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ID Date Author Type Category Subject
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
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

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.

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
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

12468   Fri Sep 2 21:16:45 2016 ranaUpdateElectronicsSatellite Amplifier

In November of 2010, Valera Frolov (LLO), investigated our satellite amplifiers and made some recommendations about how to increase the SNR.

In light of the recent issues, we ought to fix up one of the spares into this state and swap it in for the ITMY's funky box.

The sat amp schematic is (D961289). It has several versions. Our spare is labeled as version D (not a choice on the DCC page).

1. U13-17 seem superfluous. Why would we need a high current buffer to drive the slow EPICS ADCs ?
2. The Radd resistors indicated on the B2 schematic have not been added to this board. What would be the purpose of adding them anyway?
3. The transimpedance resistors are, in fact, 29.4k as indicated on the B1 schematic.
4. The LT1125: V_n = 3 nV w/ f_corner = 5 Hz. I_n = 0.4 pA w/ f_corner = 100 Hz. So at 1 Hz the current noise is limiting at ~120 nV/rHz or 650 nV/rHz using the 161k that Valera recommends.
5. Even in that case the ADC noise is higher than the opamp noise.
6. We should be using metal film resistors instead of the thick film junk that's installed now.

Edit (Sep 6): The purpose of the Radd resistors is to lower the resistance and thus up the current through the LED. The equivalent load becomes 287 Ohms. Presumably, this in series with the LED is what gives the 25 mA stated on the schematic. This implies the LED has an effective resistance of 100 Ohms at this operating point. Why 3 resistors? To distribute the heat load. The 1206 SMD resistors are usually rated for 1/4 W. Better to replace with 287 Ohm metal film resistors rated for 1 W, if Steve can find them online.

12470   Mon Sep 5 21:05:06 2016 ranaUpdateElectronicsSatellite Amplifier

The attached PDF shows the output noise of the satellite amp. This was calculated using 'osempd.fil' in the 40m/LISO GitLab repo.

The mean voltage output is ~1 Vdc, which corresponds to a current with a shot noise level of 100 nV/rHz on this plot. So the opamp current noise dominates below 1 Hz as long as the OSEM LED output is indeed quantum limited down to 0.1 Hz. Sounds highly implausible.

To convert into meters, we divide by the OSEM conversion factor of ~1.6 V/mm, so the shot noise equivalent would be ~1e-10 m/rHz above 1 Hz.

After adding the sat amp to the 40m DCC tree (D1600348), I notice that not only is the PD readout not built for low noise, neither is the LED drive.  The noise should be dominated by the voltage noise of the LT1031 voltage reference. This has a noise of ~500 nV/rHz at 1 Hz. That corresponds to an equivalent current noise through the LED of 25 mA * (500e-9 / 10) ~ 1 nA/rHz. Or ~45 nV/rHz at the sat amp output. This would be OK as long as everything behaves ideally. BUT, we have thick film (i.e. black surface mount) resistors on the LED drive so we'll have to measure it to make sure.

Also, why is the OSEM LED included in the feedback loop of the driver? It means disconnecting the cable from the sat amp makes the driver go unstable probably. I think one concept is that including the device in the feedback loop makes it so that any EMI picked up in the cabling, etc. gets cancelled out by the opamp. But this then requires that we test each driver to make sure it doesn't oscillate when driving the long cable.

If we have some data with one of the optics clamped and the open light hitting the PD, or with the OSEMs removed and sitting on the table, that would be useful for evaluating the end-to-end noise of the OSEM circuit. It seems like we probably have that due to the vent work, so please post the times here if you have them.

Attachment 1: osempd.pdf
12471   Tue Sep 6 00:14:14 2016 gautamUpdateElectronicsSatellite Amplifier

 If we have some data with one of the optics clamped and the open light hitting the PD, or with the OSEMs removed and sitting on the table, that would be useful for evaluating the end-to-end noise of the OSEM circuit. It seems like we probably have that due to the vent work, so please post the times here if you have them.

The ETMX OSEMs have been attached to its Satellite box and plugged in for the last 10 days or so, with the PD exposed to the unobstructed LED. I pulled the spectrum of one of the sensors (mean detrended, I assume this takes care of removing the DC value?). The DQed channels claim to record um (the raw ADC counts are multiplied by a conversion factor of 0.36). For comparison, re-converted the y-axis for the measured curve to counts, and multiplied the total noise curve from the LISO simulation by a factor of 3267.8cts/V (2^16cts/20V) so the Y axis is noise in units of counts/rtHz. At 1Hz, there is more than an order of magnitude difference between the simulation and the measurement which makes me suspect my y-axis conversion, but I think I've done this correctly. Can such a large discrepancy be solely due to thick film resistors?

Attachment 1: osempdComparison.pdf
12505   Mon Sep 19 13:25:03 2016 TengUpdateElectronicsSatellite Amplifier

In order to figure out the difference betweent simulated result and measurement, I tried to measuren the electronic noise by following ways as show in attachment 1

1.measure from the satellite box by SR785 at ETMY ,calibrate to counts by divide by 3267.8. while at that conditin, the set up is in suspension.

2. measure after ADC by diagnostics test tools, with set up on table in history and on uspension currently.

3. use the caculated butterfly channel.

the results are shown in attachmemt 2. The overall nosie level are still much higher than simulation.

