Ibrahim, Rahul

Attached below are the B&K (Bruel & Kjaer) measurement results of A+ HRTS (suspended config.) mounted on BBSS structure - see picture over here. We used a tri-axis accelerometer mounted on the BBSS frame as shown in this zoomed-in picture - X axis is along the longitudinal side of the BBSS, Y axis is the vertical and Z is transverse.

At first we measured BBSS alone (without mounting the HRTS) - see results posted here. Using a hammer (force transducer attached to a front end - recording the hammer and accelerometer data on the B&K software) we hit BBSS structure in X, Y and Z direction (of the accelerometer). The hit was hard enough to not cause a soft hit, while taking care its not saturating the sensors. We see a small spike at around 68Hz on X axis hit, which is similar to what Jim saw in his measurements few months ago - LHO alog 79930. However, at that time BBSS was without its side braces for providing structural rigidity.

The second plot represents BBSS with HRTS mounted on it. Here as well we see some peaks below and around 70Hz.

Both the suspensions were unlocked and suspended during this measurement.

I am processing and analyzing some additional data (taken for sanity check) by moving the accelerometer to a different location on the BBSS, and will be posting those numbers soon.