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AdV-INF (Environmental noise mitigation)
Paoletti, Fiori, Tringali, Soldani - 16:36 Wednesday 27 October 2021 (53672) Print this report
Increase of Magnetic noise in CEB (and possible correlation with Humidity controls)

A couple of weeks ago (10 october) we had an anomalous increase of the magnetic field in CEB. It was a broad noise, started slowly and then increased to high levels.

The same was visible in the IPS voltage and current monitors, in all three phases

The noise stopped abruptly on the morning of October 12th, at 06:45 UTC (8:45 LT), when an external company began servicing the Detection HVAC machine.

Speaking with Davide, we understood that every now and then (a month in winter, more rarely in summer) a humidifier needs to be changed because its internal tank fills with limestone. This type of humidifier (service manual is attached to this entry as PDF file) uses the three-phase mains line (400Vac, 7.5kVA) for the production of water vapor. It is thought that the amount of power is controlled (maybe a PWM system?), and it is said by Davide that when the amount of residual limestone is at its maximum, it becomes such as to create sparks. This is why it needs to be changed from time to time with a new one.

Looking at the HVAC data, we can see a vague correlation between the humidity of the outdoor ambient air (METEO_HU) which is low, the HVAC controls that are (or are running) high and the noise increasing (end of life of the humidifier).

To support this theory we need to install some current sensors on both HVAC machines and wait for the next similar noise increase.

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fiori, tringali, soldani, dattilo, lunghini - 18:50 Thursday 23 October 2025 (68023) Print this report

VIM spectrograms showed and increased rate of broadband magnetic glitches inside the CEB hall, which occurred since last week: Figure 1. Also seen by the IPS VOLT probe: Figure 2. 

The signature reminded us of the noise from the DET HVAC humidifier encoutered 4 years ago (!): https://logbook.virgo-gw.eu/virgo/?r=53672.

As reported in Figure 1, the glitches disappeared when one of the two humidifiers (electrolitic type) got stuck on Sun. Oct 19. On Tuesday morning this humidifier helectrodes were cleaned (with time electrodes get covered by limestone and surge larger currents). The glitches rate reduced but did not disappear.

In recent times Roberto Cavalieri implemented current monitors of both humidifiers (named INF_CEB_HUM_1 (main) and INF_CEB_HUM_2 (spare)). These sensors help to charaterize the humidifiers noise.

Thanks to the monitors,  we can tell that some glitches from the humidifiers (at least one every few minutes) are always present, and seen both in magnetometers and Voltage / Current IPS monitors of CEB (Figure 3). Also, according to the monitors, since Tuesday intervention both DET humidifiers are active (Figures 4 - September, Figure 5 - October, Figure 6 - October full).

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