After verifying the BPC signals calibration (entry #51205), we have analyzed them from January 2021 to the end of March 2021 in order to see if the signals present any drift trends. For that purpose, we have applied an unwrap technique to all signals (X, Y, TX and TY), i.e., we have considered all the moments in which we have brought the BPC to the center of the corrections, and summed the signals in order to see the long term effect.
The results have been the following:
For TX and TY there has been a positive and negative drift respectively of the order to two hundred micro-radians.
For X and Y, instead, there has been a negative and positive drift, respectively, of the order of a few mm (3 mm for X and 5 mm for Y).
We are still investigating to understand better what could be the cause of this effect.