arnaud.pele@LIGO.ORG - posted 20:34, Thursday 08 May 2014 - last comment - 19:30, Thursday 15 May 2014(11786)
SR2 lower stages TF
Yesterday night, I tried to run SR2 M2-M2 and M3-M3 (lower stages) in chamber transfer functions after the osems were centered on wednesday. Although both M2 and M3 watchdogs tripped during the measurement, so I am running it again tonight. (This time, I decreased the drive and increased the watchdog threshold).
Decreasing the drive didn't help either since I ended up with measurements without coherence. This morning I tried to drive M2 stage with high amplitude sinewaves at the resonant frequencies of the suspension for each DOF (L P and Y) to see if the osems would saturate. They don't. So a drive of 500 000 (cts) for L and 20 000 (cts) for P and Y (which is the limit before saturating the DAC) should be optimum at all frequencies. Started a new measurement which will run today.
This time, phase 3a M2-M2 and M3-M3 measurements of SR2, in air, with the HAM-ISI locked were succesful. The actuation is functioning, and the transfer functions for the three degrees of freedom are similar to the model.
There is one interesting feature to note for M2 stage. From 10Hz, the measured tf rolls up, as if some extra zeros were added to the tf. I checked the osem output filters, and they seem to compensate correctly for the coil driver (looking at the state diagram in state 1).
Attached are some SR2 phase 3a spectra for future reference