The goal was to see if there are differencies when the transformer is plugged into the experimental UPS mains or into the IPS "ENEL" mains.
In the attached plots (one in LOG scale, the other in LIN scale) it's clear visible that the measured stray magnetic field is much higher when the transformer is powered with the experimental UPS line.
This is in agreement with recent measurements done with the so called "mains sniffers" (they are just small transformers, whose low-voltage output is connected to an ADC): the UPS line is always noiser than the IPS line.
We don't know if the culprit is the UPS machine itself or if this noise is due to the loads powered with this line. The only "ultimate" test should be to switch OFF the UPS, leaving VIRGO running under normal IPS line for some minutes. If this is too dangerous (mains drop-out, etc.) we can run under DIESEL generator.
