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Message ID: 409     Entry time: Wed Nov 24 01:53:10 2010
Author: tara 
Type: DailyProgress 
Category: NoiseBudget 
Subject: Intensity Servo 

I modified Dmass' intensity servo, but the servo is not working yet.


We want an intensity stabilizing servo, such that the UGF of the whole OLG TF is ~ 30kHz. So I need to build a servo to meet this requirement.

The OLG  TF of the current actuator to PMC trans PD was plotted in the previous entry. The slope around 30kHz goes like 1/f^3

so I need a servo with a slope of f^2 around 30 kHz to compensate, and get the total slope of 1/f for stability.


The designed servo consists of double stages of simple one zero- one pole TFs, where the corners frequency are 20 kHz (zero) and 70 kHz (pole) for both stages. 

See fig 1 for (a) simulated TF of the designed ISS servo, (b)TF from current actuator and the servo, and (c) sum of (a) and (b).

If we increase the gain so that the UGF is 25 kHz, PM is 40 degree. and if UGF is 30 kHz, PM is 27 degree.

PM is too small. I might need to modify it later.

The ISS filter I need is fairly simple, see fig 2.

The schematic for the ISS I got from Dmass is here. I modified the top part of the schematic for my use.

After the modification, I measrued the TF of the intensity servo part. The TF looks nonsense. I have to check what did I do wrong.





Attachment 1: Tot_TF.png  14 kB  Uploaded Wed Nov 24 03:10:22 2010  | Hide | Hide all
Attachment 2: servo.png  14 kB  Uploaded Wed Nov 24 03:33:19 2010  | Hide | Hide all
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