J. Kissel, S. Dwyer, E. Hall As I was about to characterizing the ETMY coil drivers (i.e. the UIM and PUM), I noticed that they were in their highest noise state. After conversations with Sheila and Evan, we (re)agreed that the PUMs should be run in their lowest noise state, which is with LP ON and ACQ OFF, or State 3 from T1100507. As such, we've switched all QUADs to this state, and confirmed that ISC_LOCK guardian will ensure this to be true in the future (again). That guardian has been reloaded. The reason they had been put back into high range (and taken out of the guardian) was that the range was needed to better damp the QUAD roll modes after they had been severely rung up in the Christmas Episode in early August. From a calibration stand point, this will affect the DARM calibration by a small amount, but I had not started characterizing the ETMY PUM drivers before I got started, and I'm now full aware of it, so it's affect will be fully understood and expected. As such, we're OK with this configuration change. Further, we'll all be happy with the little bit extra range we get from it (Evan will post an aLOG making a noise statement later)!
We can hear saturations on the quads during CARM offset reduction and when powering up, but I suppose that's the price we pay for the improved noise performance. [See attachment—blue is from yesterday (coils in high-range), red is from today (coils low range). I can't really claim that the improvements at 70+ Hz are from the coil switching, though.]
We would like to acquire with high range and then switch to low noise at some point during the lock, but the transients unlock the interferometer most of the time. Jeff suggests that we commission the digital switching delays. Perhaps that can be done parasitically with calibration activities.