Quote:

 If we have some data with one of the optics clamped and the open light hitting the PD, or with the OSEMs removed and sitting on the table, that would be useful for evaluating the end-to-end noise of the OSEM circuit. It seems like we probably have that due to the vent work, so please post the times here if you have them.

The ETMX OSEMs have been attached to its Satellite box and plugged in for the last 10 days or so, with the PD exposed to the unobstructed LED. I pulled the spectrum of one of the sensors (mean detrended, I assume this takes care of removing the DC value?). The DQed channels claim to record um (the raw ADC counts are multiplied by a conversion factor of 0.36). For comparison, re-converted the y-axis for the measured curve to counts, and multiplied the total noise curve from the LISO simulation by a factor of 3267.8cts/V (2^16cts/20V) so the Y axis is noise in units of counts/rtHz. At 1Hz, there is more than an order of magnitude difference between the simulation and the measurement which makes me suspect my y-axis conversion, but I think I've done this correctly. Can such a large discrepancy be solely due to thick film resistors?

15799   Wed Feb 10 15:07:50 2021 AnchalSummaryBHDSatellite Amplifier Output Offset measurements

I measured the output DC voltage of the satellite amplifier box at PDMon port when the PDA input was shorted and got following offsets:

CH Output Offset (mV) CH Output Offset (mV)
1 6 5 750
2 140 6 120
3 350 7 537
4 40 8 670

However, I think I'm making a mistake while measuring this offset as well as all the noise measurements of this satellite amplifier box so far. Since it is a current input, transimpedance circuit, the noise of the circuit should be measured with open input, not closed. Infact, by shorting the PDA input, I'm giving DC path to input bias current of AD833 transimpedance amplifier to create this huge DC offset. This won't be the case when a photodiode is connected at the input which is a capacitor and hence no DC path is allowed. So my issue of offset was bogus and past two noise measurements in 40m/15797 and 40m/15793 are wrong.

15800   Wed Feb 10 15:25:45 2021 gautamSummaryBHDSatellite Amplifier Output Offset measurements

Why not just do this test with the dummy suspension box and CDS system? I think Rich's claim was that the intrinsic LED RIN was dominant over any drive current noise but we can at least measure the quadrature sum of the two (which is after all the relevant quantity in terms of what performance we can realize) and compare to a model.

15801   Wed Feb 10 17:18:03 2021 KojiSummaryBHDSatellite Amplifier Output Offset measurements

Testing the satellite amp i.e.  PD driver
- To test the noise of the PD transimpedance amps:
Leave the PD input open (do not short the terminal goes to the PD)
- To test the current noise of the LED drivers: Short the output with an appropriate Rs to have the nominal current.
- To test the overall noise level together with the LED/PD pair: Connect the dummy OSEM module.

Testing the coil drivers
-
Short the output with an appropriate Rs.

15776   Mon Jan 25 18:18:04 2021 AnchalSummaryBHDSatellite Amplifier Transfer Functions and noise

I took transfer function and noise measurement of satellite amplifier box's photodiode transimpedance circuit. For the measurement, I created a makeshift connector to convert backside DB25 into DB9 with the 4 channels for PDA input. The output was taken in differential form at the front PD Output port. To feed current to the circuit, I put in 12 kOhm resistors in series at the inputs, so the V/V transfer function measured was multiplied by 12 kOhm to get the transimpedance of the circuit.

# Transfer Function Measurement details

• SR785 source out was fed into PDA input pins using a makeshift BNC-DB9-DB25 converter.
• The output from PDOut DB9 port was fed to test switch in D1900068 to separate differential signal.
• This differential signal was fed back to SR785 at input 2 in A-B configuration.
• Measurements are taken with file D1002818_TF.yml and D1002818_TF_LF.yml.
• A measurement of just cables without the DUT is taken as well.
• Commands.txt list all the commands used.
• All data is compiled and plotted in Plotting.ipynb
• D1100117_S2100029_TFandNoiseSpectrum.pdf shows all the transfer functions measured.

# Spectrum Measurements

• Two pair of BNC cables were twisted together and clips were added at ends.
• One of the GND was connected to board GND. Rest were left unconnected to avoid ground loops.
• Each pair of signal was connected to PDOutP/N.
• The PDA inputs were shorted together to make zero input current to the board.
• Instrument noise with cables was measured by shorting the clips of the center cores and one of the shields of the two BNC cables together.
• Measurements were taken with file D1002818_SP.yml and D1002818_SP_LF.yml.
• Input referred current noise spectrum was calculated by dividing the output voltage noise spectrum by the measured transfer function.
• D1100117_S2100029_TFandNoiseSpectrum.pdf shows all the output votlage noise spectrum and input referred current noise spectrum measured.

Edit Wed Feb 10 15:14:13 2021 :

THE NOISE MEASUREMENT WAS WRONG HERE. SEE 40m/15799.

Attachment 1: D1002818_S2100029_TFandNoiseSpectrum.pdf
Attachment 2: D1002818_Testing.zip
15793   Wed Feb 3 16:27:19 2021 AnchalSummaryBHDSatellite Amplifier Transfer Functions and noise After modifications

I have made modifications recommended in this doc. The changes made are:

• R24: 19.6k to 4.99k Ohms
• R20: 19.6k to 4.99k Ohms
• R23: 787 to 499 Ohms
• Removed C16.

