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15802   Wed Feb 10 21:14:03 2021 gautamUpdateElectronicsProduction version of the HV coil driver tested

Summary:

I did what I consider to be a comprehensive set of tests on the production version of the high voltage coil driver circuit. I think the performance is now satisfactory and the circuit is ready for the production build. Barring objections from anyone, I will ask Chub to place an order for components to stuff the 4 necessary units + 1 spare on Friday, 12 Feb (so that people have a full day to comment). A big thanks to Chub and the folks at JLCPCB for dealing with my incessant order requests and patiently supporting this build and letting me turn this around in 10 days - hopefully this is the end of this particular saga.

Schematic is here. All references to component designations are for v4 of the schematic.

Important design changes:

1. All I/O to this board will be via D9 connectors. This will allow bypassing the high voltage stage in future suspensions while retaining the same cable config in the suspension drive, if that is desired. Some re-arrangement of the grouping of coils was also done for consistency with the planned upgrade.
2. Differential receiving for the input signal from the Acromag. The nominal quad opamp is LT1125 but if we find noise issues (which I didn't), the OP497 has compatible PCB footprint.
3. Added input protection dual diode D6 to protect the PA95 as recommended in the datasheet. This should protect the IC if (for example) the HV line isn't plugged in but the Acromag input is non-zero.
4. Increased the feedback resistance from 30kohms to 12kohms. R16 through R21 are now 20k, while the old design had 5k. The purpose is to reduce the current demand in the feedback path, hopefully this opens up the number of DCPS we can use. To keep the overall gain of 31, the resistor R15 was upped from 1kohms to 4kohms.
5. Feedback capacitance reduced from 15 uF to 3 uF. This was largely for space saving / ease of layout on the PCB. The resulting corner frequency is increased slightly from 0.35 Hz to 0.45 Hz but this doesn't have any imapct on the performance of the circuit at frequencies of interest (1/2/pi/R/C had R=30k, C=15uF, now R=120k, C=3uF).
6. Added an R-C-R network at the output of the PA95, before the fast actuation signal is summed and sent to the OSEM coil.
• This is probably the most important change, noise-performance wise.
• The purpose of the network is to passively filter out the excess noise we saw at ~100 Hz (the corner from the 4kohm resistor + 3uF cap is at ~13 Hz, so factor of 10 filtering at 100 Hz, which was deemed sufficient, see earlier elogs in the thread).
• The Johnson noise contribution of the 20 kohm resistor is slightly higher than the original design which had a 25 kohm series resistor (but no R-C-R passive filter at the output of the PA95). But once again, this was deemed to have negligible effect on the performance at frequencies of interest to us.
• The total current driving capability of the circuit is almost unchanged since the 20kohm + 4kohm nearly equals the old 25kohm resistance.
7. Made the Vmon paths for monitoring the HV output of the PA95 differential sending, seems like a good practise to follow for all new designs.
8. Added on-board bypass capacitors (2 x 10uF WIMA film caps) for cleaning up the HV supply noise.

Tests:

A series of tests were done. Note that only 1 channel was stuffed (I am out of PA95s), and the HP power supplies borrowed from Rich were used for the HV rails. For the +/-18V, a regular bench-top unit was used.

1. Low voltage stage tests
• TF of the differential receiving stage was measured and the overall unity gain and corner at 24kHz were verified, see Attachment #1.
• With the input of the circuit grounded, I measured the noise of the circuit at various points (see legends on Attachment #2). I didn't bother to do a detailed verification against a SPICE model as the levels seemed roughly what is expected.
2. Overall noise performance with HV stage enabled
• For a range of drive currents, generated by applying the appropriate voltage using an Acromag XT1541 DAC module to the J1 connector, I measured the voltage on the circuit side of the 20 kohm resistor (by clipping onto the resistor leg. Note that the path to ground for the current was provided by connecting a 20 ohm resistor between pins 1 and 6 on J3a, and then grounding pin 6.
• Results are shown in Attachment #3
• For the drive currents at the edge of the range of operation, there is a small excess relative to lower drive currents. My best hypothesis for why this is happening is that the HV rail is too close to the requested output voltage (the HP units are rated for 320V, which is borderline if we want 300V at the output of the PA95). In any case, the R-C-R passive filter means that above ~60 Hz, there is excellent agreement between model and measurement.
3. Time domain tests
• Used a function generator. to drive a 50 mHz, 3Vpp sine wave to the "Bias Input" (=J1), and monitored (i) pickoff of drive signal, (ii) High voltage output at the circuit side of the 20kohm resistor, and (iii) the Vmon output (=pins 1/6 on J4), all on a 100 MHz Tektronix scope.
• Results shown in Attachment #4. Once again, I see no red flags.
• While I had the unit hooked up to the scope, I also checked the time domain signal with the scope set to 100 ns/div time base. I saw no evidence of any oscillatory features, either when no input signal was applied, or when a DC signal was provided (in which case the scope was set to AC coupling). 👍
4. Checked that the protection diodes at various locations in the circuit work.
5. Checked the pin-mapping on all 6 D9 connectors is consistent with the top level diagram in the schematic.

PCB remarks:

As I was stuffing the board, I noticed a few improvements that can be made. Just noting these here for documentation purposes - these changes are mostly aesthetic and I personally see no need to order another set of PCBs.

1. In some places, the silkscreen designators don't have the correct "orientation" relative to the component they are designating. I didn't find any serious ambiguity in terms of being misled to stuff the wrong component onto the wrong pads, but in the spirit of doing a professional job...
2. The current limiting resistors on the +/-430V LEDs (R37/R38) have footprints for leaded components rather than SMT (which is what the +/-15V LEDs have).
3. R45 and R46, the current limiting resistors for the rear panel power indicator LEDs, have 0805 footprint rather than 1206.
4. When I drew up the PCB, R23, the 4kohm resistor in the R-C-R network, was set up as a 1W resistor. Let's say there can be 15 mA flowing through this resistor - the power dissipated is 15e-3 ^2 * 4e3 is 0.9W, which is uncomfortably close to the limit. For all the tests above, I used a 3W resistor, and didn't find any serious noise issues. The drilled holes are a little tight for this higher power rated resistor, but I don't think this is a showstopper.

