thomas.shaffer@LIGO.ORG - posted 09:58, Sunday 11 October 2015 - last comment - 10:47, Sunday 11 October 2015(22410)
More on the 45mHz blend change
Jim W. suggestd that we try out the 45mHz blends if we can't lock due to the high microseism. Just before I came on shift, Travis and Sheila switched them over for the X and Y directions on BS, ETMY, EMTX, ITMY, and ITMX. They decided to do this because of the low winds and high microseism. This seemed to have helped us out quite a bit. Before the change, they struggled getting to lock DRMI, with them switched it only took us a few tries before we were all the way to Nominal Low Noise.
I will be accepting these blend changes in the SDF so we can move into Observing.
Furture operators should change them back if the winds pick up (Sheila says anything above 20 might be too high for these blends), but keep in mind this may drop lock.
For future reference the wind had not gusted above 15 mph for about an hour or so before Travis and I changed the blends, and the microseism is at about 0.5 um/sec in the 100-300mHZ BLRMS now. Before we changed the blends, ITMX optical lever saw about 0.5 urad peak to peak motion, and single arms were not even locking. (ETMX was not moving as much as the ITM) Changing the blends reduced the motion to more like 0.1 urad or even less.
Here are SDF shots so operators know what to bring it back to.
Unfortunately you won't be able to use the SDF system to revert these filters. If you do that you will likely trip the ISI, violently, and it will take longer to recover. You will have open the ST1 BLENDS screen for each ISI and select the appropriate blend from there.