I took transfer function measurements, fitted them with zeros and poles and plotted it against the zero model of the circuit. The zeros and poles we intended to shift are matching well with 3Hz zero and 30 Hz pole. The later pole at 1500 Hz is at a higher value from what is predicted by zero.

I also took noise measurements and they are in good agreement with the noise predicted by zero.

Edit Wed Feb 10 15:14:13 2021 :

THE NOISE MEASUREMENT WAS WRONG HERE. SEE 40m/15799.

Attachment 1: D1002818_S2100029_TFAfterChanges.pdf
Attachment 2: D1002818_S2100029_OutputNoiseSpecAfterChanges.pdf
Attachment 3: D1002818_S2100029_InputRefferedNoiseSpecAfterChanges.pdf
Attachment 4: D1002812_S2100029_After_Modifications_Feb3.jpg
Attachment 5: AfterChanges.zip
15797   Wed Feb 10 11:45:59 2021 AnchalSummaryBHDSatellite Amplifier Very Low frequency noise After modifications

As suggested, I wrapped the satellite amplifier box D10028128 S2100029 in blanket and foam and took very low frequency spectrum starting from 32 mHz to 3 Hz. The results are attached along with stiched high frequency measurements from 40m/15793.

# Very Low Frequency Spectrum Measurement

• D1002818 S2100029 box was powered and covered in a foam blanket.
• Additionally, it was covered from all sides with foam to reduce wind and temperature effects on it.
• The rear panel DB25 connector was connected to a breakout board where pins od PDA input and GND were shorted, shorting the transimpedance circuit input.
• The output was read from PDMon DB9 output at front panel which was converted to 4 BNC channels using breakout board.
• Two channel noise was measured at once using D1002818_SP.yml parameter file.
• Instrument noise at all the used input ranges were measured separately by shorting the input of the BNC cables.

Edit Wed Feb 10 15:14:13 2021 :

THIS MEASUREMENT WAS WRONG. SEE 40m/15799.

Attachment 1: FrontsideLook.jpg
Attachment 2: BacksideLook.jpg
Attachment 3: InnerFoamBlanket.jpg
Attachment 4: D1002818_S2100029_OutputNoiseLFSpecAfterChanges.pdf
Attachment 5: D1002818_S2100029_InputRefCurrentNoiseLFSpecAfterChanges.pdf
Attachment 6: AfterChangesLFSpectrum.zip
15803   Thu Feb 11 11:10:05 2021 AnchalSummaryBHDSatellite Amplifier Very Low frequency noise After modifications

Here is a proper measurement for PD transimpedance amplifier circuit in the Satellite amplifier box D1002818 S2100029. The input from rear DB25 connector was left open and measurement was taken with AC coupling with correction by the AC coupling transfer function (Zero at 0, pole at 160 mHz). I have calculated the input referred displacement noise by calculating the conversion factor of OSEM in A/m. From 40m/12470, old conversion factor of OSEM to output of sat amplifier was 1.6 V/mm. then, the transimpedance was 39.2 kOhm, so that must mean a conversion factor of 1.6e3/39.2 A/m. This I scaled with increased drive current by factor of 35/25 as mentioned in this document. The final conversion factor turned out to be around 57 mA / m. If someone finds error in this, please let me know.

There is excess noise in the low-frequency region below 5-6 Hz. If people think I should make a measurement of amplified noise to go further away from the instrument noise floor, let me know.

Attachment 1: AfterChangesSpectrum_AC.zip
Attachment 2: D1002818_S2100029_OutputNoiseSpecAfterChanges.pdf
Attachment 3: D1002818_S2100029_InputRefCurrentNoiseSpecAfterChanges.pdf
Attachment 4: D1002818_S2100029_InputRefDispNoiseSpecAfterChanges.pdf
15804   Thu Feb 11 16:58:52 2021 ranaSummaryBHDSatellite Amplifier Very Low frequency noise After modifications

I expect that a single OSEM channel can't be better than 1e-10 m/rHz above 5 Hz, so probably something wrong in the calibration. 1.6 V/mm seems right to me, so could be some place else.

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
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

14417   Thu Jan 24 22:55:50 2019 gautamUpdateElectronicsSatellite box S/N 102 investigation

I had taken Satellite box S/N 102, from the SRM suspension, down to the Y-end as part of debugging. However, at some point, I stopped getting readbacks from the shadow sensor PDs, even with the Sat. Box tester hooked up (so as to rule out anything funky with the actual OSEMs). Today evening, I did a more systematic investigation. Schematic with component references is here.

1. Used mini-grabbers and a bench power supply to connect +/-24V to C57 and C58.
2. Checked that all ICs were getting +/- 15 V to the supply pins.
3. Debugged individual channels, checking voltages at various nodes
• Found that the "PD K" bias voltage was anomalosly low.
• Found that the inverting input of U3C wasn't ground.
• The above findings are summarized in Attachment #2.
• This suggested something was wrong with the Quad OpAmp LT1125 IC, so I elected to switch it out.
• During the desoldering process, the pads for the "NC" pins came off (Attachment #1) - this has happened to me before on these old boards. I don't think I applied excess heat during the desoldering (I used 650F).
• Replaced the IC, and measured the expected 10V at the "PD K" node.
4. I then connected the tester box and verified all the shadow sensor channels (LED + PD) work as expected, using the front panel J3 and the "octopus cable".
5. It remains to verify that the coil driver signals get correctly routed through the Satellite box before giving this box a pass certification.