Communications with Apex:

I've been talking to support at Apex, and pointed out that I couldn't match the SPICE model performance even for a simple non-inverting amplifier with the PA95. The feedback I got from them was that

1. They don't optimize the SPICE models for input noise and so it was a nice coincidence that model and measurement are somewhat close (but not exactly).
2. They recommend the PA194, which is actually advertised as "low-noise". The PA95 is apparently not a "low-noise" part, with its 2uVrms input noise.

Whiel the PA194 is compatible with our voltage and current requirements for this application, it is ~3x the cost, and seems like the R-C-R output filter allows us to realize the goal of 1pA/rtHz, so I'm inclined to stick with the PA95.

Production assembly:

I'd prefer to get as much of the board stuffed by Screaming Circuits as possible. It took me ~3 hours to stuff 1 channel + the power supply parts, standoffs etc. So I estimate it'll take me ~6 hours to stuff the entire board. So not the end of the world if we have to do it in-house.

Attachment 1: inputDiffRecTF.pdf
Attachment 2: LVnoises.pdf
Attachment 3: totalNoise.pdf
Attachment 4: timeDomainTests.pdf
15815   Thu Feb 18 03:20:09 2021 KojiSummaryElectronicsCurrent Rack Map

Attachment 1: rack_plan.pdf
15820   Thu Feb 18 20:24:48 2021 KojiSummaryElectronicsA bunch of electronics received

Todd provided us a bunch of electronics. I went to Downs to pick them up this afternoon and checked the contents in the box. Basically, the boxes are pretty comprehensive to produce the following chassis

• 8 HAM-A coil driver chassis
• 7 16bit Anti-Aliasing chassis
• 4 18bit Anti-Imaging chassis
• 5 16bit Anti-Imaging chassis

Some panels are missing (we cannibalized them for the WFS electronics). Otherwise, it seems that we will be able to assemble these chassis listed.
They have placed inside the lab as seen in the attached photo.

HAM-A COIL DRIVER (Req Qty 28+8)

- 8 Chassis
- 8 Front Panels
- 8 Rear Panels
- 8 HAM-A Driver PCBs
- 8 D1000217 DC Power board
- 8 D1000217 DC Power board

16bit AA (Req Qty 7)
- 7 CHASSIS
- 6 7 Front Panels (1 missing -> [Ed 2/22/2021] Asked Chub to order -> Received on 3/5/2021)
- 7 Rear Panels
- 28 AA/AI board S2001472-486, 499-511
- 7 D070100 ADC AA I/F
- 7 D1000217 DC Power board

18bit AI (Req Qty 4)
- 4 CHASSIS
- 4 Front Panels
- 4 Rear Panels
- 8 AA/AI board S2001463-67, 90-92
- 4 D1000551 18bit DAC AI I/F
- 4 D1000217 DC Power board
- bunch of excess components

16bit AI (Req Qty 5)
- 5 CHASSIS
- 4 5 Front Panels (D1101522) (1 missing -> [Ed 2/22/2021] Asked Chub to order -> Received on 3/5/2021)
- 3 5 Rear Panels (D0902784) (2 missing -> [Ed 2/22/2021] Asked Chub to order -> Received on 3/5/2021)
- 10 AA/AI board S2001468-71, 93-98
- 5 D1000217 DC Power board
- 5 D070101 DAC AI I/F

Internal Wiring Kit

[Ed 2/22/2021]
- Qty 12 1U Hamilton Chassis
- Qty 5 x Front/Rear Panels/Internal PCBs for D1002593 BIO I/F (The parts and connectors to be ordered separately)

-> Components ordered by KA (3/7/2021)

Attachment 1: IMG_0416.jpeg
15828   Sat Feb 20 10:01:48 2021 gautamSummaryElectronicsA bunch of electronics received

Will we also be receiving the additional 34 Satellite Amplifier PCBs?

15830   Sat Feb 20 16:46:17 2021 KojiSummaryElectronicsA bunch of electronics received

We received currently available sets. We are supposed to receive more coil drivers and sat amps, etc. But they are not ready yet.

15846   Fri Feb 26 16:31:02 2021 gautamUpdateElectronicsProduction version of the HV coil driver tested with KEPCO HV supplies

Koji asked me to test the production version of the coil driver with the KEPCO HV supplies. See Attachment #1 for the results. For comparison, I've added a single trace from the measurements made with the HP supplies. I continue to see excess noise with the KEPCO supplies. Note that in the production version of the board that was tested, there are a pair of 10uF bypass capacitors on the board for the HV supply lines. It is possible that one or both KEPCO supplies are damaged - one was from the ASY setup and one I found in the little rack next to 1X2. The test conditions were identical to that with the HP supplies (as best as I could make it so).

Attachment 1: totalNoise_KEPCO.pdf
15847   Fri Feb 26 20:20:43 2021 KojiUpdateElectronicsProduction version of the HV coil driver tested with KEPCO HV supplies

This is very disappointing. Even with KEPCO linear supply with the improved HV driver circuit, the noise level is significantly higher than the 20kOhm R thermal noise.

What is special with the HP supplies? Can you replace KEPCOs with the HP supply, one by one to specify which one is making the noise bad?

15848   Sat Feb 27 17:25:42 2021 gautamUpdateElectronicsProduction version of the HV coil driver tested with KEPCO HV supplies

I will try the test of switching out KEPCOs one at a time for the HP. Given that the passive RC filter doesn't filter out the excess, I am wondering if the KEPCO is somehow polluting the circuit ground? The measurement was made between the circuit side of R24 (see schematic) and a ground testpoint, so the passive R23/C15 pole should filter the noise above ~15 Hz.

