Oli, Elenna

The DC1 and DC2 centering loops have seemed to be way too slow, so Oli and I took some transfer functions of the centering loops. We started with DC2 Y, and the loop didn't even seem to have a UGF. By looking at the phase, Oli and I determined that we could raise the loop gain to get a UGF of about 0.5 Hz with a phase margin of 38 degrees. This involved raising the gain from -0.1 to -8.

The DC1 and 2 yaw loops have the same design and feedback to the same suspensions, so we copied over the gain change and ran a quick OLG to confirm the result is the same.

DC1 and DC2 pitch also have the same design. The low pass filter in use in pitch cuts off at 0.7 Hz instead of 1.5 Hz like the yaw loops, so there was much less phase margin. Oli and I copied over the butterworth low pass at 1.5 Hz in the yaw loops to the pitch loops and found that raising the gain from -0.1 to -7 gave the desired 0.5 Hz UGF.

All four loops have been measured using the templates in [userapps]/asc/h1/templates/DC_centering and saved. I have attached screenshots of DC2 Y and DC1 P. We SDFed these changes.

We copied over the DC1/2 design to DC6 yesterday, so Oli and I also updated the low pass filter in DC6 P to match and SDFed. The gain of DC6 P and Y still needs to be checked.

As a final note, we lowered the bandwidth of these loops just before O4 to avoid noise reinjection into CHARD, so we should check how this higher bandwidth impacts the noise in CHARD at a later date.