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Message ID: 60     Entry time: Sun Nov 4 23:22:50 2007
Author: waldman 
Type: Update 
Category: OMC 
Subject: OMC PZT and driver response functions 
I wrote a big long elog and then my browser hung up, so you get a less detailed entry. I used Pinkesh's calibration of the PZT (0.9 V/nm) to calibrate the PDH error signal, then took the following data on the PZT and PZT driver response functions.:

  • FIgure 1: PZT dither path. Most of the features in this plot are understood: There is a 2kHz high pass filter in the PZT drive which is otherwise flat. The resonance features above 5 kHz are believed to be the tombstones. I don't understand the extra motion from 1-2 kHz.
  • Figure 2: PZT dither path zoom in. Since I want to dither the PZT to get an error signal, it helps to know where to dither. The ADC Anti-aliasing filter is a 3rd order butterworth at 10 kHz, so I looked for nice flat places below 10 KHz and settled on 8 kHz as relatively harmless.
  • Figure 3: PZT LSC path. This path has got a 1^2:10^2 de-whitening stage in the hardware which hasn't been digitally compensated for. You can see its effect between 10 and 40 Hz. The LSC path also has a 160 Hz low path which is visible causing a 1/f between 200 and 500 Hz. I have no idea what the 1 kHz resonant feature is, though I am inclined to point to the PDH loop since that is pretty close to the UGF and there is much gain peaking at that frequency.
Attachment 1: 071103DitherShape.png  40 kB  | Hide | Hide all
Attachment 2: 071103DitherZoom.png  44 kB  | Hide | Hide all
Attachment 3: 071103LSCShape.png  32 kB  | Hide | Hide all
Attachment 4: 071103DitherShape.pdf  180 kB  | Hide | Hide all
Attachment 5: 071103DitherZoom.pdf  108 kB  | Hide | Hide all
Attachment 6: 071103LSCShape.pdf  34 kB  | Hide | Hide all
Attachment 7: 071103LoopShape.pdf  37 kB  | Hide | Hide all
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