 Quote: This is very disappointing. Even with KEPCO linear supply with the improved HV driver circuit, the noise level is significantly higher than the 20kOhm R thermal noise. What is special with the HP supplies? Can you replace KEPCOs with the HP supply, one by one to specify which one is making the noise bad?
15865   Thu Mar 4 23:57:35 2021 KojiSummaryElectronicsInspection of the new custom dsub cables

I made the inspection of the new custom DSub cables (came from Texas).

The shelled version gives us some chance to inspect/modify the internal connections. (good)
The wires are well insulated. The conductors are wrapped with the foils and then everything is in the braid tube shield. The braid is soldered on one of the connectors. (Attachment  3/4 shows the soldering of the conductor by intentionally removing one of the insulations).

It wasn't clear that if the conductors are twisted or not (probably not).

Attachment 1: 20210304235251_IMG_0527.jpg
Attachment 2: 20210304235302_IMG_0528.jpg
Attachment 3: 20210304235339_IMG_0529.jpg
Attachment 4: 20210305000050_IMG_0530.jpg
Attachment 5: 20210305000610_IMG_0531.jpg
Attachment 6: 20210305000615_IMG_0532.jpg
15866   Fri Mar 5 00:53:09 2021 KojiSummaryElectronicsA bunch of electronics received

15868   Fri Mar 5 15:03:28 2021 gautamSummaryElectronicsA bunch of electronics received

The PCBs for the D1002593 BIO I/F (5pcs ea of D1001050 and D1001266) were received (from JLCPCB) today. idk what the status of the parts (digikey?) is.

15870   Fri Mar 5 15:32:53 2021 KojiSummaryElectronicsA bunch of electronics received

The parts will be ordered by Koji The components for the additional BIO I/F have been ordered.

15885   Tue Mar 9 12:41:29 2021 KojiSummaryElectronicsInvestigation on the invacuum Dsub cables

I believe the aLIGO style invac dsub cables and the conventional 40m ones are incompatible.
While the aLIGO spec is that Pin1 (in-vac) is connected to the shield, Pin13 (in-vac) is the one for the conventional cable. I still have to check if Pin13 is really connected to the shield, but we had trouble before for the IO TTs https://nodus.ligo.caltech.edu:8081/40m/7864.
(At least one of the existing end cables did not show this Pin13-chamber connection. However, the cables OMC/IMC chambers indicated this feature. So the cables are already inhomogenious.)

- Which way do we want to go? Our electronics are updated with aLIGO spec (New Sat amp, OMC electronics, etc), so I think we should start making the shift to the aLIGO spec.

- Attachment Top: The new coil drivers can be used together with the old cables using a custom DB25 cable (in-air).

- Attachment Mid: The combination of the conventional OSEM wiring and the aLIGO in-vac cable cause the conflict. The pin1 which is connected to the shield is used for the PD bias.

- Attachment Bottom: This can be solved by shifting the OSEMs by one pin.

Notes:
o The aLIGO cables have 12 twisted pair wires, but paired signals do not share a twisted pair.
--- No. This can't be solved by rotating the connectors.
o This modification should be done only for the new suspension.
--- In principle, we can apply this change to any SOSs. However, this action involves the vent. We probably want to install the new electronics for the existing suspensions before the vent.
o ^- This means that we have to have two types of custom DB25 in-air cables.
--- Each cable should handle "Shield wire" from the sat amp correctly.

Active TT Pin Issue
https://nodus.ligo.caltech.edu:8081/40m/7863

Hacky solution
https://nodus.ligo.caltech.edu:8081/40m/7869

Photo
Active TT Pin Swapping (December 21, 2012)

TT Wiring Diagram (Wiki)
https://wiki-40m.ligo.caltech.edu/Suspensions/Tip_Tilts_IO

Attachment 1: SOS_OSEM_cabling.pdf
15933   Wed Mar 17 15:04:20 2021 gautamUpdateElectronicsRibbon cable for chassis

I had asked Chub to order 100ft ea of 9, 15 and 25 conductor ribbon cable. These arrived today and are stored in the VEA alongside the rest of the electronics/chassis awaiting assembly.

Attachment 1: IMG_9139.jpg
15941   Thu Mar 18 18:06:36 2021 gautamUpdateElectronicsModified Sat Amp and Coil Driver

I uploaded the annotated schematics (to be more convenient than the noise analysis notes linked from the DCC page) for the HAM-A coil driver and Satellite Amplifier.

15950   Sun Mar 21 19:31:29 2021 ranaSummaryElectronicsRTL-SDR for monitoring RF noise / interference

When we're debugging our RF system, either due to weird demod phases, or low SNR, or non-stationary noise in the PDH signals, its good to have some baseline measurements of the RF levels in the lab.

I got this cheap USB dongle (RTL-SDR.COM) that seems to be capable of this and also has a bunch of open source code on GitHub to support it. It also comes mith an SMA coax and rabbit ear antenna with a flexi-tripod.

I used CubicSDR, which has free .dmg downloads for MacOS.It would be cool to have a student write some python code (perhaps starting with RTL_Power) for this to let us hop between the diffierent RF frequencies we care about and monitor the power in a small band around them.

15968   Thu Mar 25 18:05:04 2021 gautamUpdateElectronicsStuffed HV coil drivers received from Screaming Circuits

I think the only part missing for assembly now are 4 2U chassis. The PA95s need to be soldered on as well (they didn't arrive in time to send to SC). The stuffed boards are stored under my desk. I inspected one board, looks fine, but of course we will need to run some actual bench tests to be sure.

