Takahashi, Lucia

In order to understand if the origin  of the observed lines are  aliases of higher frequency or not, last Wednesday, we measured the spectra of the LVDTs with the analogue spectrum analyzer. We observed that even in this configuration the noise did not disappear and  we concluded that the problem was not connected with to the  digital system, but perhaps it was connected to the frequency of the demodulation signal (standard 10Khz).
To verify this, we changed the demodulation frequency from 10 Khz to 10.3 Khz. We observed that, by using this new demodulation frequency, the LVDT signals show less noise  and that the 70 Hz line is reduced a lot. We attached here the plot where the comparison of the LVDTs spectra, by using both demodulation signals   (red curve= 10 Khz demodulation, blue curve= 10.3  Khz demodulation,)  are shown.