I performed the shaker injection tests for the OMC base plate, by locating a 3-axial accelerometer (TEAC710Z) on the optical table and a 1-axial accelerometer (TEAC710, for vertical) on the base plate.
I calculated the transfer functions from the base vibration (z) to the table vibration (x,y,z).
Comparing the results of hammering (klog29515), inconsistency is found.
The underestimation below 70Hz is solved.
Note that the TFx and TFy are the vertical -> horizontal coupling in this shaking test, but were the horizontal -> horizontal coupling in the previous hammering test. So their comparison is not fair.
I performed a follow-up study to check whether the acoustic coupling was serious or not.
I located a microphone inside the chamber without touching the chamber, table, base, and stacks.
In this study, a coupling function (CF) is evaluated instead of a transfer function to avoid the effect of the background noise.
The evaluated CFs are
- The base acceleration to the table acceleration via shaker injection
- The base acceleration to the sound via shaker injection
- The sound to the table accelration via acoustic injection injection
and finally, 2.* 3. is the CF for the base acceleration -> sound -> the table acceleration.
The results shows
- the shaker can generate enough larger vibration than the background.
- the sound induced by the shaking was very small and smaller than the background for the most frequencies.
- contribution of the acoustic coupling in the Base -> Table vibration path.
