As shown in a previous entry, a strange event detected by the channel Sc_WE_MIR_Z (and the others generated by MIR_PSDI) is coincident with a loss of dark fringe alignment, mainly due to a rotation of WE in TY. As we can see in fig 1, the coincidence is not perfect: the aligment problem occurs a few secons erlier than the noise.

In fig 2 we can see that the channels generated by PSDI are not the only affected by the noise: Sc_WE_tyAA is a channel generated in the same board (ScWEPSDi), sent to the master board and then to the DAQ. It makes the same path of the channels form PSDI, but has no correlation with that device.

In fig 3 we have a zoom of a noisy event: both signals goes quickly towards zero. Considering that DSPs run at 40kHz and DAQ shows the signals at 10 kHz, this is compatible with the loss of one sample at 40 kHz.

Observing the same event when the ITF is not locked and MIR_Z is used in loop to damp the mirror, we can notice that the noise dose not enter the loop correction (fig 4, fig 5). This means that the same channel, sent to a different board (MIR coil driver), is not noisy. It looks like a problem of communication between PSDi board and master board.

Anyway, the problem is no more there since a couple of days: the debugging is a bit difficult.