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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 Channel

    We 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