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Environmental Monitoring (Environmental Monitoring)

L. Mobilia, A. Longo - 18:02 Friday 31 March 2023 (59564)

Heater and Compressor Noise in NEB

During the analysis of the seismic noise associated to the heater cycle (INF_NEB_HEATER_TE) in ENV_NEB_SEIS_N we found that

The noise in the seismograph disappears when the heater have been changed (from 27 jan 2023 to 05 Feb 2023).
A new noise appears in the velocimeters sensors array (NN_NEB_ACC_07,08,09) arond ~35 Hz and ~145 Hz. See HEATER_ACC_Z_0809_050218001830.png and NEB_ACC_08_08_1hour_5022023.png

These noises where related to:

the ~145 Hz associated to the NEB_COMP1_PRES. See glitch145Hz_COMP1_PRES.png
the ~35 Hz associated to the INF_NEB_AIR_PRES (now called INF_NEB_AIUR_COMP_LINE_PRES). See glitchNN_zoom.png

The first one (COMP1) is the compressor, the latter one (AIR_PRES) is a channel which follows the compressors 1 and 2.

For further inforation see LogBook_Draft4.pdf

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LogBook_Draft4.pdf

Comments to this report:

fiori, dattilo, soldani, mobilia - 0:08 Saturday 01 April 2023 (59576)

We inspected the NEB air compressors room and identified the device responsible of this noise. It is the air dryer of the compressed air circuit. Figure 1 shows a picture of the device. Figure 2 shows the location of probe ENV_NEB_ AIR_COMP_LINE_PRES. Every 2 minutes or so this device produces an air puff in order to expell condensed water. This puff is associated to an audible acoustic noise. Red circles in Figure 3 indicate the measured times when the dryer puffed during our visit. These times match well with maxima of ENV_NEB_AIR_COMP_LINE_PRESS and noise transients in the NN_ACC sensor (inside NEB hall) and the NN_INF_07 microphone which is located in the water pumps room next to the compressors room.

The puffs of the dryer produce a little drop (~0.2 bar) of the pressure in the compressed air circuit, which seems to trigger (every even time) the start of the compressor.

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