[Halld-tagger] first results on fiber light yields

[Beni Zihlmann]

Hi Richard,

the division in time is 10ns for the scope if I read the picture 
correctly. So the change in peak amplitude
is much faster than the 4ns sampling rate of the FlashADC. As a result 
the flashADC is a very poor tool
to be use as a peak sensing adc. I think you need to integrate the 
signal to get results that you can compare.

my half cent input,

Beni

> Dear colleagues,
>
> We are working to obtain light yields for the first article fiber 
> bundle that was produced for the tagger microscope some time back.  We 
> have run into a problem trying to interpret what we see coming from 
> the FADC250 module that is installed in the data acquisition crate we 
> are using for fiber QA tests.  Please see the plots on the wiki page 
> linked below that illustrate the problem we are seeing.
>
> https://halldweb1.jlab.org/wiki/index.php/Tagger_Microscope#Light_yield_tests
>
> When we look at the signals on the scope, we see one set of amplitude 
> ratios that clearly reveal the differences in light yield resulting 
> from different lengths of the fibers that are covered in reflective 
> paint.  The results from the FADC are much less distinguished, and 
> disagree in the ratios of pulse heights.  Comments or suggestions as 
> to what we are doing wrong would be appreciated.
>
> -Richard Jones
>
>
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