jim.warner@LIGO.ORG - posted 17:58, Monday 10 August 2026 - last comment - 12:08, Tuesday 18 August 2026(91468)
Testing high voltage CPS on HAM8 ISI overnight
While Huyen is here, we've dug out the high voltage CPS that we got several years ago to try testing them on HAM8 again. We have a little preliminary data, that doesn't look good so far, but we will try to see if we can get any improvements over the next couple of days, while HAM8 is still isolated from the rest of the detector.
We had the HV CPS connected at HAM8 ISI from Monday 08/10 to Friday 08/14. We could not get the HV CPS noise floor (around 100Hz) down to expected level - x4 better than the normal CPS sensor noise as seen before in alog 78287 (tested at HAM7). Figure 1 is HV CPS noise at HAM8 - reference is th normal CPS before swapping. As we troubleshooted, the noise got modulated some but never get to expected noise floor. The best we can get is x2 better. Another issue is that some HV CPS noise floor is not stable, see short figure 2 and clip #1.
We have tried to troubleshooting this without success by isolating all the rack and interface/ethernet boxes off the ground, adding some wrap to make them more thermal stable, swapping cables around. From the start, the light indicators on the board did not make sense. While plugin, the near/far light on H2 module never went away, and the light on H1 and H3 modules were not even on even before plugging in. However, the signals looks okay in timeseries. The ISI can still be isolated with these HV modules.
I've tried to select the time where few of the noises is low and best present cartisian DOF to check the performance, but none looks great.
If the noise is not stable and comparable between sensors, this is hard to tell if the performance improved or whether the HV CPS actually helps.