I found that the PSL PZT peri mirror LPF (D1500001) uses 220 Ohm resistors in line with PZTs, each axis having 6uF capacitance. That gives the pole of 120 Hz, which is too high.

It turns out that LLO uses 220 kOhm, which is a bit too big.

After consulting with Peter Fritschel I decided to use 22kOhm, which gives us 1.2Hz pole.

Filiberto fitted the spare (S1500002) with 22kOhm resistors. I and Sheila went in the PSL room and swapped the old one (S1500001) with the spare.

Before the swap we checked the beam position outside of the PSL room, which was maybe 1mm lower than the marks.

After the swap the beam position didn't change and MC locked without problem.

Since IMC WFS DOF5Y loop was NOT doing anything useful these days (as the noise spectrum shape changed), and since I need to measure the TF again if we want to enable this loop, I turned off the output of the loop.

This is the new configuration for now.