The question remains as to what caused this failure mode - I can't think of why that particular IC was damaged during the Satellite box swapping process - is this indicative of some problem elsewhere in the ETMY OSEM/coil driver electronics chain?

Attachment 1: IMG_7294.JPG
Attachment 2: D961289-B2.pdf
14421   Tue Jan 29 17:19:16 2019 gautamUpdateElectronicsSatellite box S/N 105 repaired

[chub, koji, gautam]

Attachment #1 shows the signal routing near the Satellite box. Somehow, the female 64 pin IDC connector that brings the signals from the coil driver board wasn't mating well with the mail connector on the Satellite box front panel. This is a connector specific problem - plugging the female end into one of the male connectors inside the Satellite box yielded signal continuity. The problem was resolved by re-making both connections -by driving the EPICS bias slider through its full range, we were able to see the full voltage swing at the DB connectors going to the flange

This kind of flakiness could be all around the lab, and could be responsible for many of the suspension "mysteries". To re-iterate, the problem seems to be the way the female sockets of the connector mates with the male pins - while the actual crimping points may look secure, there may not be signal continuity.

Now that this problem is resolved, tomorrow we will recover the cavity alignment and possibly start a pumpdown.

Unrelated to this work - the spare satellite box (S/N #100), which had a note on it that said "low voltages", was tested. The "low voltages" referred to the OSEM shadow sensor voltages being low when the LED was completely unobscured. The reason was that the mod to increase the drive current to 25 mA had not yet been implemented on this unit. I added the appropriate 806 ohm resistors, and verified that the voltages were correct, so now we have a working spare. It is stored in the "photodiode" cabinet along the east arm, together with the tester boxes.

Attachment 1: IMG_7301.JPG
1198   Sat Dec 20 23:37:43 2008 robOmnistructureGeneralSaturday Night Fever after presumed power failure

Just came by to pick something up...

... alarm handlers screeching...

... TP1 failure--closing V1... call Steve... Steve says ok till tomorrow...

... all front ends down (red)...

... all suspensions watchdogged...

... all (I think) servos off...

... PSL shutter closed ...

... chiller at 15C ... I turned it off to prevent condensation in PA...

... MOPA shutter closed... turned off key on Lightwave power supply

... good luck all, and happy holidays!
1495   Sun Apr 19 03:34:05 2009 YoichiUpdateLockingSaturday night lock
Tonight I was able to go up to arm power = 33, by mainly tweaking the DARM gain. A small progress.
In order to give more phase margin to the CARM MC_L path, I added a 300:100 filter to C1:LSC-MC.
To reduce the load to the lsc computer I deleted several filters from the filter bank, which were not used in the locking scripts.
Before I deleted the filters, I checked in the current chans directory into the svn repository.
If you want to restore the deleted filters, go back to the revision 36142.
16484   Wed Nov 24 14:34:15 2021 YehonathanUpdateBHDSaving on SUSAUX slow channels

Koji found out that the stock for BIO Acromag modules is very low and that the lead time for ordering new ones is ~ 1-year X-o.

We figure we might need to minimize the number of modules but still keep the Acromag chassis functional.

Looking at the new C1AUXEY feed-throughs spreadsheet one can see that we actually normally need only 1 BIO (not 2) module since there are 16 suspensions related bios + 1 green shutter which is unrelated to SUSAUX so there is no room to cut back here.

There are 16 analog input channels, 5 for PDMONs and 5 VMONs, and 6 spares which require 2 ADCs. Removing the spares and 2 monitoring channels will be enough to get us to 1 ADC.

10207   Tue Jul 15 22:23:51 2014 AndresUpdate40m Xend Table upgradeScan the Xarm for the mode matching

Nick and I with the help of Jenne scan the green light when the cavity is unlocked. Nick placed a Beam dump on the IR so that we can just scan the green, but it was removed as soon as we finished with the measurement. I'm working on the calculation, and i'll be posted solution tonight.

2499   Sun Jan 10 23:22:56 2010 JenneSummaryGeneralScattering Measurements of 35W Beam Dumps

On Friday, Rana and I measured the scatter coming from the 35W beam dumps.

(These are the ones with big aluminum heat sinks on the back that kind of look like little robots with 2 legs...inside the horn is a piece of polished silicon at Brewster's Angle.)

SETUP:

For the measurement, we used the Scatterometer setup at the 40m on the small optical table near MC2.

We used a frequency of 1743 Hz for the Chopper, and this was also used as the reference frequency for the SR830 Lock-In Amplifier.

The settings on the Lock-In were as follows:

Input A

24dB/octave

AC coupled

Floating input

"Low Noise"

Time Constant = 1sec

'Scope reading Output A, Output A set to 'Display', and A's display set to "R" (as in magnitude).

Sensitivity changed throughout the experiment, so that's quoted for each measurement.

MEASUREMENTS:

White Paper Calibration - white paper placed just in front of Beam Dump.  Sensitivity = 500microVolts.  Reading on 'scope = 7V

Laser Shuttered.  Sensitivity = 500microVolts. 'scope reading = 9mV.

