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Entry  Wed Apr 26 01:00:23 2017, gautam, Update, General, DRMI locking  DRMI_1f_26April2017.pngIMG_7373.JPGIMG_7372.JPG
    Reply  Fri Apr 28 02:04:36 2017, gautam, Update, General, DRMI locking  20170428_DRMI.pdf
       Reply  Fri Apr 28 13:56:26 2017, rana, Update, General, DRMI locking  
          Reply  Mon May 1 16:29:51 2017, gautam, Update, General, DRMI locking  LSC_sensingNoise.pdfIMG_7378.JPG
             Reply  Mon May 1 21:45:54 2017, ericq, Update, General, DRMI locking  
                Reply  Wed May 3 18:45:45 2017, rana, Update, General, DRMI locking  
                   Reply  Thu May 4 19:03:15 2017, gautam, Update, General, DRMI locking - preliminary MICH NB DRMI_noArms_April30.pdfMICH_OLTF.pdfC1NB_disp_40m_MICH_NB_30_April_2017.pdf40m_REFL_RFPDs_efficiency.pdf
                      Reply  Fri May 5 10:13:02 2017, ericq, Update, General, MICH NB questions 
                         Reply  Fri May 5 12:10:53 2017, gautam, Update, General, MICH NB questions C1NB_disp_40m_MICH_NB_30_April_2017.pdf
                            Reply  Sat May 6 21:52:11 2017, rana, Update, General, MICH NB questions 
                               Reply  Wed May 10 01:56:06 2017, gautam, Update, General, MICH NB - OL coupling OL_BS_ITM_comp.pdfC1NB_disp_40m_MICH_NB_8_May_2017.pdfC1NB_disp_40m_MICH_NB_10_May_2017.pdf
                                  Reply  Wed May 10 16:53:38 2017, rana, Update, General, MICH NB - OL coupling 
                                  Reply  Wed May 10 17:17:05 2017, gautam, Update, General, DAC / Coil Driver noise actuation.jpg
                                     Reply  Wed May 10 17:46:44 2017, gautam, Update, General, DAC / Coil Driver noise - SRM coil driver + dewhite board removed 
                                        Reply  Thu May 11 09:45:46 2017, rana, Update, General, DAC / Coil Driver noise - SRM coil driver + dewhite board removed 
                                           Reply  Thu May 11 18:59:22 2017, gautam, Update, General, SRM coil driver + dewhite board initial survey D010001-B_40m.pdfD000183-C8_40m.pdf
                                              Reply  Fri May 12 01:36:04 2017, gautam, Update, General, SRM coil driver + dewhite board LISO modeling SRM_bypass_plus_CoilDriver.pdfliso.zip
                                                 Reply  Fri May 12 12:34:55 2017, gautam, Update, General, ITM and BS coil driver + dewhite board pulled out 
                                                    Reply  Fri May 12 18:50:08 2017, gautam, Update, General, ITM and BS coil driver + dewhite board pulled out 
                                                       Reply  Mon May 22 13:37:01 2017, gautam, Update, General, DAC noise estimate DAC_noise_model.pdfC1NB_disp_40m_MICH_NB_22_May_2017.pdf
                                                          Reply  Tue May 23 22:58:23 2017, gautam, Update, General, De-Whitening board noises ITMX_deWhite_ch1_noise.pdf
                                                             Reply  Thu May 25 19:27:29 2017, gautam, Update, General, Coil driver board noises  coilDriverNoises.pdf
                                                                Reply  Mon May 29 16:47:38 2017, gautam, Update, General, Coil driver boards reinstalled deWhitening_consolidated.pdfdeWhitening_measurements.zipETMY_OL.png
                                                                   Reply  Tue May 30 16:02:59 2017, gautam, Update, General, Coil driver boards reinstalled OL_noiseInjection.pdf
                                                                      Reply  Thu Jun 1 00:10:15 2017, gautam, Update, General, Coil driver boards reinstalled 
       Reply  Fri Apr 28 19:32:06 2017, gautam, Update, General, DRMI locking - PRCL angular FF PRC_angularFF.pdfPRC_TFs.pdf
Message ID: 12987     Entry time: Fri May 12 01:36:04 2017     In reply to: 12986     Reply to this: 12988
Author: gautam 
Type: Update 
Category: General 
Subject: SRM coil driver + dewhite board LISO modeling 

I've made the LISO models for the dewhitening board and coil driver boards I pulled out.

Attached is a plot of the current noise in the current configuration (i.e. dewhitening board just has a gain x3 stage, and then propagated through the coil driver path), with the top 3 noise contributions: The op-amps (op3 and op5) are the LT1125s on the coil driver board in the bias path, while "R12" is the Johnson noise from the 1k input resistace to the OP27 in the signal path.

Assuming the OSEMs have an actuation gain of 0.016 N/A (so 0.064 N/A for 4 OSEMs), the current noise of ~1e-10 A/rtHz translates to a displacement noise of ~3e-15m/rtHz at ~100Hz (assuming a mirror mass of 0.25kg). 

I have NOT included the noise from the LM6321 current buffers as I couldn't find anything about their noise characteristics in the datasheet. LISO files used to generate this plot are attached.

Quote:

I've added marked-up schematics + high-res photographs of the SRM coil driver board and dewhitening board to the 40m DCC Document tree (D1700217 and D1700218). 

In the attached marked-up schematics, I've also added the proposed changes which Rana and I discussed earlier today. For the thick-film -> thin-film resistor switching, I will try and make a quick LISO model to see if we can get away with replacing just a few rather than re-stuff the whole board.

Since I have the board out, should I implement some of these changes (like AD797 removal) before sticking it back in and pulling out one of the ITM boards? I need to look at the locking transients and current digital limit-values for the various DoFs before deciding on what is an appropriate value for the output resistance in series with the coil.

Another change I think should be made, but I forgot to include on the markups: On the dewhitening board, we should probably replace the decoupling capacitors C41 and C52 with equivalent value electrolytic caps (they are currently tantalum caps which I think are susceptible to fail by shorting input to output).

 

Attachment 1: SRM_bypass_plus_CoilDriver.pdf  78 kB  | Hide | Hide all
SRM_bypass_plus_CoilDriver.pdf
Attachment 2: liso.zip  314 kB  Uploaded Fri May 12 02:36:36 2017
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