether we can somehow just invert the phase of those few data points with the B&K software).

This settles the argument as to what I've moving at 8 [Hz] here at the sites!

Now that we've got the result we want, and a whole lot more data to work with (we have modal information with 0.5 [Hz] resolution up to hundreds of [Hz]), we're going to use the one day two days that Tim has left to take finer resolution data on the horizontal cross beam / pier top / HPI boot system to nail down the exact mode shape so we can consider ways to *fix* it.

(Again there's too much data to export at the moment, and this can easily be done offline -- which Tim will do back at Stanford, but stay tuned for more fun results!)