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Entry  Mon Jul 19 14:14:03 2010, nancy, koji, Update, IOO, QPD Response Transfer Function 
    Reply  Mon Jul 19 14:16:01 2010, nancy, koji, Update, IOO, QPD Response Transfer Function QPDTF2.png
Message ID: 3244     Entry time: Mon Jul 19 14:14:03 2010     Reply to this: 3245
Author: nancy, koji 
Type: Update 
Category: IOO 
Subject: QPD Response Transfer Function 

Friday night myself and Koji measured the Transfer function of the QPD circuit at MC2 side using a chopper . Following was our procedure :

 

We connected some wires at the input and output of the filter circuit to one of the segment of teh QPD. - seg 1.

A laser light was shined on to the QPD, it was pulsed using a chopper. The frequency of rotation of the chopper was varied.

These wires were then fed to the spectum analyser , and a transfer funstion was observed, It was nearly a low pass filter

The chopper frequency was then made variable by giving the chopper a signal from the spectrum analyser. This signal just swiped a large range of the rpm of the chopper.

Now the input signal looked like a sine wave of varying frequency. the transfer function looked like a perfect LPF, with a small SNR.

Attaching the plot of the TF in the next e-log (this one is on windows and can't access /cvs/cds)

 

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