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Entry  Thu Aug 20 00:21:51 2020, gautam, Update, Electronics, First look at HV coil driver IMG_8724.JPGtimeDomain.pdfHVampNoise.pdf
    Reply  Sun Aug 23 23:36:58 2020, gautam, Update, Electronics, First look at HV coil driver IMG_5379.JPGstabilityCriterion.pdf
       Reply  Wed Aug 26 16:12:25 2020, gautam, Update, Electronics, Test mass coil current requirements coilCurrents.png
       Reply  Tue Sep 1 15:39:04 2020, gautam, Update, Electronics, HV coil driver oscillations fixed testSetup.pdfHVampNoise_driven.pdf
          Reply  Thu Oct 22 11:14:47 2020, gautam, Update, Electronics, HV coil driver packaged into 2U chassis HVampNoise_driven_chassis.pdfHVampNoise_dispUnits.pdfD1900163_measurementSetup.zip
             Reply  Thu Oct 22 13:04:42 2020, rana, Update, Electronics, HV coil driver packaged into 2U chassis 
                Reply  Thu Oct 22 22:01:53 2020, gautam, Update, Electronics, HV coil driver packaged into 2U chassis DACnoiseFilterGain.pdfDACnoiseFilterNoises.pdf
                   Reply  Fri Oct 23 09:03:43 2020, anchal, Update, Electronics, HV coil driver packaged into 2U chassis 
             Reply  Thu Nov 12 14:55:35 2020, gautam, Update, Electronics, More systematic noise characterization powerSupplyNoise.pdfcoherence.pdf
                Reply  Thu Nov 12 15:40:42 2020, Koji, Update, Electronics, More systematic noise characterization 
                   Reply  Mon Nov 16 00:02:34 2020, rana, Update, Electronics, More systematic noise characterization 
                      Reply  Wed Jan 20 10:13:06 2021, gautam, Update, Electronics, HV Power supply bypassing bypassCaps.pdfIMG_9079.jpgIMG_9078.jpgHVampNoise_driven_chassis.pdfprintCoilCurrents.pdf
                         Reply  Mon Feb 1 12:30:21 2021, gautam, Update, Electronics, More careful characterization HVPS.pdfHV_testckt.pdftotalNoise.pdf
                         Reply  Wed Feb 10 21:14:03 2021, gautam, Update, Electronics, Production version of the HV coil driver tested inputDiffRecTF.pdfLVnoises.pdftotalNoise.pdftimeDomainTests.pdf
                            Reply  Fri Feb 26 16:31:02 2021, gautam, Update, Electronics, Production version of the HV coil driver tested with KEPCO HV supplies totalNoise_KEPCO.pdf
                               Reply  Fri Feb 26 20:20:43 2021, Koji, Update, Electronics, Production version of the HV coil driver tested with KEPCO HV supplies 
                                  Reply  Sat Feb 27 17:25:42 2021, gautam, Update, Electronics, Production version of the HV coil driver tested with KEPCO HV supplies 
                                     Reply  Thu May 20 16:56:21 2021, Koji, Update, Electronics, Production version of the HV coil driver tested with KEPCO HV supplies P_20210520_154523_copy.jpg
Message ID: 15542     Entry time: Wed Aug 26 16:12:25 2020     In reply to: 15536
Author: gautam 
Type: Update 
Category: Electronics 
Subject: Test mass coil current requirements 

Attachment #1 is a summary of the current to each coil on the suspensions. The situation is actually a little worse than I remembered - several coils are currently drawing in excess of 10mA. However, most of this is due to a YAW correction, which can be fixed somewhat more easily than a PIT correction. So I think the circuit with a gain of 31 for an input range of +/-10 V, which gives us the ability to drive ~12mA per coil through a 25kohm series resistor, will still provide sufficient actuation range. As far as the HV supplies go, we will want something that can do +/- 350 V. Then the current to the coils will at most be ~50 mA per optic. The feedback path will require roughly the same current. The quiescent draw of each PA95 is ~10mA. So per SOS suspension, we will need ~150mA.

If it turns out that we need to get more current through the 25kohm series resistance, we may have to raise the voltage gain of the circuit. Reducing the series resistance isn't a good option as the whole point of the circuit is to be limited by the Johnson noise of the series resistance. Looking at these numbers, the only suspension on which we would be able to plug in a HV coil driver as is (without a vent to correct for YAW misalignment) is ITMY.


Update 2 Sep 2020 2100: I confirmed today that the number reported in the EPICS channel, and the voltage across the series resistor, do indeed match up. The test was done on the MC3 coil driver as it was exposed and I didn't need to disable any suspensions. I used a Fluke DMM to measure the voltage across the resistor. So there is no sneaky factor of 2 as far as the Acromag DACs are concerned (unlike the General Standards DAC).

Attachment 1: coilCurrents.png  158 kB  Uploaded Wed Aug 26 17:52:57 2020  | Hide | Hide all
coilCurrents.png
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