15980   Wed Mar 31 00:40:32 2021 KojiUpdateElectronicsElectronics Packaging for assembly work

I've worked on packing the components for the following chassis
- 5 16bit AI chassis
- 4 18bit AI chassis
- 7 16bit AA chassis
- 8 HAM-A coil driver chassis
They are "almost" ready for shipment. Almost means some small parts are missing. We can ship the boxes to the company while we wait for these small parts.

• DB9 Female Ribbon Receptacle AFL09B-ND Qty100 (We have 10) -> Received 90 on Apr 1st
• DB9 Male Ribbon Receptacle CMM09-G Qty100 (We have 10) -> Received 88 on Apr 1st
• 4-40 Pan Flat Head Screw (round head, Phillips) 1/2" long Qty 50 -> Found 4-40 3/8" Qty50 @WB EE on Apr 1st (Digikey H782-ND)
• Keystone Chassis Handle 9106 36-9106-ND Qty 50 -> Received 110 on Apr 1st
• Keystone Chassis Ferrule 9121 NKL PL 36-9121-ND Qty 100 -> Received 55 on Apr 1st
• Chassis Screws 4-40 3/16" Qty 1100 -> Received 1100 on Apr 1st
• Chassis Ear Screws 6-32 1/2" 91099A220 Qty 150 -> Received 400 of 3/8" on Apr 1st
• Chassis Handle Screws 6-32 1/4" 91099A205 Qty 100 -> included in the above
• Powerboard mounting screw 4-40 Pan Flat Head Screw (round head, Phillips) 1/4" long Qty 125 -> Received 100 on Apr 1st

And some more additional items to fill the emptying stock.

• 18AWG wires (we have orange/blue/black 1000ft, I'm sending ~1000ft black/green/white)
• Already consumed 80% of 100ft 9pin ribbon cable (=only 20ft left in the stock)
Attachment 1: P_20210330_233508.jpg
Attachment 2: P_20210330_233618.jpg
15981   Wed Mar 31 03:56:37 2021 KojiSummaryElectronicsA bunch of electronics received

Attachment 1: P_20210331_013257.jpg
Attachment 2: P_20210331_014020.jpg
15986   Thu Apr 1 18:16:28 2021 KojiUpdateElectronicsElectronics Packaging for assembly work

# All small components are packed in the boxes. They are ready to ship.

15990   Fri Apr 2 01:26:41 2021 gautamUpdateElectronicsREFL55 chain checkout again, seems fine

[koji, gautam]

Summary:

We could not find problems with any individual piece of the REFL55 electronics chain, from photodiode to ADC.  Nevertheless, the PRMI fringes witnessed by REFL55 is ~x10 higher than ~two weeks ago, when the PRMI could be repeatably and reliably locked using REFL55 signals (ETMs misaligned).

Details:

1. Koji prepared a spare whitening board. However, before he swapped it in, he checked the existing board and found no problems with it.
• 20mV input signal, 100 Hz was injected into the two REFL55 channels on the whitening board.
• The flat whitening gain was set to +45 dB.
• The signal levels seen in CDS was consistent with what is expected given an ADC conversion factor of 3276.8 cts/V.
2. Tried putting the REFL55 demodulated outputs into the next two channels, 5&6, (currently unused) on the same whitening board.
• After setting the whitening gains of these two channels also to +18dB, the saturation of the ADCs when the PRMI was fringing persisted.
3. With the dark noise of the whitening filter, we enabled/disabled the on board frequency dependent whitening, and reasoned that the time domain increase in RMS seemed reasonable. So we decided to investigate parts of the electronics chain upstream of the whitening board, since we couldn't find anything obviously wrong with the whitening board.
4. Injected -10dBm RF signal (=0.2 Vpp) into the RF input on the REFL55 demod board, and saw ~3500 cts-pp signal in CDS. This is totally consistent with my recent characterization of 16,000 cts/V for this demod board at the "nominal" + 18dB whitening gain setting. So the demodulator seems to function as advertised.
5. Decided to repeat my test of using the Jenne laser to test the whole chain end-to-end.
• In summary, we recovered the results (RF transimpedance of the PD, and signal levels in CDS for a known AM determined by the reference NF1611 PD) I reported there.
• So it would seem that the entire REFL55 electronics chain performs as expected.
• The only remaining explanation is that the optical gain of the PRMI has increased - but how??
• Similar jumps in the REFL55 signal levels have occurred multiple times in the past, and each time, I was able to recover the "nominal" performance by this procedure (though I have no idea why that should work at all).
• So I am highly skeptical that this has anything to do with the IFO optical gain, but that is the only difference between our AM laser based test and the "live" operating conditions when the signals are saturated.

Discussion and next steps:

Q: Koji asked me what is the problem with this apparent increased optical gain - can't we just compensate by decreasing the whitening gain?
A: I am unable to transition control of the PRMI (no ETMs) from 3f to 1f, even after reducing the whitening gain on the REFL55 channels to prevent the saturation. So I think we need to get to the bottom of whatever the problem is here.

Q: Why do we need to transfer the control of the vertex to the 1f signals at all?
A: I haven't got a plot in the elog, but from when I had the PRFPMI locked last year, the DARM noise between 100-1kHz had high coherence with the MICH control signal. I tried some feedforward to try and cancel it but never got anywhere. It isn't a quantitative statement but the 1f signals are expected to be cleaner?

Koji pointed out that the MICH signal is visible in the REFL55 channels even when the PRM is misaligned, so I'm gonna look back at the trend data to see if I can identify when this apparent increase in the signal levels occurred and if I can identify some event in the lab that caused it. We also discussed using the ratio of MICH signals in REFL and AS to better estimate the losses in the REFL path - the Faraday losses in particular are a total unknown, but in the AS path, there is less uncertainty since we know the SRM transmission quite precisely, and I guess the 6 output steering mirrors can be assumed to be R=99%.

