The error signal of the BPC TY was around +40 urad and reached +60 urad when the interferometer is in carm_null and the BPC uses the arms cavities as reference. This is due to the work of yesterday 69820, the laser beam was moved w.r.t. the ITMs.

With 60 urad we reached the limit of the linearity zone of the quadrant and were limiting the possibility to keep on shifting the beam towards the ITF. Today from 16:20 to 16:40 utc, we slightly tilted horizontally the EIB_BPC_M5 mirror in front of the FF QPD. Now the TY signal is at -20 urad. We changed the TY setpoint to -20 urad in the BPC DSP board.

The injection system relocked properly after the intervention.

To be noted the FF QPD of the BPC can not be taken as an absolute reference of the beam we sent towards the ITF. Or better, the absolute reference has been moved by -60 urad in TY.