Jennie W, Sheila D

Summary: tried to use ETMX injection to tag light coming from the arms at the REFL port as we step the darm offset, didn't get a full measurement as we lost lock - seems unrelated.

During the commissioning period and while Robert as doing shaker i jections, I tuned a line at 74.37 Hz on the SUS-ETMX_L3_CAL_EXC. This is the same point at which the ETMX CAL line input goes in (where the calibration exc for ETMX is injected into the DRIVEALIGN matrix). The psds shown were measured about a minute before lost lock and it can be seen that the rms motion in the upper left of the ETMX bottom mass is not reaching its limit.

The settings I used in AWG are shown in this photo.

After checking the height of the line in DARM, OMC REFL and the rms on the upper left ESD readout, I tried to take a darm offsert step measurement using autodarmpoffsetstep.py (using the ETMX line instead of the PCAL lines to readout the optical gain). To do this I comment out the setup_pcal_for_darm_offset_step and restore_pcal functions in autodarmoffsetstep.py before running it.

I had to the stop the measurement twice to trurn off the OMC ASC and put the X0 offset back to what it was before the measurement. One step into this measurement set we then lost lock (around 2 minutes into the final attempted DARM offset measurement). We can't see any evidence so far as this was the causer of lockloss as the line had been running for 40 minutes or so without breaking the lock.

Data is saved in an xml in /ligo/gitcommon/jennifer.wright/git/DARM_OFFSET