16033   Wed Apr 14 23:55:34 2021 gautamUpdateElectronicsHV Coil driver assembly

I've occcupied the southernmost electronics bench for assembling the 4 production version HV coil driver chassis. I estimate it will take me 3 days, and have left a sign indicating as much. Once the chassis assembly is done, I will need to occupy the northernmost bench where bench supplies are to run some functionality tests / noise measurements, and so unless there are objections, I will move the Acromag box which has been sitting there.

16070   Thu Apr 22 01:42:38 2021 KojiSummaryElectronicsHV Supply Comparison

New HV power supply from Company 'M' has been delivered. So I decided to compare the noise levels of some HV supplies in the lab. There are three models from companies 'H', 'K', and 'M'.

The noise level was measured with SR785 via Gautam's HP filter with protection diodes.

'H' is a fully analog HV supply and the indicator is analog meters.
'K' is a model with a LCD digital display and numerical keypad.
'M' is a model with a knob and digital displays.

All the models showed that the noise levels increased with increased output voltage.

Among these three, H showed the lowest noise. (<~1uV/rtHz@10Hz and <50nV/rtHz@100Hz) (Attachment 1)

K is quite noisy all over the measured freq range and the level was <50uV/rtHz. Also the PSD has lots of 5Hz harmonics. (Attachment 2)

M has a modest noise level (<~30uV/rtHz@10Hz and <1uV/rtHz@100Hz)except for the noticeable line noise (ripple). (Attachment 3)

The comparison of the three models at 300V is Attachment 4. The other day Gautam and I checked the power spectrum of the HV coil driver with KEPCO and the output noise level of the coil driver was acceptable. So I expect that we will be able to use the HV supply from Company M. Next step is to check the HV driver noise with the model by M used as the supply.

Attachment 1: HV_Supply_PSD_H.pdf
Attachment 2: HV_Supply_PSD_K.pdf
Attachment 3: HV_Supply_PSD_M.pdf
Attachment 4: HV_Supply_PSD.pdf
16140   Fri May 14 03:29:50 2021 KojiUpdateElectronicsHV Driver noise test with the new HV power supply from Matsusada

I believe I did the identical test with the one in [40m ELOG 15786]. The + input of PA95 was shorted to the ground to exclude the noise from the bias input. The voltage noise at TP6 was measured with +/-300V supply by two HP6209 and two Matsusada R4G360.

With R4G360, the floor level was identical and 60Hz line peaks were less. It looks like R4G360 is cheap, easier and precise to handle, and sufficiently low noise.

Attachment 1: HV_Driver_PSD.pdf
16148   Thu May 20 16:56:21 2021 KojiUpdateElectronicsProduction version of the HV coil driver tested with KEPCO HV supplies

HP HV power supply ( HP6209 ) were returned to Downs

Attachment 1: P_20210520_154523_copy.jpg
16150   Fri May 21 00:15:33 2021 KojiUpdateElectronicsDC Power Strip delivered / stored

DC Power Strip Assemblies delivered and stored behind the Y arm tube (Attachment 1)

• 7x 18V Power Strip (Attachment 2)
• 7x 24V Power Strip (Attachment 2)
• 7x 18V/24V Sequencer / 14x Mounting Panel (Attachment 3)
• DC Power Cables 3ft, 6ft, 10ft (Attachments 4/5)
• DC Power Cables AWG12 Orange / Yellow (Attachments 6/7)

I also moved the spare 1U Chassis to the same place.

• 5+7+9 = 21x 1U Chassis (Attachments 8/9)

Attachment 1: P_20210520_233112.jpeg
Attachment 2: P_20210520_233123.jpg
Attachment 3: P_20210520_233207.jpg
Attachment 4: P_20210520_231542.jpg
Attachment 5: P_20210520_231815.jpg
Attachment 6: P_20210520_195318.jpg
Attachment 7: P_20210520_231644.jpg
Attachment 8: P_20210520_233203.jpg
Attachment 9: P_20210520_195204.jpg
16155   Mon May 24 08:38:26 2021 ChubUpdateElectronics18-bit AI, 16-bit AI and 16-bit AA

- High priority units: 2x 18AI / 1x 16AI / 3x 16AA

All six are reworked and on the electronics workbench. The rest should be ready by the end of the week.

Chub

16160   Tue May 25 17:08:17 2021 ChubUpdateElectronicschassis rework complete!

All remaining chasses have been reworked and placed on the floor along the west wall in Room 104.

Attachment 1: 40M_chassis_reworked_5-25-21.jpg
16162   Wed May 26 02:00:44 2021 gautamUpdateElectronicsCoil driver noise

I was preparing a short write-up / test procedure for the custom HV coil driver, when I thought of something I can't resolve. I'm probably missing some really basic physics here - but why do we not account for the shot noise from DC current flowing through the series resistor? For a 4kohm resistor, the Johnson current noise is ~2pA/rtHz. This is the target we were trying to beat with our custom designed HV bias circuit. But if there is a 1 mA DC current flowing through this resistor, the shot noise of this current is $\sqrt{2eI_{\mathrm{DC}}} \approx$18pA/rtHz, which is ~9 times larger than the Johnson noise of the same resistor. One could question the applicability of this formula to calculate the shot noise of a DC current through a wire-wound resistor - e.g. maybe the electron transport is not really "ballistic", and so the assumption that the electrons transported through it are independent and non-interacting isn't valid. There are some modified formulae for the shot noise through a metal resistor, which evaluates to $\sqrt{2eI_{\mathrm{DC}}/3} \approx$10pA/rtHz for the same 4kohm resistor, which is still ~5x the Johnson noise.

