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Message ID: 1080     Entry time: Thu Sep 23 17:45:56 2010
Author: Alastair & Zach 
Type: Electronics 
Category: GYRO 
Subject: pdh box 1 mods 

 We changed feedback resistor R24 back to 1k.  The high frequency weirdness went away.

Next we changed the capacitor C6 to 1.5nF in order to move the pole frequency back up to around 98MHz.  I just bodged in a thin film capacitor for now and we'll replace this with a plastic one.  We then changed R16 to 750k to move the low pole back down in frequency (note - this doesn't quite move it back to where it was before but since this resistor gets switched out by the boost stage it shouldn't be critical).  The box is back in the system and the locking on the CCW loop is clearly better.  Next we'll take a TF of the closed loop gain.

Here is the transfer function for the box as it is now.  We couldn't go down to 10Hz because the box saturates.

Attachment 1: pdh1ampl.png  6 kB  | Hide | Hide all
Attachment 2: pdh1phase.png  6 kB  | Hide | Hide all
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