This morning, the offsets of the SDB1 B5 quadrants were checked and updated.

From Fig.1 one can observe:

• before 06h39 utc the IMC is stil locked and one can observe some signal on the SDB1 B5 quadrants (B5_QD1_sum fluctuates around 11-12, and B5_QD2_sum fluctuates  around 13).
• at about 06h39 utc the IMC is unlocked, and one can observe residual offsets on the quadrant channels.
• at 06h42m46 utc the old offset corrections are removed from the SDB1_Quadrants config file and one can measure the total offsets by reading the B5 quadrants channels (see zoomed plots on Fig.2 for a better view).
• at 06h53m38 utc, the configuration of the process SDB_EDB_dbox_rack is reloaded after correcting these offset values. All channels of the quadrants are then equal to 0 (as expected from the offset subtraction), including the sum channels.
• at about 07h11 utc, the IMC is locked again. One can see that the offsets on B5_QD2 had an almost negligible impact on the sum channel. However the DR, UR, UL channels have changed by about a factor 2, compared to the situation before offset correction.

It was then possible to reengage the bench drift control without problem.