In the case of the HV coil driver circuit, the passive filtering stage I added at the output to filter out the excess PA95 noise unwittingly helps us - the pole at ~0.7 Hz filters the shot noise (but not the Johnson noise) such that at ~10 Hz, the Johnson noise does indeed dominate the total contribution. So, for this circuit, I think we don't have to worry about some un-budgeted noise. However, I am concerned about the fast actuation path - we were all along assuming that this path would be dominated by the Johnson noise of the 4kohm series resistor. But if we need even 1mA of current to null some DC DARM drift, then we'd have the shot noise contribution become comparable, or even dominant?

I looked through the iLIGO literature, where single-stage suspensions were being used, e.g. Rana's manifesto, but I cannot find any mention of shot noise due to DC current, so probably there is a simple explanation why - but it eludes me, at least for the moment. The iLIGO coil drivers did not have a passive filter at the output of the coil driver circuit (at least, not till this work), and there isn't any feedback gain for the DARM loop at >100 Hz (where we hope to measure squeezing) to significantly squash this noise.

Attachment #1 shows schematic topologies of the iLIGO and proposed 40m configs. It may be that I have completely misunderstood the iLIGO config and what I've drawn there is wrong. Since we are mainly interested in the noise from the resistor, I've assumed everything upstream of the final op-amp is noiseless (equivalently, we assume we can sufficiently pre-filter these noises).
Attachment #2 shows the relative magnitudes of shot noise due to a DC current, and thermal noise of the series resistor, as a function of frequency, for a few representative currents, for the slow bias path assuming a 0.7Hz corner from the 4kohm/3uF RC filter at the output of the PA95.

Some lit review suggests that it's actually pretty hard to measure shot noise in a resistor - so I'm guessing that's what it is, the mean free path of electrons is short compared to the length of the resistor such that the assumption that electrons arrive independently and randomly isn't valid. So Ohm's law dictates $I=V/R$ and that's what sets the current noise. See, for example, pg 432 of Horowitz and Hill.

Attachment 1: coilDriverTopologies.pdf
Attachment 2: shotVthermal.pdf
16211   Thu Jun 17 22:19:12 2021 KojiUpdateElectronics25 HAM-A coil driver units delivered

25 HAM-A coil driver units were fabricated by Todd and I've transported them to the 40m.
The last (1) unit has been completed, but Luis wants to use it for some A+ testing. So 1 more unit is coming.

Attachment 1: P_20210617_195811.jpg
16349   Mon Sep 20 20:43:38 2021 TegaUpdateElectronicsSat Amp modifications

Running update of Sat Amp modification work, which involves the following procedure (x8) per unit:

1. Replace R20 & R24 with 4.99K ohms, R23 with 499 ohms, and remove C16.
2. (Testing) Connect LEDDrive output to GND and check that
• TP4 is ~ 5V
•  TP5-8 ~ 0V.
3. Install 40m Satellite to Flange Adapter (D2100148-v1)

 Unit Serial Number Issues Status S1200740 NONE DONE S1200742 NONE DONE S1200743 NONE DONE S1200744 TP4 @ LED1,2 on PCB S2100568 is 13V instead of 5V TP4 @ LED4 on PCB S2100559 is 13V instead of 5V DONE S1200752 NONE DONE

Attachment 1: IMG_20210920_203456226.jpg
16356   Wed Sep 22 17:22:59 2021 TegaUpdateElectronicsSat Amp modifications

[Koji, Tega]

Decided to do a quick check of the remaining Sat Amp units before component replacement to identify any unit with defective LED circuits. Managed to examine 5 out of 10 units, so still have 5 units remaining. Also installed the photodiode bias voltage jumper (JP1) on all the units processed so far.

Unit Serial Number Issues Debugging Status
S1200738

TP4 @ LED3 on chan 1-4 PCB was ~0.7 V instead of 5V

Koji checked the solder connections of the various components, then swapped out the IC OPAMP. Removed DB9 connections to the front panel to get access to the bottom of the board. Upon close inspection, it looked like an issue of a short connection between the Emitter & Base legs of the Q1 transistor.

Solution - Remove the short connection between the Emitter & Base legs of the Q1 transistor legs.

DONE
S1200748 TP4 @ LED2 on chan 1-4 PCB was ~0.7 V instead of 5V

This issue was caused by a short connection between the Emitter & Base legs of the Q1 transistor.

Solution - Remove the short connection between the Emitter & Base legs of the Q1 transistor legs.

DONE
S1200749 NONE N/A DONE
S1200750 NONE N/A DONE
S1200751 NONE N/A DONE

Defective unit with updated resistors and capacitors in the previous elog

Unit Serial Number Issues Debugging Status
S1200744

TP4 @ LED1,2 on PCB S2100568 is 13V instead of 5V

TP4 @ LED4 on PCB S2100559 is 13V instead of 5V

This issue was caused by a short between the Collector & Base legs of the Q1 transistor.

Solution - Remove the short connection between the Collector & Base legs of the Q1 transistor legs

Complications - During the process of flipping the board to get access to the bottom of the board, a connector holding the two middle black wires, on P1, came loose. I resecured the wires to the connector and checked all TP4s on the board afterwards to make sure things are as expected.

DONE

Quote:

Running update of Sat Amp modification work, which involves the following procedure (x8) per unit:

1. Replace R20 & R24 with 4.99K ohms, R23 with 499 ohms, and remove C16.
2. (Testing) Connect LEDDrive output to GND and check that
• TP4 is ~ 5V
•  TP5-8 ~ 0V.
3. Install 40m Satellite to Flange Adapter (D2100148-v1)

 Unit Serial Number Issues Status S1200740 NONE DONE S1200742 NONE DONE S1200743 NONE DONE S1200744 TP4 @ LED1,2 on PCB S2100568 is 13V instead of 5V TP4 @ LED4 on PCB S2100559 is 13V instead of 5V DONE S1200752 NONE DONE

16357   Thu Sep 23 14:17:44 2021 TegaUpdateElectronicsSat Amp modifications debugging update

Debugging complete.

