Aidan. Nutsinee

Summary:

The CO2 ITMX ISS AC anti-whitening filters where previously (naively) set up with the complete inverse of the ISS whitening filters in the electronics. This included a pole at zero, or an integrator. This caused problems at LLO when turned on as residual DC in the input to that channel was steadily integrated over time. We fixed this problem at LLO by moving the pole from 0 Hz to 1 Hz. I added the same fix here. Also, these filters were missing from the ITMY channels, so I added them at LHO as well.

Details:

In Foton, I loaded H1TCSCS.TXT and, in the following four channels,

• ITMX_CO2_ISS_IN_AC
• ITMX_CO2_ISS_OUT_AC
• ITMY_CO2_ISS_IN_AC
• ITMY_CO2_ISS_OUT_AC

I set the first three filter modules to:

• gain255 = gain(0.0039)
• HF78344 = zpk([200],[1],0.000013,"n")
• HF152 = zpk([200],[1],0.0066,"n")

The key change being the removal of a pole at zero and the addition of a pole at 1Hz.

After saving the file, I hit "Clear History" and "Load Coefficients" on all four channels.

Additional information:

The ISS AC channels tell us the intensity noise on the CO2 lasers. We're particularly interested in the region 10-200 Hz where we may couple noise into DARM.