Dither line

With lownoise_ASC back to a stable state, we had a chance to move another of the dither lines back to the 20Hz region (carrying on from last month). I moved PIT5, which controls the spot position on ETMY, back from 6.9 Hz to 20.789 Hz, and saw an improvement in DARM (first attachment). Still unclear why there is such a dependence on the dither line frequency. Second attachment is the time series of PIT4 (X arm) and PIT5 (Y arm) converging (in the case of PIT4 very very slowly) after I move the line. Bottom row is test mass op levs.

I reverted the settings in the guardian however tomorrow commissioners might want to pay attention in ENGAGE_SOFT_LOOPS and LOWNOISE_ASC and add extra gain if things are taking too long to converge.

180 Hz and OMC PZT3 out

With the new OMC PZT driver we've had a problem with a broad 180 Hz peak in DARM (third attachment shows a high-ish resolution spectrum taken between references). Currently while locking, the high voltage driver is sending a 10 V offset to PZT1 which is used to dither the length of the OMC. On Rich's suggestion I tried slowly adding an offset to this PZT (PZT3 in the OMC control screen), allowing the length change to be offloaded onto PZT2, and looked to see if the 180Hz peak changed. I got to 0V on PZT3, and saw no change in the 180 Hz noise.

Soft loop engagement

While acquiring lock earlier today we got stuck in engage_soft_loops. In the guardian we first turn on PIT3 and YAW3 which control the PRM pointing, and only engage the other loops once they're within a certain range, at one point today PIT4 (Xarm pitch) was not within that range. I used Hang's handy arm-slider-moving script to move the X soft P degree of freedom until it the dither error signal was close enough to be turned on. If this becomes a recurring problem we might need to loosen the convergence checker in guardian.