All units now have the correct TP4 voltage reading needed to drive a nominal current of 35 mA through to OSEM LED. The next step is to go ahead and replace the components and test afterward that everything is OK.

Unit Serial Number Issues Debugging Status
S1200736 TP4 @ LED4 on chan 1-4 PCB reads 13V instead of 5V

This issue was caused by a short between the Collector & Base legs of the Q1 transistor.

Solution - Remove the short connection between the Collector & Base legs of the Q1 transistor legs

DONE
S1200737 NONE N/A DONE
S1200739 NONE N/A DONE
S1200746 TP4 @ LED3 on chan 5-8 PCB reads 0.765 V instead of 5V

This issue was caused by a short between the Emitter & Base legs of the Q1 transistor.

Solution - Remove the short connection between the Emitter & Base legs of the Q1 transistor legs

Complications - I was extra careful this time because of the problem of loose cable from the last flip-over of the right PCB containing chan 5-8. Anyways, after I was done I noticed one of the pink wires (it carries the +14V to the left PCB) had come off on P1. At least this time I could also see that the corresponding front panel green LED turn off as a result. So I resecured the wire to the connector (using solder as my last attempt yesterday to reattach the via crimping didn't work after a long time trying. I hope this is not a problem.) and checked the front panel LED turns on when the unit is powered before closing the unit. These connectors are quite flimsy.

DONE
S1200747 TP4 @ LED2 on chan 1-4 PCB reads 13V instead of 5V

This issue was caused by a short between the Collector & Base legs of the Q1 transistor.

Solution - Remove the short connection between the Collector & Base legs of the Q1 transistor legs

DONE

16377   Mon Oct 4 18:35:12 2021 PacoUpdateElectronicsSatellite amp box adapters

[Paco]

I have finished assembling the 1U adapters from 8 to 5 DB9 conn. for the satellite amp boxes. One thing I had to "hack" was the corners of the front panel end of the PCB. Because the PCB was a bit too wide, it wasn't really flush against the front panel (see Attachment #1), so I just filed the corners by ~ 3 mm and covered with kapton tape to prevent contact between ground planes and the chassis. After this, I made DB9 cables, connected everything in place and attached to the rear panel (Attachment #2). Four units are resting near the CAD machine (next to the bench area), see Attachment #3.

Attachment 1: pcb_no_flush.jpg
Attachment 2: 1U_assembly.jpg
Attachment 3: fourunits.jpg
16378   Mon Oct 4 20:46:08 2021 KojiUpdateElectronicsSatellite amp box adapters

Thanks. You should be able to find the chassis-related hardware on the left side of the benchtop drawers at the middle workbench.

Hardware: The special low profile 4-40 standoff screw / 1U handles / screws and washers for the chassis / flat-top screws for chassis panels and lids

16379   Mon Oct 4 21:58:17 2021 TegaUpdateElectronicsSat Amp modifications

Trying to finish 2 more Sat Amp units so that we have the 7 units needed for the X-arm install.

S2100736 - All good

S2100737 - This unit presented with an issue on the PD1 circuit of channel 1-4 PCB where the voltage reading on TP6, TP7 and TP8 are -15.1V,  -14.2V, and +14.7V respectively, instead of ~0V.  The unit also has an issue on the PD2 circuit of channel 1-4 PCB because the voltage reading on TP7 and TP8 are  -14.2V, and +14.25V respectively, instead of ~0V.

16380   Tue Oct 5 17:01:20 2021 KojiUpdateElectronicsSat Amp modifications

Make sure the inputs for the PD amps are open. This is the current amplifier and we want to leave the input pins open for the test of this circuit.

TP6 is the first stage of the amps (TIA). So this stage has the issue. Usual check if the power is properly supplied / if the pins are properly connected/isolated / If the opamp is alive or not.

For TP8, if TP8 get railed. TP5 and TP7 are going to be railed too. Is that the case, if so, check this whitening stage in the same way as above.
If the problem is only in the TP5 and/or TP7 it is the differential driver issue. Check the final stage as above. Replacing the opamp could help.

16386   Wed Oct 6 16:31:02 2021 TegaUpdateElectronicsSat Amp modifications

[Tega, Koji]

(S2100737) - Debugging showed that the opamp, AD822ARZ, for PD2 circuit was not working as expected so we replaced with a spare and this fixed the problem. Somehow, the PD1 circuit no longer presents any issues, so everything is now fine with the unit.

(S2100741) - All good.

 Quote: Trying to finish 2 more Sat Amp units so that we have the 7 units needed for the X-arm install.  S2100736 - All good S2100737 - This unit presented with an issue on the PD1 circuit of channel 1-4 PCB where the voltage reading on TP6, TP7 and TP8 are -15.1V,  -14.2V, and +14.7V respectively, instead of ~0V.  The unit also has an issue on the PD2 circuit of channel 1-4 PCB because the voltage reading on TP7 and TP8 are  -14.2V, and +14.25V respectively, instead of ~0V.

16387   Thu Oct 7 02:04:19 2021 KojiUpdateElectronicsSatellite amp adapter chassis

The 4 units of Satellite Amp Adapter were done:
- The ears were fixed with the screws
- The handles were attached (The stock of the handles is low)
- The boards are now supported by plastic stand-offs. (The chassis were drilled)
- The front and rear panels were fixed to the chassis
- The front and rear connectors were fixed with the low profile 4-40 stand-off screws (3M 3341-1S)

Attachment 1: P_20211006_205044.jpg
16411   Mon Oct 18 16:48:32 2021 TegaUpdateElectronicsSat Amp modifications

[S2100738, S2100745, S2100751] Completed three more Sat Amp units modification with seven remaining.

Attachment 1: IMG_20211018_162918574.jpg
16427   Tue Oct 26 13:27:07 2021 TegaSummaryElectronicsSat Amp modification Summary

Modifications and testing of SatAmp units COMPLETE. Attachments 1 & 2 show all 19 units, one installed unit and the remaining 18 units are stacked and ready for install. Detailed notes of the modification for each unit are presented in the summary document in the dcc.

