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Entry  Sun Apr 29 22:53:06 2018, gautam, Update, General, DARM actuation estimate darmEst.pdf
    Reply  Tue May 1 19:37:50 2018, gautam, Update, General, DARM actuation estimate darmEst.pdfdarmEst_time.pdf
       Reply  Mon May 7 16:23:06 2018, gautam, Update, General, DARM actuation estimate darmProj.pdf37.pngMCalign_20180507.png
          Reply  Mon May 7 20:01:14 2018, Rorpheus, Update, General, Use anti-dewhitening + show CARMA/DARMA 
             Reply  Thu May 10 14:13:22 2018, gautam, Update, General, More refinement of DARM control signal projection darmProj.pdfdarmOLTF.pdfDWcomparison.pdf
                Reply  Fri May 11 13:58:42 2018, rana, Update, General, More refinement of DARM control signal projection 
                   Reply  Fri May 11 19:02:52 2018, gautam, Update, General, More refinement of DARM control signal projection darmProj.pdfdarmOLTF.pdfDWcomparison.pdfDARMsuppression.pdfControlLoop.pdf
                      Reply  Sat May 12 10:02:03 2018, rana, Update, General, More refinement of DARM control signal projection 
                         Reply  Sun May 20 17:43:01 2018, rana, Update, Electronics, How to choose resistors 
                      Reply  Mon May 14 18:58:32 2018, Kevin, Update, PonderSqueeze, Squeezing with no SRM homodyne_heatmap.pdfdisplacement_noise.pdfnoise_budget.pdf
                         Reply  Tue Oct 2 23:57:16 2018, gautam, Update, PonderSqueeze, Squeezing scenarios PonderSqueeze_NB_LORIN.pdf
                   Reply  Tue May 15 21:56:57 2018, gautam, Update, General, Stack measurement setup decommissioned 
                      Reply  Thu May 17 09:14:38 2018, Steve, Update, General, Stack measurement setup decommissioned Load_Cell_Measurement_Set_Up.jpgETMX_stack_up_down.png
Message ID: 13831     Entry time: Thu May 10 14:13:22 2018     In reply to: 13823     Reply to this: 13833
Author: gautam 
Type: Update 
Category: General 
Subject: More refinement of DARM control signal projection 

Summary:

  1. It seems that after a x10 increase in the coil driver resistance, we will have enough actuation range to control (anti de-whitened) DARM without saturating the DAC.
  2. The Barry puck doesn't seem to help us much in reducing the required RMS for DARM control. If this calculation is to be believed, it actually makes the RMS actuation a little bit higher.

See Attachment #1 for the projected control signal ASDs. The main assumption in the above is that all other control loops can be low-passed sufficiently such that even with anti-dewhitening, we won't run into saturation issues.

DARM control loop:

  • I'm now calculating the DARM control signal in counts after factoring into account a digital DARM control loop.
  • The loop shape is what we used when the DRFPMI was locked in Oct 2015.
  • I scaled the overall OLTF gain to have a UGF around 200Hz.
  • The breakdown of how the DARM loop is constructed is shown in Attachment #2.

De-whitening and Anti-De-whitening:

  • The existing DW shape in the ITM and ETM signal chains has ~80dB attenuation around 100 Hz.
  • Assuming ~5uV/rtHz noise from the DAC, 60dB of low-passing gets us to 5nV/rtHz. With 4.3kohm series resistance, this amounts to ~1pA/rtHz current noise (compared to ~3pA/rtHz from the Johnson noise of the series resistance). Actually, I measured the DAC noise to be more like ~700nV/rtHz at 100 Hz, so the current noise contribution is only 0.16pA/rtHz.
  • This amounts to getting rid of the passive filter at the end of the chain in the de-whitening board.
  • Attachment #3 shows the existing and proposed filter shapes.

It remains to add the control signals for Oplev, local damping, and ASC to make sure we have sufficient headroom, but given that current projections are predicting using up only ~1000cts of the ~23000cts (RMS) available from the DAC, I think it is likely we won't run into saturations. Need to also figure out what the implication of the reduced actuation range will be on handling the locking transient.

Attachment 1: darmProj.pdf  208 kB  Uploaded Thu May 10 15:24:43 2018  | Hide | Hide all
darmProj.pdf
Attachment 2: darmOLTF.pdf  28 kB  Uploaded Thu May 10 15:24:58 2018  | Hide | Hide all
darmOLTF.pdf
Attachment 3: DWcomparison.pdf  125 kB  Uploaded Thu May 10 19:23:10 2018  | Hide | Hide all
DWcomparison.pdf
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