[Halld-tagger] Microscope beam test

[Alexander Somov]

Hi,

I've started checking  quality of the microscope beam 
test data.

Richard, I don't see any saturation of the FADC signals
of the single-channel SiPMs, the problems which you have 
mentioned during the last beamline meeting (at least for 
the runs I've checked). Please send me the run numbers. 
You can find some plots in the directory
www.jlab.org/~somov/micro

As an example, files run147_sum_fadc.jpg and run147_single_fadc.jpg
contain FADC distributions of the 3 sums and 5 separate SiPM channels,
respectively:
- left plots:  maximum adc amplitudes in 500 ns time window ( 125 samples),
               i.e., max amplitude is determined in every event in this
               time window and is stored in the histo.
- right plots: average fadc sigmal amplitudes in 500 ns time window.
                Time coincidence between the trigger and the
                corresponding SiPM channel was required.

Note:
-----
    An amplitude in the 10-bit FADC is coded in the same way
    as in the 12-bit FADC, with 13 bits. The most significant bit
    stands for the overflow bit. 12 bits are used for the amplitude
    itself. For the 10-bit FADC, two less significant bits are
    just not used; if you read out 12 bits, the amplitude can be
    larger than 1024.

    For 5 individual SiPM channels we used the FADC range 0 - 500 mV.
    The range for the 3 sums was set to 1 V.



Brief summary:
- FADC spectra for the single channels 2 & 3 don't look good
- The single SiPM channel 3 worked more or less Ok for early runs and
   had problems after run179. It behaved as if the constant DC was set
   on it. I will check whether it was a problem with the FADC or
   with the SiPM.


Cheers,
       Alex


P.S. I will send more plots with the time correlations shortly