Corey, Eric, Greg, Jim, Mitch, Vincent, Hugo

Unusual resonances were observed above 100Hz on LHO HAM-ISI Unit#1.  GS13 doors and their brackets were not fully bolted and torqued. These mistakes were corrected, however, the resonances observed only disappeared when Viton pads were added under the ISI‘s Top Mass. 

It is possible that the top mass had uneven contact with the optical table causing it to rattle (We could actually hear the mass ring when being hit with an allen key).  

However, we want to make sure that the resonances are not reduced by the couple "Viton+Top mass" behaving as a mass damper. We are currently trying to find out by measuring the ISI's response with its top mass sitting on a kinematic mounting. 

The comparison curves of the TF before, and after, adding Viton pads under the top mass of the ISI are attached.


Note: The picture of the top mass was taken a bit more than a week ago. The balancing masses layout is not as on the picture anymore, but the top mass remained roughly at the same position (slightly re-centered during Viton Pads insertion).