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40m Log |
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Wed Apr 26 01:00:23 2017, gautam, Update, General, DRMI locking  
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Fri Apr 28 02:04:36 2017, gautam, Update, General, DRMI locking
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Fri Apr 28 13:56:26 2017, rana, Update, General, DRMI locking
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Mon May 1 16:29:51 2017, gautam, Update, General, DRMI locking 
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Mon May 1 21:45:54 2017, ericq, Update, General, DRMI locking
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Wed May 3 18:45:45 2017, rana, Update, General, DRMI locking
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Thu May 4 19:03:15 2017, gautam, Update, General, DRMI locking - preliminary MICH NB   
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Fri May 5 10:13:02 2017, ericq, Update, General, MICH NB questions
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Fri May 5 12:10:53 2017, gautam, Update, General, MICH NB questions
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Sat May 6 21:52:11 2017, rana, Update, General, MICH NB questions
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Wed May 10 01:56:06 2017, gautam, Update, General, MICH NB - OL coupling  
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Wed May 10 16:53:38 2017, rana, Update, General, MICH NB - OL coupling
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Wed May 10 17:17:05 2017, gautam, Update, General, DAC / Coil Driver noise
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Wed May 10 17:46:44 2017, gautam, Update, General, DAC / Coil Driver noise - SRM coil driver + dewhite board removed
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Thu May 11 09:45:46 2017, rana, Update, General, DAC / Coil Driver noise - SRM coil driver + dewhite board removed
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Thu May 11 18:59:22 2017, gautam, Update, General, SRM coil driver + dewhite board initial survey 
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Fri May 12 01:36:04 2017, gautam, Update, General, SRM coil driver + dewhite board LISO modeling 
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Fri May 12 12:34:55 2017, gautam, Update, General, ITM and BS coil driver + dewhite board pulled out
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Fri May 12 18:50:08 2017, gautam, Update, General, ITM and BS coil driver + dewhite board pulled out
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Mon May 22 13:37:01 2017, gautam, Update, General, DAC noise estimate 
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Tue May 23 22:58:23 2017, gautam, Update, General, De-Whitening board noises
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Thu May 25 19:27:29 2017, gautam, Update, General, Coil driver board noises
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Mon May 29 16:47:38 2017, gautam, Update, General, Coil driver boards reinstalled  
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Tue May 30 16:02:59 2017, gautam, Update, General, Coil driver boards reinstalled
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Thu Jun 1 00:10:15 2017, gautam, Update, General, Coil driver boards reinstalled
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Fri Apr 28 19:32:06 2017, gautam, Update, General, DRMI locking - PRCL angular FF 
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Message ID: 12987
Entry time: Fri May 12 01:36:04 2017
In reply to: 12986
Reply to this: 12988
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Author: |
gautam |
Type: |
Update |
Category: |
General |
Subject: |
SRM coil driver + dewhite board LISO modeling |
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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).
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Attachment 2: |
liso.zip
314 kB
Uploaded Fri May 12 02:36:36 2017
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