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User name D. Parno
Log entry time 17:32:57 on August 25, 2009
Entry number 285943
keyword=Compton: FADC pedestal value for GSO ChannelWe took a photon detector run with HV off to make a precise measurement of the pedestal for the FADC channel measuring the signal from the GSO crystal (CMU DAQ).
Figure 1 shows the raw signal from Accumulator 0 (no thresholds). Since the HV is off, this is pure FADC noise. It is plotted with the results of a Gaussian fit.
Taking the mean value of the Gaussian and dividing by the 6,600,998 samples taken in each MPS gives us a measured pedestal value of 3700.667.
Figure 2 shows the pedestal-subtracted signal from Accumulator 0, using
this new pedestal value. If everything worked well, this should be
centered on zero. As you can see, everything did work well: the mean is
consistent with zero. A mean value of 90 represents an error of one ten
thousandth of an FADC channel in the pedestal.
A copy of this log entry has been emailed to: gbfranklin@cmu.edu, mfriend@andrew.cmu.edu
Figure 1
Figure 2
