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By applying the same procedure to the set of 20 29 runs from the period June 28 - July 22 30 (~1 run per day), one can obtain the evolution of pedestal temperature vs day from June 28 (top plot):
On the bottom plot the real CAL temperature (average of all AFEE board temperature for the whole run) was subtracted from "pedestal temperature", showing the effect of pedestal drift NOT related to temperature variation.
This drift is negative and has initially had the rate equivalent to the temperature drift ~1 deg ped week. After 3 weeks the slope is clearly decreasing and the behaviour now is close to exponential approaching some stable value - according to the fit with function y = p0*(exp(-t/p1)-1), the parameters are: p0 = 6.2 deg (stable pedestal temperature), p1 = 28 days (time constant). This is a good news - if the drift will stop, it will greatly simplify the CAL calibration. But it is not excluded that drift will just arrive to different constant rate.
I'll continue to monitor this non-thermal pedestal drift.