Attachment 1: SapAmpModStack.jpg
Attachment 2: SatAmpInstalled.jpg
16428   Tue Oct 26 14:53:24 2021 KojiUpdateElectronicsRack

1. We have a rack at the 40m storage. We are free to take it to the lab. If there is a tag, tell the info to Liz. Let's move it to the lab tomorrow right after the meeting.

2. We have a few racks in WB B1 (Attachment 1). Liz and I checked a rack which looks suitable for us. 46U height. Caltech transport will move it to the lab.

Attachment 1: P_20211026_143814.jpg
16436   Wed Oct 27 19:34:52 2021 KojiSummaryElectronicsNew electronics racks

1. The rack we cleaned today (came from West Bridge) will be placed between 1X3 and 1X4, right next to 1X4 (after removing the plastic boxes). (Attachment 1)
For easier work at the side of the 1X4, the side panel of the 1X4 should be removed before placing the new rack. Note that this rack is imperial and has 10-32 threads

2. In terms of the other rack for the Y arm, we found the rack in the storage is quite dirty. Anchal pointed out that we have a few racks standing along the Y arm (as the storage of the old VME/Euro card electronics) (Attachments 2/3)
They are not too dirty and also doing nothing there. Let's vacate one of them (the one right next to the optics preparation table). Use this space as a new storage area placing a wire shelving rack for something.

BTW, I thought it is good to have the rack at the vertex side of 1Y1 (as 1Y0?), but the floor has "KEEP OUT" marking. I have no idea why we have this marking. Is this for crane operation??? Does any one know?

Attachment 1: P_20211027_180737.jpg
Attachment 2: P_20211027_180443.jpg
Attachment 3: P_20211027_180408.jpg
Attachment 4: P_20211027_180139.jpg
16513   Thu Dec 16 15:04:12 2021 ChubUpdateElectronicsITMX feedthroughs and in-vac cables installed

The ITMX 10" flange with four DSUB-25 feedthroughs has been install with the cables connected at the in-vac side.  See photo; as requested, LO1-1 and LO1-2 are connected to the top row of feedthroughs from left to right respectively and the opposite ends of the cables placed left to right on the laser table.  PR2-1 and PR2-2 are connected to the lower row of feedthroughs from left to right respectively, with the opposite ends placed on the surface below the laser from left to right.  This seemed the easiest way to keep the cable orientation clear.

Attachment 1: ITMX_feedthrough_install_12-16-21.jpg
16515   Thu Dec 16 15:54:08 2021 KojiUpdateElectronicsITMX feedthroughs and in-vac cables installed

Thanks for the installation.

With regard to the connector convention, let's use the attached arrangement so that it will be consistent with the existing flange DSUB configuration. Not a big deal.

Attachment 1: PXL_20211216_235056582.jpg
16530   Tue Dec 21 16:52:39 2021 AnchalSummaryElectronicsIn-air Sat Amp to Vacuum Flange cables laid for 7 new SOS

[Anchal, Yehonathan, Chub]

We today laid down 14 70 ft long DB25 cables from 1Y1 (6), 1Y0 (8) to ITMY Chamber (4), BS Chamber (6) and ITMX Chamber (4). The cables have been connected to respective satellite amplifier on the racks and the other ends are connected to the vacuum flange feedthru on ITMX for LO1 and PR2, while the others have been kept near the planned flange postions. LO1 is now ready to be connected to CDS by connecting the in-vacuum cable inside ITMX chamber to the OSEMs.

16563   Mon Jan 10 15:45:55 2022 PacoUpdateElectronicsITMY feedthroughs and in-vac cables installed - part I

The ITMY 10" flange with 10 DSUB-25 feedthroughs has been installed with the cables connected at the in-vac side.  This is the first of two flanges, and includes 5 cables ordered vertically in stacks of 3 & 2 for [[OMC-DCPDs, OMC-QPDs, OMC-PZTs/Pico]] and [[SRM1, SRM2]] respectively from right to left. During installation, two 12-point silver plated bolts were stripped, so Chub had to replace them.

16569   Tue Jan 11 10:23:18 2022 PacoUpdateElectronicsITMY feedthroughs and in-vac cables installed - part II

[Paco, Chub]

The ITMY 10" flange with 4 DSUB-25 feedthroughs has been installed with the cables connected at the in-vac side. This is the second of two flanges, and includes 4 cables ordered vertically in stacks of 2 & 2 for [[AS1-1, AS1-2, AS4-1, AS4-2]] respectively. No major incidents during this one, except maybe a note that all the bolts were extremely dirty and covered with gunk, so we gave a quick swipe with wet cloths before reinstalling them.

16574   Tue Jan 11 14:21:53 2022 PacoUpdateElectronicsBS feedthroughs and in-vac cables installed

[Paco, Yehonathan, Chub]

The BS chamber 10" flange with 4 DSUB-25 feedthroughs has been installed with the cables connected at the in-vac side. This is the second of two flanges, and includes 4 cables ordered vertically in stacks of 2 & 2 for [[LO2-1, LO2-2, PR3-1, PR3-2]] respectively.

16586   Fri Jan 14 12:01:21 2022 AnchalUpdateElectronicsBS & ITMY feedthroughs labeled and connected to Sat Amps

I labeled all the newly installed flanges and connected the in-air cables (40m/16530) to appropriate ports. These cables are connected to the CDS system on 1Y1/1Y0 racks through the satellite amplifiers. So all new optics now can be damped as soon as they are placed. We need to make more DB9 plugs for setting "Acquire" mode on the HAM-A coil drivers since our Binary input system is not ready yet. Right now, we only have 2 such plugs which means only one optic and be damped at a time.

ELOG V3.1.3-