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AdV-DAQ (Calibration)
melo, rolland, grimaud - 14:17 Tuesday 14 January 2025 (65974) Print this report
NE PCal alignment check (to investigate 0.8% power mis-calibration) + NE,WE Pcal sensing noise measurements

NE PCal on-site check to investigate the 0.8% mis-calibration of NE PCal power

This morning, from 9h to 9h45 UTC, we have worked on the NE PCal to investigate a possible explanation for the 0.8% power mis-calibration of the NE PCal (which I recall was renormalized on the NE NCal before the start of O4b to fix this issue).

Suzanne went at NE and had a look at the beam alignment, first on the injection Tx bench (from around 9h10), and then on the reflection Rx bench (around 9h20 UTC).

The tested hypothesis for the 0.8% mis-calibration was optical losses between the NE mirror and the NE Rx sphere, possibly due to beam misalignement on the Rx bench. On the bench, there are three optical elements: diaphragm just after the viewport, a steering 1 inch mirror and the integrating sphere with 1 inch aperture.

After visual inspection, the alignment looks fine on all optics.

In order to test if the diaphgram aperture was too small, Suzanne has increased it by a large amount but it had no impact on the power reaching the Rx sphere. The diaphragm aperture was put back to a similar value as before.

Suzanne did not notice any big dust on the viewport, but this is difficult to inspect with the surrounding elements, and with no green light.

Benches closed and power loop closed again around 9h35 UTC.

Around 9h40-45, we tried to reconnect the Hameg28 power supply for slow monitoring, but without success.

--> the NE PCal 0.8% mis-calibration is not coming from bad beam alignment on the Rx bench nor from too small diaphragm aperture.

________________

Measurements to study sensing noise of photodiodes and spheres

For each time, the duration is more than 60 s, more around 120 s. Times given in UTC.

  • 10h05 : NE laser off (pump not disabled)
  • 10h08m30s : NE and WE laser at 0.3 W, w/o loop
  • 10h11m15s : NE and WE laser at 0.3 W, w/ loop
  • 10h13m45s : NE and WE laser at 0.6 W, w/o loop
  • 10h15m15s : NE and WE laser at 0.6 W, w/ loop
  • 10h18m40s : NE and WE laser at 1.0 W, w/o loop
  • 10h23m25s : NE and WE laser at 1.0 W, w/ loop
  • 10h26m00s : NE and WE laser at 1.3 W, w/o loop
  • 10h29m20s : NE and WE laser at 1.3 W, w/ loop
  • 10h36m20s : NE and WE laser at 2.0 W, w/o loop
  • 10h38m30s : NE and WE laser at 2.0 W, w/ loop
  • 10h42m45s : NE and WE laser off (pump diode not off),
  • 10h45mxxs : requested 2.6 W, maximum reached ~2.2 W
  • 10h46m20s : NE and WE laser at 2.2 W, w/o loop
  • 10h47m30s : NE and WE laser at 2.2 W, w/ loop

Back in nominal conditions (1.3 W, w/ loop, and permanent lines on) at 10h53m UTC.

The plots below show the noise spectrum of the sensors during these different measurements, first w/o loop and increasing laser power, the w/ loop and increasing laser power. The last plot show the noise spectrum with laser off.

 

Images attached to this report
Comments to this report:
grimaud - 17:49 Thursday 16 January 2025 (65992) Print this report

Following the measurement made during the maintenance, here are plots of the evolution of the power from 0.3W to 2.2 W for each PCal sensors.
The first 3 plots are without the control loop and the next 3 plots are With the control loop.

Images attached to this comment
grimaud, rolland - 15:37 Tuesday 21 January 2025 (66020) Print this report

Looking at the measurement made during the last maitenance we realised that when the PCal permanent lines were on, the noise level of the photodiodes was increasing compare to when the lines were off (see plot 1 were the reference plot is without permanent lines compare to with permanent lines with standard amplitude)
We did some more test to see were this is coming from on WE during maintenance today.

1/ Testing line injection with CALNoise
2/ Testing lines injection with PCal_Fast

1/ Testing line injection with CALNoise

First we acted on WE PCal lines using CALNoise, we switched the lines off and then tried to switch back on one line at a time to see which one were causing the noise to rise.
WE PCal has 3 permanent lines at the following frequencies and amplitude :
- 36.28 at 1.5e-3
- 38.5 at 2.0e-3
- 994.5 at 200.0e-3

The amplitudes were choosen in order to get the same SNR on all injected lines.