Black Glass at Beam Dump location.  Sensitivity = 500microVolts.  Reading on 'scope = 142mV.   (DON'T touch the glass....measure the same setup with different sensitivity)

Black Glass at Beam Dump location (Not Touched since prev. measurement). Sensitivity = 10microVolts. Reading on 'scope = 6.8V

Laser Shuttered. Sensitivity = 10microVolts. 'scope Reading = 14mV +/- 10mV (lots of fluctuation).

Black Glass Wedge Dump at Beam Dump location. Sensitivity = 10microVolts. 'scope = 100mV.

Beam Dump with original shiny front plate. Sensitivity = 10microVolts.  'scope railing at 11V

Beam Dump with front plate removed. Sensitivity = 10microVolts. 'scope reading = 770mV

Beam Dump, no front plate, but horn's opening surrounded by 2 pieces of Black Glass (one per side ~1cm opening), BG is NOT flush with the opening...it's at an angle relative to where the front plate was.  Sensitivity = 10microV. 'scope = 160mV +/- 20mV.

Beam Dump, no front plate, only 1 piece of Black Glass. Sensitivity = 10microV. 'scope reading = 260mV.

Beam Dump, no front plate, 2 pieces of Black Glass, normal incidence (the BG is flush with where the front plate would have been). Sensitivity = 10microV. 'Scope reading = ~600mV

CALIBRATION:

Using our calibration numbers (Black Glass measured at 2 different sensitivities, not touching the setup between the measurements), we can find the calibration between our 2 different sets of measurements (at 500microV and 10microV), to compare our Beam Dump with regular white paper.

BG at 500uV was 142mV.  BG at 10uV was 6.8V.    6.8V/0.142V = 47.9

So the white paper, which was measured at 500uV sensitivity, would have been (7V * 47.9) = 335 V in 10uV sensitivity units.

This is compared to the BG wedge dump at 10uV sensitivity of 100mV, and the Beam Dump reading of 770mV, and the Beam Dump with-black-glass-at-the-opening reading of 160mV.

So our Silicon/Steel horn dump is ~8x worse than a Black Glass wedge and (335 / 0.77) = 435x better than white paper.

We used regular white paper as a calibration because it has a Lambertian reflectance. For some general idea of how to do these kinds of scatter measurements, you can look at this MZ doc.

Assuming that our white paper had a BRDF of (1/pi)/steradian, we can estimate some numbers for our setup:

Sensitivity (signal with the laser shuttered) = (0.02 / 335 / pi) = 2 x 10^-5 / sr.   This is ~3x worse than the best black glass surfaces.

Our wedge = (0.1 / 335 / pi) = 1 x 10^-4 / sr.  Needs a wipe.

Our Silicon-Steel Horn = (0.75 / 335 / pi) = 7 x 10^-4 / steradian.

Our measurements were all made at a small angle since we are interested in scatter back along the incoming beam. We were using a 1" lens to collect the scatter onto a PDA55. The distance from the beam to the center of the lens was ~2" and the detector's lens was ~20" from the front of the horn. So that's an incident angle of ~3 deg.

CONCLUSIONS:

* It seems that any front plate other than Black Glass is probably worse than just having no front plate at all.

* If we put in a front plate, it shouldn't be normal to the incident beam.  Black Glass at normal incidence was almost at the same level as having no front plate. So if we're going to bother with a front plate, it should be about 30deg or 40deg from where the original front plate was.

* No front plate on the Dump is about 7x a Black Glass wedge dump.

* The silicon looks like it might have some dust on it (as well as the rest of the inside of the horn).  We should clean everything.  (Maybe with deionized nitrogen?)

* We should remeasure the Beam Dump using polished steel at a small (30-40deg) angle as the front plate.

ATTACHMENTS:

* Photos taken with the Olympus camera, which has its IR blocker removed.

* In the photo you can see that we have a lot of reflection off of the horn on the side opposite from the silicon.

* The 2nd picture is of the scatterometer setup.

Attachment 1: P1090014_copy.JPG
Attachment 2: ScatterometerSetup.png
2507   Tue Jan 12 09:14:52 2010 steveSummaryGeneralScattering Measurements of 35W Beam Dumps

What was the power level, polarization and beam size at beam trap?

7402   Tue Sep 18 18:24:50 2012 JenneUpdateGeneralScattering in BS chamber or ITMX chamber

I have touched PZT2 such that the beam goes through the 45 degree non-iris target on the beam splitter.  This puts the beam at the center of ITMY, and without moving the BS, at the center of ITMX.  I say "at the center", but what I really mean is I put the target approximately at the center, within what looks like, say, 2 mm, by looking from above.  The target was many (5ish) centimeters away from the optic though, so that's why my side-to-side centering isn't so precise.  Given that, the beam was always more than half going through the hole of the target for both ITMs, so I'm claiming that the spots on the ITMs are within a few mm of center.

With this alignment, the beam was also hitting the center of the SRM (with all the same caveats).

I was able to get the SRM to retroreflect, while I still had Michelson fringing, so I think that I had the SRMI at least close to aligned (I was looking at the SRM retroreflection at the beam splitter, not all the way out to the AS port).  PRM is also pretty easy to align.

