Reports until 15:58, Tuesday 24 January 2023
H1 ISC (CDS)
jeffrey.kissel@LIGO.ORG - posted 15:58, Tuesday 24 January 2023 - last comment - 12:20, Wednesday 01 February 2023(66980)
H1 OMC DCPD Analog Whitening Chassis Changed from D2100630 Assembly to D2200215 Assembly
L. Dartez, J. Kissel, F. Mera, M. Pirello, D. Schaetzl, D. Sigg
IIET Ticket 24198
WP 10933

In order to take advantage of the new low-noise, fast, 18-bit ADC (that we also switched over to today; LHO:66974), and improve the headroom for violin modes (among several other excellent new user-interface and noise advantages), we've swapped the out the first attempt at the A+ era whitening chassis (D2100630-v3) for the newly arrived second attempt at the A+ era whitening chassis (D2200215) for the primary, OMC DCPD signals coming out of the vacuum system.

We've installed the new chassis -- serial number S2300002 -- under the previous version in ISC-R5 U-height U24. Once installed, we moved all of the relevant cable connections from the previous chassis (S2101608) and plugged them into the front and back of new chassis.

There were some hiccups after connecting the DCPDs to front-end of the whitening chassis -- namely the current limiting resistor in the power regulator circuit (that which reduces the chassis input +18V to the +15V that the preamp) became current limited, and was dragging down the voltage supplied to the DCPDs to a measly 2V. Dean first ID's the problem because the status LED on the front panel became "barely lit" after the chassis was powered on *with* the DCPDs connected. We then spent a bit of time understand what was happening, including measuring the current draw of the DCPDs (using the old chassis, in-situ, chassis power and DCPD power on, measuring the current draw at the output of the regulator by measuring voltage across the 10 mOhm resistors R55 R68 R81, using the available surrounding test points).

   Supply          Current draw
  Regulator          at Output
    +18 to +15V:      120 mA
    -18 to -15V:       80 mA
    +18 tp  +5V:       50 mA

Finding this, and seeing with our own eyes (after pulling S2101608 from the rack and popping the lid) that our S2101608 instantiation of D2100630 chassis had an undocumented (no e-traveler update, no drawing update, no aLOG) change of the current limiting resistor on the +15 V regulator (R61 on page 7 of D2100630-v3) from 1.5 kOhm down to 499 Ohm, increasing the current limit from 100 mA to 250 mA, we made an on-the-fly design change/choice to replace the equivalent resistor in the new chassis assembly -- R8 in D2200045 -- with 750 Ohm, and thus we now have a current limit of 200 mA on this +15V supply leg. Dean has already graciously already updated D2200045 to -v2 with this change.

To be covered in separate aLOGs / Comments:
    - Pictures of the chassis installed in the rack
    - Measurements of the frequency response in calibration-group level detail
    - Fits and subsequent compensation of that response
    - Comments about the output voltage noise
    - Comments about a new output voltage offset
    - Comments about the full chain's OMC DCPD dark noise w.r.t. the new ADC noise
    - Comments about using the remote full-chain driven excitation test system to confirm that the compensation is still relatively flat
    - Comments about changes needed to be done to the Beckhoff system to regain remote control of the chassis
 
Comments related to this report
jeffrey.kissel@LIGO.ORG - 16:06, Tuesday 24 January 2023 (66986)
Here're a few photos showing the position of the new whitening chassis in the ISC-R5 rack, among the cluster of racks that are a bit +X/-Y of HAM6.
Images attached to this comment
daniel.sigg@LIGO.ORG - 16:18, Tuesday 24 January 2023 (66989)

The compensated transfer functions of both DCPD_A and DCPD_B using the test inputs look pretty flat. 

This compares to the past measurement in alog 62250.

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jeffrey.kissel@LIGO.ORG - 12:20, Wednesday 01 February 2023 (67154)CAL, CDS, ISC
J. Kissel

I've copied over Daniel's measurement template/results from LHO:66989 above, which he had saved to
    /ligo/home/daniel.sigg/Desktop/DCPD/
        DCPD_230124_C.xml
to the location I've been storing these results in the calibration group's svn, under
    /ligo/svncommon/CalSVN/aligocalibration/trunk/Common/Electronics/H1/SensingFunction/OMCA/Data/
        20230124_H1_TIAxWC_OMCA_S2100832_S2300002_DCPDAandB_RemoteTestChainEXC_tf.txt
        20230124_H1_TIAxWC_OMCA_S2100832_S2300002_DCPDAandB_RemoteTestChainEXC.xml
    
the text file is a 5-column file, whose columns are [Freq Re(DCPD A) Im(DCPD A) Re(DCPD B) Re(DCPD B)].

Here, I also post the results in non-dB units so you can directly read off the percentage of flatness.

Note -- this measurement is already out-of-date. This data was taken with the same in-vac transimpedance amplifier as we've had since Feb 2022, S2100832. However, the data was taken with the higher-noise components of the  whitening chassis, S2300002, which we replaced for a lower noise version, S2300003 yesterday, 2023-01-31 (see 67110 and LHO:67119). I'm also unsure of how long the whitening chassis / transimpedance amplifier had been powered on when Daniel took this measurement -- and we know that the transimpedance amplifier's response changes while it's large inductors thermalize.

So -- we should take this measurement again (and record the state of the electronics a little more carefully).
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