When putting one line at a time it appeared that the issue was coming from the 994.5 Hz line only (see plot 2 with reference plot without lines compare to when we inject only the 994Hz line).
We wanted to see the threshold in amplitude were the noise starts to increase. To test this we changed the amplitude of the 994.5Hz line starting at 2.0e-3 up to 37e-3 were we started to see the noise increase.
See plot 3 where we compare the noise without injection to the one where the 994Hz line is injected at 37e-3 amplitude.
Something intersting to note is that the noise level of Tx_PD1 and Tx_PD2 is higher for the 37e-3 amplitude than it was when injecting at 200e-3 and also when injecting all the lines at normal amplitude. It is not clear why.

We did the same test for the 38.5 Hz line to see if we would see the same effect by increasing the amplitude and the same thing append around ~30e-3.
See plot 4 comparing without lines to injecting the 38.5 Hz line at 37e-3.

Timestamps (For 60 s each time)

  • Cutting line off --> 8h15'15''
  • 38.5Hz (2.0e-3) --> 8h22'30''
  • 36.7Hz (1.5e-3) and 38.5Hz (2.0e-3) -->8h25'30''
     
  • 994.5Hz (200e-3) --> 8h28'00''
  • 994.5Hz (2.0e-3) --> 8h32'30''
  • 994.5Hz (20e-3) --> 8h34'45''
  • 994.5Hz (40e-3) --> 8h38'00''
  • 994.5Hz (30e-3) --> 8h40'00''
  • 994.5Hz (35e-3) --> 8h41'40''
  • 994.5Hz (36e-3) --> 8h43'00''
  • 994.5Hz (37e-3) --> 8h44'40''
     
  • 38.5Hz (37e-3) --> 8h46'15''
  • 38.5Hz (10e-3) --> 8h47'45''
  • 38.5Hz (20e-3) --> 8h50'15''
  • 38.5Hz (30e-3) --> 8h53'00''
  • 38.5Hz (31e-3) --> 8h55'45''

2/ Testing lines injection with PCal_Fast

One of the hypothesis on this is that it could be caused by communication issue with CALNoise. To test this we tried injecting the same lines but using the PCal _fast process directly.
Fisrt we tried to inject the 38.5Hz line at 2.0e-3 amplitude to check that it was working but accidentelly injected a noise at 10e-3. After this we were able to do the other injections but we noticed that the noise level of Tx_PD1, in particular, was higher without the calibration lines than it was before (see plot 5 where we compare the noise without noise injection that was acquired at 8h15'15'' at the beginning of this test, to the noise acquired at 9h32').

Then we tried to see if we could reproduce the same noise increase seen in the previous test with CalNoise. First we tried with the 38.5Hz line and found that the amplitude needed to get the noise increase was more around 50e-3 rather than the 37e-3 seen in the previous test (see plot 6 for the injection of 38.5Hz line at 50e-3). We did the same thing with the 994.5Hz line and found that the noise increase was seen around an amplitude of 30e-3  (see plot 7).

We also did another inejction at low frequency at 4.5Hz at 30e-3 of amplitude to see how it affected the noise level. In plot 8 we can see that it increase the noise in the same way than with the 38.5 and 994.5Hz lines.

To conclude it does not appear that this increase in noise is coming from using CAlNoise as using directly PCal_fast is not improving the noise level.

Timestamps (For 60 s each time)

  • accidentely injected a 1e-3 noise  --> 9h08'13''
  • Cutting lines off --> 9h09'15''
  • 38.5Hz (2.0e-3) --> 9h31'00''
  • Cutting lines off --> 9h32'00''
     
  • 38.5Hz (2.0e-3) --> 9h33'40''
  • 38.5Hz (37e-3) --> 9h34'50''
  • 38.5Hz (50e-3) --> 9h36'05''
  • Cutting lines off --> 9h37'20''
     
  • 994.5H z (200e-3) --> 9h38'30''
  • 994.5H z (30e-3) --> 9h40'15''
  • 994.5H z (20e-3) --> 9h41'30''
  • 994.5H z (30e-3) --> 9h43'10''
  • cutting lines off --> 9h44'20''
     
  • 4.5Hz (30e-3) --> 9h45'00''
  • 4.5Hz (20e-3) --> 9h46'10''
     
  • Cutting lines off --> 9h48'00''
  • Putting normal lines back on --> 9h48'50''
Images attached to this comment
masserot - 12:01 Wednesday 22 January 2025 (66036) Print this report

Today  only the numerical noise computation is performed, none mitigation of this noise is done .

The plot compares the channels related to the photodiodes, the ones related to the filter computation and the filtering numerical noise with (purple) and without(blue)  PCAL lines .

From this plot, the numerical noise (DigitalNoise_corr) remains at the same level with or without the PCAL lines, meaning that the observed extra noise is not due to the filters computation

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