We're hitting the top of the AS camera, so I think things are pretty good.  I don't see beam on the REFL camera, but no investigation of that has been done as yet.

There is some scattering going on in the BS / ITMX chambers that's making me kind of unhappy.  I don't know how to get this to embed the youtube video, so here's the embed link, as well as the regular link:

youtube of AS and BS/PRM camera.

<iframe width="420" height="315" src="http://www.youtube.com/embed/QUbnMLXSS5U" frameborder="0" allowfullscreen></iframe>

Manasa watched the camera while I waved an IR card around in the BS chamber, and the only way I was able to get all the scatter spots to go away was to either block the beam incident on the BS (duh), or block the beam reflected off the BS, heading to ITMX.  Manasa said that the scatter spots still looked like they were fringing though, so I'm confused.  I may wave a card around in the ITMX chamber when I come back later tonight, to see what I can see.  Also, I just misaligned the SRM, and the scatter spots moved.  Now there's just some scatter off of what looks like the BS OSEM holders, as seen through the BS optic.

7948   Mon Jan 28 19:15:14 2013 ManasaUpdateScatteringScattering setup

[Jan, Manasa]

We are trying to get some scattering measurements in the Y-arm cavity. We have removed one of  the viewport windows window covers of ETMY chamber and have installed cameras on a ring that clamps to the window. The window along with the ring attachment is covered with aluminium foil when not in use.

7962   Wed Jan 30 11:18:31 2013 ManasaUpdateScatteringScattering setup

 Quote: [Jan, Manasa] We are trying to get some scattering measurements in the Y-arm cavity. We have removed one of  the viewport windows window covers of ETMY chamber and have installed cameras on a ring that clamps to the window. The window along with the ring attachment is covered with aluminium foil when not in use.

[Jan, Manasa]

To align the camera to see small angle scattering from the ITMY, we tried shooting a green laser pointer at the pickoff mirror that was installed in the ETMY chamber such that we hit the face of ITMY. But we concluded that to be a very bad way to align the camera because we have no means to reconfirm that the camera was exactly looking at the scattering from ITMY.

Since we are in air, we came up with a plan B. The plan is to temporarily install a mirror in the ITMY chamber to steer the beam from the laser pointer (installed on the POY table) through ITMY to the pickoff mirror at the ETMY end. This way, we can install the camera at the ETMY window and be sure we are looking at ITMY scattered light.

7971   Thu Jan 31 11:53:31 2013 ManasaUpdateScatteringScattering setup

 Since we are in air, we came up with a plan B. The plan is to temporarily install a mirror in the ITMY chamber to steer the beam from the laser pointer (installed on the POY table) through ITMY to the pickoff mirror at the ETMY end. This way, we can install the camera at the ETMY window and be sure we are looking at ITMY scattered light.

[Jan,Manasa]

We executed plan B. We installed the green laser pointer on POY table and steered the beam  through ITMY to hit the pick off mirror at the ETM end by installing *temporary mirrors. The pick off mirror was adjusted in pitch and yaw to center the reflected beam on the viewport window. We have installed irides on the ring attached to the viewport window to direct the beam to the camera.

*Temporary mirrors were removed from the ITMY chamber after this alignment.

8072   Tue Feb 12 23:22:14 2013 ManasaUpdateScatteringScattering setup

[Jan, Manasa]

We installed a camera at the ETMY end to look at the scattering pickoff from the ITMY. We were able to see the whole of the beam tube. We need to meditate on where to assemble the camera and use appropriate lenses to narrow the field of view such that we avoid looking at scattering from other sources inside the chamber.

5092   Tue Aug 2 11:52:44 2011 kiwamuSummaryGeneralSchedule

I have updated the 40m public calender.

Main change :

+ The vent starts from 3rd of August

+ Keiko and Anamaria (LSU) come from 13th of August

16648   Mon Feb 7 09:00:26 2022 PacoUpdateGeneralScheduled power outage recovery

[Paco]

Started recovering from scheduled (Feb 05) power outage. Basically, time-reversing through this list.

== Office area ==

• Power martian network switches, WiFi routers on the north-rack.
• Power windows (CAD) machine on.

== Main network stations ==

• Power on nodus, try ping (fail).
• Power on network switches, try ping (success), try ssh controls@nodus.ligo.caltech.edu (success).
• Power on chiara to serve names for other stations, try ssh chiara (success).
• Power on fb1, try ping (success), try ssh fb1 (success).
• Power on paola (xend laptop), viviana (yend laptop), optimus, megatron.

== Control workstations ==

• Power on zita (success)
• Power on donatella (success)
• Power on allegra (fail)  **
• Power on pianosa (success)
• Power on rossa (success)
• From nodus, started elog (success).

== PSL + Vertex instruments ==

• Turn on newport PD power supplies on PSL table.
• Turn on TC200 temp controller on (setpoint --> 36.9 C)
• Turn on two oscilloscopes in PSL table.
• Turn on PSL (current setpoint --> 2.1 A, other settings seem nominal)
• Turn on Thorlabs HV pzt supply.
• Turn on ITMX OpLev / laser instrument AC strip.

