<div dir="ltr">Alex,<div><br></div><div>| Actually fadc spectra for 1) and 3) agree reasonably well.</div><div>Yes, that is the problem. They agree on the FADC, but not on the scope.<br>
<br>| Why 2) is about 20% wider (was it a different readout channel)?</div><div>Because it runs through 100ft of cable, whereas 1 and 3 run through 50ft of cable. <br>
<br>| (there could be some sampling effects due to the different pulse<br>
| shape around the peak. I would also compare amps without the<br>| splitter).<br>
</div><div>I cannot remove the splitter because without it we have no FADC trigger. We need to split one of the signals to discriminate it. I agree there are details at the 10% level that relate to where the peak falls in the FADC clock. But the fall time is slow enough that this cannot be more than exp(-2ns / 16ns) ~ 12%. The FADC / scope discrepancy is much greater than that. See Fernando's email for the numbers.</div>
<div><br></div><div>-Richard J.</div><div><br></div></div><div class="gmail_extra"><br><br>
<div class="gmail_quote">On Wed, Feb 12, 2014 at 10:02 PM, Alexander Somov <<a href="mailto:somov@jlab.org">somov@jlab.org</a>> wrote:<br><blockquote class="gmail_quote">
<br>
Hello Richard,<br>
<br>
Actually fadc spectra for 1) and 3) agree reasonably well<br>
<br>
Why 2) is about 20% wider (was it a different readout channel)?<br>
<br>
(there could be some sampling effects due to the different pulse<br>
shape around the peak. I would also compare amps without the<br>
splitter).<br>
<br>
Cheers,<br>
Alex<div class="HOEnZb"><div class="h5"><br>
<br>
<br>
<br>
<br>
<br>
On Wed, 12 Feb 2014, Richard Jones wrote:<br>
<br>
<blockquote class="gmail_quote">
Dear colleagues,<br>
<br>
We are working to obtain light yields for the first article fiber bundle<br>
that was produced for the tagger microscope some time back. We have run<br>
into a problem trying to interpret what we see coming from the FADC250<br>
module that is installed in the data acquisition crate we are using for<br>
fiber QA tests. Please see the plots on the wiki page linked below that<br>
illustrate the problem we are seeing.<br>
<br>
<a href="https://halldweb1.jlab.org/wiki/index.php/Tagger_Microscope#Light_yield_tests">https://halldweb1.jlab.org/<u></u>wiki/index.php/Tagger_<u></u>Microscope#Light_yield_tests</a><br>
<br>
When we look at the signals on the scope, we see one set of amplitude<br>
ratios that clearly reveal the differences in light yield resulting from<br>
different lengths of the fibers that are covered in reflective paint. The<br>
results from the FADC are much less distinguished, and disagree in the<br>
ratios of pulse heights. Comments or suggestions as to what we are doing<br>
wrong would be appreciated.<br>
<br>
-Richard Jones<br>
<br>
</blockquote>
</div></div></blockquote></div><br></div>