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Entry  Sat Nov 12 03:46:55 2011, Suresh, Update, IOO, MC WFS Servo: Open loop gain  WFS1_PIT_servo_filtershape_20111111_1.pngWFS1_PIT_servo_OLG_20111111_1.pngError_signal_WFS1_PIT_20111111_1.png
    Reply  Sat Nov 12 08:09:47 2011, rana, Update, IOO, MC WFS Servo: Open loop gain  
       Reply  Tue Nov 15 01:44:36 2011, Suresh, Update, IOO, MC WFS Servo: Open loop gain  WFS1PIT_OL_gain.png
Message ID: 5883     Entry time: Sat Nov 12 03:46:55 2011     Reply to this: 5884
Author: Suresh 
Type: Update 
Category: IOO 
Subject: MC WFS Servo: Open loop gain  

[Mirko, Suresh]

I closed the WFS loops and measured the transfer function from IN2 to IN1 testpoints on the WFS1_PIT filterbank. 

We looked at the filter shape consisting of

1) Integrator: zpk([0.8],[0],0.8,"n")

2) zpk([0.8],[100,100],1,"n")

3) zpk([1:10],[3,30],1,"n")

The combined filter shape (along with an added pendulum filter, zpk([ ],0.8,1,"n")  ) is given below

WFS1_PIT_servo_filtershape_20111111_1.png

 

The OL Transfer function measured for WFS1_PIT loop is

WFS1_PIT_servo_OLG_20111111_1.png

 The blue reference is a measurement  without the third "45 deg" filter in the list above.  Without it the UGF is around 1.5Hz and increasing the gain results in additional noise from the servo bump seen in the earlier elog .  With it the UGF is around 3Hz.

The supression of the error signal is shown here

 Error_signal_WFS1_PIT_20111111_1.png

The other WFS loops are expected to have a similar behaviour with the exception of the MC2 QPD channels.  I will measure their OLTF shortly and then proceed with the inclusion of the QPD sensors into the WFS system.

 

 

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