== YEND and XEND instruments ==

• Turn on XEND AUX pump on (current setpoint -->1.984 A)
• Turn on XEND AUX SHG oven on (setpoint --> 37.1 C) (see green beam)
• Turn on XEND AUX shutter controller on.
• Turn on DCPD supply, and OpLev supply AC strip on.
• Turn on YEND AUX pump on (fail) *
• With the controller on STDBY, I tried setting up the current but got HD FAULT (or according to the manual this is what the head reports when the diode temperature is too high...)
• Upon power cycling the controller, even the controller display stopped working... YAUX controller + head died? maybe just the diode? maybe just the controller?
• I borrowed a spare LW125 controller from the PSL table (Yehonathan pointed me to it) and swapped it in.
• Got YEND AUX to lase with this controller, so the old controller is busted but at least the laser head is fine.
• Even saw SHG light. We switched the laser head off to "STDBY" (so it remains warm) and took the faulty controller out of there.
• Turn on YEND AUX SHG oven on (setpoint -->35.7 C)
• Turn on YEND AUX shutter controller on.

== YARM Electronic racks ==

== XARM Electronic racks ==

* Top priority, this needs to be fixed.

** Non-priority, but to be debugged

16651   Mon Feb 7 16:53:02 2022 KojiUpdateGeneralScheduled power outage recovery

I went to the X end and found it was warm. Turned out that not all the A/Cs were on. They were turned on now.

Attachment 1: PXL_20220208_001646282.jpg
Attachment 2: PXL_20220208_001657871.jpg
16665   Fri Feb 11 11:17:00 2022 AnchalUpdateGeneralScheduled power outage recovery

I found that two computers are not powering up in the control room, Ottavia and Allegra. Allegra was important for us as it had the current version of LIGO CDS workstation installed on, providing us with options to use latest packages written by LIGO CDS team. I think the power issue should be resolvable if someone opens it and knows what thye are doing. Do we have any way of getting fuse repairs on such computers? Both these computers are Dell XPS 420.

16671   Mon Feb 14 21:03:25 2022 KojiUpdateGeneralScheduled power outage recovery

I opened the boxes. Allegra has obvious vent of at least 4 caps. And the power supply did not respond even a paper clip test was performed. https://www.silverstonetek.com/downloads/QA/PSU/PSU-Paper%20Clip-EN.pdf (Paper Clip Test)
=> The mother board and the PSU are dead.

Then Ottavia was also checked. The mother board looked OK, but the PSU did not respond. I quickly opened the PSU and it had a bunch of bulged capacitors in it. => PSU dead

Conclusion: Save the cards/memory etc as much as possible. Migrate the allegra HDD to any other healthy PC or obtain a new used PC from Larry. Otherwise, we just want to buy another WS and copy the disk in it.

Attachment 1: PXL_20220215_025325118.jpg
16669   Mon Feb 14 18:31:50 2022 PacoUpdateGeneralScheduled power outage recovery - IMC recovery progress

[Paco, Anchal, Tega]

We have been realigning the IMC as of last Friday (02/11). Today we made some significant progress (still at high input power), but the IMC autolocker is unable to engage a stable mode lock. We have made some changes to reach this point, including re-centering of the MC1 REFL beam on the ccd, centering of MC2 QPD trans (using flashes), and centering of the MC REFL RFPD beam. The IMC is flashing to peak transmission of > 50% its max (near 14,000 counts average on 2021), and all PDs seem to be working ok... We will keep the PSL shutter closed (especially with high input power) for now.

16672   Tue Feb 15 19:32:50 2022 KojiUpdateGeneralScheduled power outage recovery - IMC recovery progress

Reduced the IMC power to 100mW

Setup: The power meter was placed right before the final aperture (Attachment 1)

Before the adjustment: Initial position of the HWP was 37.29deg and the input power was 987mW (Attachments 2/3)

After the adjustment: Initial position of the HWP was 74.00deg and the input power was 100mW (Attachments 4/5)

The MC refl path optics has not been modified.

Attachment 1: PXL_20220216_001731377.jpg
Attachment 2: Screen_Shot_2022-02-15_at_16.18.16.png
Attachment 3: PXL_20220216_001727465.jpg
Attachment 4: Screen_Shot_2022-02-15_at_16.22.16.png
Attachment 5: PXL_20220216_002229572.jpg
16667   Fri Feb 11 16:09:11 2022 AnchalUpdateGeneralScheduled power outage recovery - Input power increased

We increased the input power to IMC by replacing the 98% transmission BS by a 10% transmission BS on the detection table (reverse of what mentioned in 40m/16408 see attachment 8-9). We then realigned the BS so that MC RFPD is centered. Then we realigned two steering mirrors to get the beam centered on the WFS1 and WFS2 QPD. Then we increased the power of the input beam to get 5.307 reading on the C1:IOO-MC_RFPD_DCMON channel. We did this so that we can align the IMC. Once we have it aligned, we'll go back to low poer for doing chamber work.

Beware, there is about 1W beam on the detection table right now.

