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Entry  Wed Dec 23 16:34:25 2009, Koji, Update, IOO, MCT QPD/MC REFL QPD disabled 
    Reply  Thu Dec 24 19:13:29 2009, Koji, Update, IOO, MCT QPD investigation D990692.png
       Reply  Sun Dec 27 23:44:59 2009, rana, Update, Electronics, MCT QPD investigation 
          Reply  Mon Dec 28 01:17:01 2009, Koji, Update, Electronics, MCT QPD investigation 
Message ID: 2454     Entry time: Sun Dec 27 23:44:59 2009     In reply to: 2451     Reply to this: 2455
Author: rana 
Type: Update 
Category: Electronics 
Subject: MCT QPD investigation 


I found that MCT QPD has dependence of the total output on the position of the spot. Since the QPD needs the supply and bias voltages from the sum/diff amp, I could not separate the problems of the QPD iteself and the sum/diff amplifier by the investigation on Tuesday. On Wednesday, I investigated a generic quad photodiode interface module D990692.

 This is indeed sad. But, we can perhaps bypass all of this by just using the individual segment outputs. According to the circuit diagram and the c1iool0 .db file, we should be able to just do the math on the segments and ignore the VERT/HOR/SUM signals completely. In that case, we can just use high impedance for the sum/diff buffers as Koji says and not suffer from the calibration errors at all I think.

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