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Entry  Sat Nov 26 02:15:42 2011, Mirko, Update, SUS, Not adaptive, still cool PendulumQ0.1HzWithElip2comma5HzLpWfsOnCorrectedShape.pdfVirtualPendulumFilterShape.pdfSetupVirtualPendulumV2.png
    Reply  Thu Dec 1 03:27:39 2011, Mirko, Update, SUS, Not adaptive, still cool 
Message ID: 6057     Entry time: Thu Dec 1 03:27:39 2011     In reply to: 6014
Author: Mirko 
Type: Update 
Category: SUS 
Subject: Not adaptive, still cool 


[Rana, Mirko]

I tried out the virtual pendulum idea today. The idea is to compensate the physical pendulum via the control system, and then add a virtual pendulum formed in the control system. We know the actuator TF from p. 5900 and apply its inverse to the C1:SUS-MC?_SUSPOS filters. Also we add an pendulum Q=3 with a resonance frequency of 0.1Hz to the POS control loops.

The result is pretty awesome!

1. Black: Standard config. Wfs on. New Cheby filter in place ( p. 6031 )
2. Red: With virtual pendulum. Extra eliptic LP filter @ 2.5Hz


Filter shape:


This is stable for 5-10minutes, at which point it falls out of lock, swinging in yaw.



In the above entry MC_f  signal is improved off of resonance by the implementation of the pendulum compensation. It should be checked if this is actually due to the implementation of the virtual pendulum at 0.1Hz. A way to check that might be to implement a simple double LP at 0.1Hz instead and look at the resulting MC_f signal. A projection of the OSEM FB noises with the compensation active might be interesting.
The physical resonance at 1Hz is clearly not compensated correctly, which is probably the reason for the lock losses after a few minutes. It might be a good start to measure the residual resonance with the compensation in place. The filters in bank 7 of C1:SUS-MC?_SUSPOS have both the compensation of the 1Hz resonance( really the inverse actuator TF ) and the virtual pendulum in them. The ‘pure’ compensation can be found in the InvTF module in the C1:OAF-ADAPT_MCL_CORR filter.
The fact that the beam swings in yaw at lock loss indicates that the separation of the DOFs might not be perfect. One should have a look into the yaw and pitch DOFs with the compensation active.

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