[Kiwamu, Lisa, Keita, Matt, Giacomo]

At about UTC 2013-01-22 21:17:40, the IMC_REFL_DC channel suddenly showed and offset of about -8000 counts. In the past week it has been consistently reading between about 50 (IMC locked) and 450 counts (IMC unlocked). The attached plot IMC_REFL_DC_trend shows the trend in the last 12 days, witht he "jump" visible at the extreme right.

The signal still changes by about 400 counts between the IMC locked and unlocked statuses, and the RF part seems to be fine as the IMC locks regularly.

By inserting a breakout board at the input of the interface, we did verify that the power supply readings (+-18 V) were normal and that the offset came in fact from a bias of about 2.2 V on the REFL_DC readout. It does thus appear to be a problem with the head, or anyhow with something downstream of the interface.

It is curious to note how all the WFS channels show something going on at the exact same moment that the offset appeared (see attached plot IMC_REFL_DC_zoom). It is not clear if the problems seen on the WFS (see entry 5207) are related to this, if working on WFS debuging triggered the problem on the REFL_DC or if the two things are completely unrelated.