In this alog, I showed a plot that compares the CHARD P and INP1 P noise before and after the HAM1 ISI install. Last night, I took the measured CHARD P coupling function and calculated the CHARD P contribution to DARM just before the vent to install the HAM1 ISI, and from a high range time this past weekend, with the HAM1 ISI installed. The attached plot compares DARM before and after the vent and the CHARD P contribution to DARM before and after the vent.
Turns out the change in CHARD noise may have actually directly reduced some noise in DARM. The DARM/CHARD coupling function remained the same before and after the vent, so the improvement is directly due to the reduction of noise in CHARD.
We were running HAM1 feedforward to the pitch ASC before the install, but it varied in performance. My plot in the linked alog shows the best performance achieved, but looking at the data closer to the vent, the noise in CHARD P may have been higher than the best performance I show in the linked alog above.
The low frequency noise in DARM has also changed for other reasons:
- DHARD is now on two sensors, reducing the DHARD noise by rt2 (85774)
- MICH ASC has better low pass filters engaged (85893)
- CSOFT P has better low pass filters engaged (85823)
- Improved LSC feedforward (86481, 86370, 86423)
- PEM team sourced and reduced some large peaks (86257)