16655   Wed Feb 9 16:43:35 2022 PacoUpdateGeneralScheduled power outage recovery - Locking mode cleaner(s)

[Paco, Anchal]

• We went in and measured the power after the power splitting HWP at the PSL table. Almost right before the PSL shutter (which was closed), when the PMC was locked we saw ~ 598 mW (!!)
• Checking back on ESP300, it seems the channel was not enabled even though the right angle was punched in, so it got enabled.
• No change.
• The power adjustment MEDM screen is not really working...
• Going back to the controller, press HOME on the Axis 1 (our HWP) and see it go to zero...
• Now the power measured is ~ 78 mW.
• Not sure why the MEDM screen didn't really work (this needs to be fixed later)

We proceeded to align the MC optics because all offsets in MC_ALIGN screen were zeroed. After opening the PSL shutter, we used values from last year as a reference, and try to steadily recover the alignment. The IMC lock remains at large.

16657   Thu Feb 10 15:41:00 2022 AnchalUpdateGeneralScheduled power outage recovery - Locking mode cleaner(s)

I found out that the ESP300 service needs to be run in root mode for it to be able to connect to the USB port of HWP motor controller. While doing this change, I noticed that the channels hosted by c1psl might have a duplication conflict with some other channel hosting computer, because a lot of them show the Warning: "Identical process variable names on multiple servers" which is not good. Someone should look into this conflict.

I added instructions on the power control MEDM screen as it was very non-trivial to use. I have set the power such that the C1:IOO-MC_RFPD_DCMON is 5.6 and this happened at C1:IOO-HWP_POS_SET 2.29.

16658   Thu Feb 10 17:57:48 2022 AnchalUpdateGeneralScheduled power outage recovery - Locking mode cleaner(s)

Something is wrong with the Video MUX. The system did not turn back on with full functionality. Even though we see the screens as they were before the power shutdown, we have lost control on switching any of the videos. I went to check the wiki page about Video MUX which told be we should be able to see the configuration screen on this link, but the page wasn't opening. I went and removed the power cable and put it back in. That brought back the configuration page. Still, I could not change any of the video feeds however this time, I could see the EPICS channel values (like C1:VID-QUAD1_4) change. I tired to go to the configuration page and change the matrix values from the control tab there. I found out that the matrix was mislabeled and while making the changes, I started seeing blue screen on QUAD1_3 (where MC2T was set before). I set the QUAD1_3 (output 23) to MC2T (input 16), but no change. The EPICS values are also set properly, so I don't understand the reason behind blue screen. The same happened when I tried to use:

Weirdly, this caused the QUAD1_4 screen to go blue. Running following had no effect:

So, I'm not sure what to do. This really needs to be fixed! I wanted to see teh MC2F camera so that I can align IMC, that was the whole reason for this rabit hole. Help needed.

Attachment 1: PXL_20220211_021509819.jpg
16659   Thu Feb 10 19:03:23 2022 KojiUpdateGeneralScheduled power outage recovery - Locking mode cleaner(s)

I came back to the 40m and started the investigation.

If I ping 192.168.113.92, it responds. But telnet (port 23) was rejected. I somehow tried ssh and it responds! I even could login to the host using usual password. Here is the prompt.

controls@nodus|~> ssh 192.168.113.92 controls@192.168.113.92's password:
...
controls@c1sus2:~ 0$ Oh no... Looks like c1sus2 and the videomux have the IP address conflict. Here are the useful ELOG links: https://nodus.ligo.caltech.edu:8081/40m/4498 https://nodus.ligo.caltech.edu:8081/40m/4529 16660 Thu Feb 10 19:46:37 2022 KojiUpdateGeneralScheduled power outage recovery - Locking mode cleaner(s) == Assign new IP address to c1sus2 == - Shutdown c1sus2 (Oh, no. This killed c1lsc/c1sus/c1ioo... This should be taken care of later) - Confirmed 192.168.113.87 is not alive - Go to chiara - Modify /diskless/root/etc/hosts 192.168.113.87 c1sus2 c1sus2.martian  - Modify /etc/dhcp/dhcpd.conf host c1sus2 { hardware ethernet 00:25:90:06:69:C2; fixed-address 192.168.113.87; }  - Modify /var/lib/bind/martian.hosts c1sus2 A 192.168.113.87 videomux A 192.168.113.92  - Modify /var/lib/bind/martian.hosts/rev.113.168.192.in-addr.arpa 87 PTR c1sus2.martian 92 PTR videomux.martian  - Reload/restart bind9 / dhcpd. Run the following command sudo service bind9 reload sudo service isc-dhcp-server restart  - Restart c1sus2 and confirm if the IP address was actually changed controls@c1sus2:~ 0$ /sbin/ifconfig
...


== Restart c1lsc / c1sus /c1ioo ==

- Reboot c1lsc/c1sus/c1ioo

- Go to scripts/cds

- Run startC1LSC.sh and follow the instruction

15956   Wed Mar 24 00:51:19 2021 gautamUpdateLSCSchnupp asymmetry

I used the Valera technique to measure the Schnupp asymmetry to be $\approx 3.5 \, \mathrm{cm}$, see Attachment #1. The data points are points, and the zero crossing is estimated using a linear fit. I repeated the measurement 3 times for each arm to see if I get consistent results - seems like I do. Subtle effects like possible differential detuning of each arm cavity (since the measurement is done one arm at a time) are not included in the error analysis, but I think it's not controversial to say that our Schnupp asymmetry has not changed by a huge amount from past measurements. Jamie set a pretty high bar with his plot which I've tried to live up to.

Attachment 1: Lsch.pdf
ELOG V3.1.3-