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Entry  Tue Jun 29 23:56:38 2010, tarac, Notes, PMC, PMC servo debugging 
    Reply  Wed Jun 30 00:37:49 2010, rana, HowTo, Computers, PMC servo debugging 
       Reply  Wed Jun 30 00:59:13 2010, Frank, HowTo, Computers, PMC servo debugging 
Message ID: 187     Entry time: Tue Jun 29 23:56:38 2010     Reply to this: 188
Author: tarac 
Type: Notes 
Category: PMC 
Subject: PMC servo debugging 

 I was going to check the TF on each stage of PMC's servo.

Unfortunately, I couldn't find the floppy disc drive, so I slide the sliders (gain, RF power) around. When I add more RF power (from 1V to 7V) to 21.5 MHz EOM, the oscilaltion subsides*.

(*5 mins later I came back to turn down the RF power to 1 V again, and the beam was perfectly locked for a few minutes before fluctuated again)

It's not a long term solution, but I note this for further debugging.

One thing about the gain, I see the TF of the whole PMC servo, when I increase the common gain from 0 to ~8 dB, the magnitude of the TF gets higher. If I increase more gain to ~ 10dB or something, the magnitude goes down . So there might be sth wrong about the opamp that controls the gain.

 

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