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Environmental Monitoring (Environmental Monitoring)
janssens, Fiori, Paoletti - 13:41 Tuesday 21 January 2020 (48205) Print this report
Investigation magnetic noise EER
The last days we noticed some magnetic noise in the external as well as central building magnetometers. The noise is situated around 86Hz and it appears and disappears, it is also visible at the mirror value around 50Hz. The noise is also seen in the IPS voltage of CEB and at the "electric" probe in the CEB. (Fig 1-3)
It is unclear if the irregular noise observed in the external magnetometer is linked to the lines at 86Hz which appears and disappears.

After further investigation we linked it to the cooling pattern in the EER room. (Fig4)

Today around 8:30 UTC we installed two portable magnetometers in the EER room. On on top of the splitter system, the other on top of the most active fan coil. (Fig 5-7)
Somewhere between 8:30-9:30 UTC we played very briefly with the fan coils by turning them off and on. The order in which they were switch is:
right fan coil OFF
left fan coil OFF
right fan coil ON
left van coil ON

Afterwards we noticed that the noise was not seen in the CEB and EXT magnetometer since Sunday (19/01) around 16:00 UTC.
This seemed to be correlated by a change in cooling pattern in the EER room. the 'critical-temperature' of 22°C was not reached anymore.

We mention that the fan coils are always active and there temperature output only changes as the water-flow through them changes.
The splitter on the other hand is set on a temperature of 22°C and turns of when needed. The external part of the splitter is located outside CEB between the MC tunnel and the WE tunnel.

Afterwards we decided to do an additional test. Around 10:15 UTC both fan coils were turned off and the splitters working temperature was decreased to 16°C (it's minimum).
All systems were reset to there normal working conditions around 11:15 UTC. (Fig 8) Some time period afterwards still shows some non-normal conditions in magnetic noise.

The noise at 86Hz did not appear when the splitter was forced to work. (Fig 9-10) However it seems there is some noise - which might or might not resemble the irregular noise sometimes seen together with the regular noise (Fig 1) - in the external magnetometer while the splitter is forced to work. This is not visible inside.

At this moment we cannot make any conclusions and further investigations are needed. Further investigations will most likely include placing a magnetometer near the outside part of the splitter.
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Comments to this report:
janssens - 15:53 Wednesday 22 January 2020 (48217) Print this report

Similar noise also appeared in April 2017, see logbook entry 37121
Also then evidence was pointing towards the splitter cooling machine in the EER room.
This splitter was installed earlier that year (Jan 2017)

janssens - 16:03 Wednesday 22 January 2020 (48219) Print this report

Follow-up investigation:

At roughly 16:00 UTC in 21/01 the similar temperature regime as before was reached. (Fig 1) However this was not always the typical temperature behaviour of the room, but only from rhougly 30/12/2019.

At this point we see the 86Hz line after the switch on and off in ENV_EER_MAG_1 (on top of the splitter), not in ENV_EER_MAG_2. The signal in ENV_EER_MAG_1  matches nicely with the temperature changes and the observed signal in ENV_CEB_MAG_N. (Fig 2-3) However the latter is in a noisier environment and is (almost) blind to the signal.
We already knew there was a mirror image at 14 Hz. In the earlier (2017) report of the similar noise it was mentioned it went all the way up to 400 Hz. It was controlled and it wee see it indeed at 114Hz and 186Hz as well. Higher frequencies were not checked.

Why we did not see anything when we forced the switch on of the splitter yesterday is unclear.

The magnetic noise in ENV_EER_MAG_1 is roughly two orders of magnitude larger than in ENV_CEB_MAG_N, which is on its turn one order of magnitude larger than in ENV_EXT_MAG_N.

As a final remark: we see nicely that at the start of the signal it increase rapdily to 86 Hz (or decreases to 14Hz) over a distance of about 18-19Hz. (Fig 4)

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janssens, paoletti - 11:18 Thursday 23 January 2020 (48230) Print this report

Today we moved the probe ENV_EER_MAG_2 between 9:10 and 9:25 UTC times.

It is no longer on the fan coolers, but on the external part of the splitter of the EER room.

See pictures for the current set-up. The location is between the MCB-tunnel and the west arm tunnel.

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janssens - 13:49 Thursday 23 January 2020 (48233) Print this report

Source located

Only 40 minutes after moving ENV_EER_MAG_2, the splitter turned on and we were able to see a clear signal in both ENV_EER_MAG_1 and ENV_EER_MAG_2. In the latter the signal is larger by roughly two orders of magnitude. (See figure)

We determine the source to be the outside part of the splitter.

Furthermore we notice that here we see the noise all the way upto 5 kHz, which is the full available data which is being read-out by the data-acquisition.

 

Now further investigation is needed to determine:

- The path of coupling: how the magnetic noise from the external part of the splitter couples to both the CEB and EXT magnetometers.

- The reason of the noise: why this specific machine produces the noise. Do others produce similar noise or not?

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janssens - 11:00 Friday 24 January 2020 (48239) Print this report

ENV_EER_MAG_2 is now moved from on top of the splitter of the EER room to on top of the external part of the splitter of the Injection electronic room. 7.52 UTC. This is directly below the splitter of the EER room.

Goal: make comparence between the two machines.

Important note: we noticed the probe was moved during its observation. Initially it was on the rigth-end of the machine this morning it was at the left end. This means the data might show differences due to change in location.

Therefor we taped the probe onto its current position. 7.59-8.07 UTC

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Paoletti - 15:14 Friday 24 January 2020 (48243) Print this report

Due to the bad weather forecast, I have removed the external magnetic probe at 13:20 - 13:25 UTC, leaving it just after the door, below the MC pipe.

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janssens, fiori, paoletti - 11:53 Tuesday 28 January 2020 (48267) Print this report

ENV_EER_MAG_2 was moved on Monday 27/01 between 16.02 UTC and 16.09 UTC. I moved it from below the MC tube to on top of the MC tube to be closer to the tube and have a look at possible magnetic noise carried by the tube from the MSB to the CEB. Also added a figure containing the RMS of the probe and one of the current chanels of the MCB. There is clearly so comherence. Further investigation will follow.

ENV_EER_MAG_1 was removed on Tuesday 28/01 at 09.07 UTC. This descision was made since we have sufficient evidence of the splitter in the EER room and the outside part being the source of the noise being investigated. The channel has been deactivated from colleting data.

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