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MIF (Noise Budget)

satoshi.tanioka - 13:38 Monday 30 April 2018 (4905)

PR2 optical lever control loops

Izumi-san, Enomoto-san and Tanioka

As Izumi-san reported yesterday, the PR2 control loops show high coherence with the interferometer readout in the frequency band from 10 Hz to about 30 Hz(4895). So we tried to reduce these noise by changing the filters. Adjusting the gain and low pass filter, we tuned the UGF around 3 Hz both PITCH and YAW. Attached figure shows the before and after of TFs.

After that, the sensitivity around 20 Hz is improved as shown in attached graph. However, as the DC gain became smaller, RMS of TM got worse and the sensitivity also got worse at some frequwncy range. We have to improve the filters.

Also, we noticed that Periodic noise at 44 Hz (4891) disappeared after changing the filter. This noise can couple through PR2 optical lever control loops.

Images attached to this report

Comments to this report:

kiwamu.izumi - 9:36 Tuesday 01 May 2018 (4916)

Earlier in this morning, we had another look at the new optical lever control filters that Tanioka-kun implemented yesterday.

The first attachment (shown below) shows a comparison of the MICH spectrum either with the old control filter or the new filter.

While noise between 10 and 30 Hz clearly reduced with the new control filter, the bump at around 100 Hz remained the same. This indicates that the dominant noise at around 100 Hz is not from the PR2 optical lever.

The second attachment shows the optical lever readout either with the new or the old filter. As reported by Tanioka-kun (4905), the rms increased for both pitch and yaw by a factor of few.

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