This morning, alain realized that the SWEB local controls shows much higher noise than usual, this can be seen in the vim plot, see figure 1 where we see that the noise in the controls of the angular d.o.f. increased a lot between 22:00 and 23:00 UTC.
Figure 2 shows that it happens roughly wednesday 25th of January at 22:37 UTC.
Figure 3 shows the spectra of the angular d.o.f. and their correction before and after the increase of noise.
We looked at the raw read-out signals of SWEB before and after the increase of noise, see figure 4, we see that the noise around 10 kHz was already high but it increased even more resulting in a reduction of the SNR for the demodulation of the lines around 10 KHz that probably causes the increased of noise.
We don't have clear explanation for that behaviour or what could have caused the noise increase last wednesday, one could think that it could come from the "Nikhef box" used to read-out the LVDT signals.
We then checked all other benches :
- SDB1, figure 5, all signals looks OK.
- SQB1, figure 6, all signals looks OK.
- SDB2, figure 7, all signals have a very high noise above 200 Hz and even the noise floor is higher than on other bench. To be noted that the noise in the local controls is similarly low to other bench.
- SIB2, figure 8, all signals looks OK.
- SNEB, figure 9, all signals looks OK.
- SPRB, figure 10, all signals looks OK except FL_V that shows higher noise between 1-6 KHz.
- SQB2, figure 11, all signals looks OK except BR_V that shows higher noise between 0.5 and 8 KHz.