A few weeks ago, we discovered we had a FAILED Horizontal GS13.  From our quick tests, it seemed as though we had a stuck mass inside the GS13---we were able to free the mass when we tilted the Table.

For an exercise in checking the effects of a tilted table on our remaining functioning GS13s, we carried out some table tilt measurements on the table and looked at spectra from our GS13s (namely the Horizontal ones).

We tilted the table by placing weights on the table in various locations.  We used various types of Adjustment Masses D071200.  Here are masses for the types of weights we used to tilt the table:

Type 1:  0.5 kg
Type 2:  1.0 kg
Type 3:  2.1 kg

As for the tilts, we did a few.  Referencing this coordinate drawing(sorry, for some reason, aLOG wouldn't let me upload this picture), we tilted the table along several axis:

RY:  +RY tilt would have weights placed over the V1 GS13 (-RY had weights on side opposite of V1 Act).  The RY tilts would tilt the H3 GS13 up and down along its axis (which is parallel to X

RX:  +RX tilt would have masses placed over H3 GS13 (-RX would have masses placed on side opposite H3 GS13).  This measurement doesn't really line up with a clean tilt for any of the horizontal GS13's; they are all at angles with respect to RX tilts

"H1":  Here we wanted to perform a tilt for the H1 GS13 (similar to what the RY tilt did 
for the H3 GS13).  A "-H1" tilt had masses placed over the V2 GS13 ("+H1" tilt had masses on spot opposite to V2 GS13.

"H2":  Here we wanted to perform a tilt for the H2 GS13 (similar to what the RY tilt did for the H3 GS13).  A "-H2" tilt had masses placed over the V3 GS13 ("+H2" tilt had masses on spot opposite to V3 GS13.

On this coordinate drawing referenced above,  +Y & +X are the same as H1's (i.e. +Y points toward Rattlesnake Mountain).

Overall, in the measurements we start out with an unlocked & balanced table with it's respective spectra.  Small amount of masses are added (they are posted in each plots title).  The system is ok with a little tilt, but once you get to a certain tilt the spectra changes noticeably (i.e. the primary resonances around 1-2Hz get knocked down & the high frequency behavior changes).

The data for these measurements are saved at:
/opt/svncommon/seisvn/seismic/HAM-ISI/X1/Data/unit_1/dtt
With file names:
20100713_+RXtilt_geo_spectra.xml
20100713_-RXtilt_geo_spectra.xml
20100713_+RYtilt_geo_spectra.xml
20100713_-RYtilt_geo_spectra.xml
20100713_+H1tilt_geo_spectra.xml
20100713_-H1tilt_geo_spectra.xml
20100713_+H2tilt_geo_spectra.xml
20100713_-H2tilt_geo_spectra.xml