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Message ID: 16275     Entry time: Wed Aug 11 11:35:36 2021
Author: Paco 
Type: Update 
Category: LSC 
Subject: PRMI MICH orthogonality plan 

[yehonathan, paco]

Yesterday we discussed a bit about working on the PRMI sensing matrix.

In particular we will start with the "issue" of non-orthogonality in the MICH actuated by BS + PRM. Yesterday afternoon we played a little with the oscillators and ran sensing lines in MICH and PRCL (gains of 50 and 5 respectively) in the times spanning [1312671582 -> 1312672300], [1312673242 -> 1312677350] for PRMI carrier and [1312673832 -> 1312674104] for PRMI sideband. Today we realize that we could have enabled the notchSensMat filter, which is a notch filter exactly at the oscillator's frequency, in FM10 and run a lower gain to get a similar SNR. We anyways want to investigate this in more depth, so here is our tentative plan of action which implies redoing these measurements:

Task: investigate orthogonality (or lack thereof) in the MICH when actuated by BS & PRM
    1) Run sensing MICH and PRCL oscillators with PRMI Carrier locked (remember to turn NotchSensMat filter on).
    2) Analyze data and establish the reference sensing matrix.
    3) Write a script that performs steps 2 and 3 in a robust and safe way.
    4) Scan the C1:LSC-LOCKIN_OUTMTRX, MICH to BS and PRM elements around their nominal values.
    5) Scan the MICH and PRCL RFPD rotation angles around their nominal values.

We also talked about the possibility that the sensing matrix is strongly frequnecy dependant such that measuring it at 311Hz doesn't give us accurate estimation of it. Is it worthwhile to try and measure it at lower frequencies using an appropriate notch filter?

Wed Aug 11 15:28:32 2021 Updated plan after group meeting

- The problem may be in the actuators since the orthogonality seems fine when actuating on the ITMX/ITMY, so we should instead focus on measuring the actuator transfer functions using OpLevs for example (same high freq. excitation so no OSEM will work > 10 Hz).

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