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<div>The other issue that should be addressed is how pile up affects your ability to do PID. If you need to record a 10 mu s window and the hadronic rate is hundreds of kHz or even pushing 1 MHz (if I remember the numbers correctly 10^8 would something like
500 kHz but these predictions have large uncertainties) then you'll have multiple hadronic events in your recorded time window. </div>
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<div>Now, maybe this doesn't affect you due to occupancy still being low, etc, but I think it's worthy of at least addressing it. </div>
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<div>Mike</div>
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<div>
<div>On Sep 23, 2013, at 11:03 AM, "Curtis A. Meyer" <<a href="mailto:cmeyer@cmu.edu">cmeyer@cmu.edu</a>></div>
<div> wrote:</div>
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<blockquote type="cite">
<div>
Sorry that I missed the discussion on Friday, it sounds like it was interesting. One
<div>note on the 20KHz number that Lubomir mentioned. That is the expected rate off</div>
<div>level-1 at 10**7 photons per second. If we get to 10**8, then it will be at least 10</div>
<div>times this (hence the need for level 3 triggering). This may impact your ability to </div>
<div>wait for things - Curtis<br>
<div apple-content-edited="true">
<div>
<div>---------</div>
<div>Curtis A. Meyer
MCS Associate Dean for Faculty and Graduate Affairs</div>
<div>Wean: (412) 268-2745
Professor of Physics</div>
<div>Doherty: (412) 268-3090
Carnegie Mellon University</div>
<div>Fax: (412) 681-0648
Pittsburgh, PA 15213</div>
<div><a href="mailto:curtis.meyer@cmu.edu">curtis.meyer@cmu.edu</a>
<a href="http://www.curtismeyer.com/">http://www.curtismeyer.com/</a></div>
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<div>
<div>On Sep 23, 2013, at 9:58 AM, Beni Zihlmann <<a href="mailto:zihlmann@jlab.org">zihlmann@jlab.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">Hi All,<br>
I would like to clarify one point. Since I read out the modules on an <br>
event by event basis for each trigger the cpu(frontend) has to be <br>
interrupted by the trigger<br>
to read out the ADCs. It will take time for the cpu to react on this <br>
interrupt. I do not know how much but certainly many micro seconds. That <br>
is the reason I do<br>
not need to delay the trigger for the ADCs too much. I do not recall how <br>
much it is I will have to go back and measure it. I will let you know <br>
then then result.<br>
So by the time the actual readout command is executed by the roc the <br>
data has safely arrived at the ADCs.<br>
<br>
cheers,<br>
Beni<br>
<br>
<br>
<blockquote type="cite"><br>
Hi Matt,<br>
<br>
That was exactly the question Beni was asking when he started working <br>
on the DAQ for the cluster counting. Then he got it working right away <br>
without changing the timing of the trigger, as it was for the standard <br>
FDC readout. This means we were reading data from the fADCs that <br>
arrives up to 20 microseconds after the trigger. Beni can give you <br>
details about how and why does it work.<br>
<br>
Of course this is a simplified DAQ and there will be other limitations <br>
for the full GlueX DAQ. Naively I would think that if the maximal <br>
trigger rate is 20kHz (as I remember this is the official number) the <br>
readout rate should be the same, i.e. 50 microseconds per event which <br>
is 5 times more than the cluster counting time window. In any case I <br>
agree such a readout would be different from the rest of the detectors <br>
and we need to talk to the experts.<br>
<br>
Lubomir<br>
<br>
<br>
<br>
<br>
<br>
On Sat, 21 Sep 2013, Matthew Shepherd wrote:<br>
<br>
<blockquote type="cite"><br>
Hi Lubomir,<br>
<br>
After thinking about it more, I don't think I phrased my question in <br>
</blockquote>
the clearest way regarding the DAQ and cluster counting.<br>
<blockquote type="cite"><br>
You showed that you need to count ionization clusters that arrive over <br>
</blockquote>
a period of something 10 - 12 microseconds after the primary track.<br>
<blockquote type="cite"><br>
I think our trigger typically arrives 2-3 microseconds after the event. <br>
</blockquote>
For all subsystems this means they must look back into their buffer <br>
some fixed time and readout the event. (In many subsystems the <br>
trigger can't arrive much later or else the data is lost.)<br>
<blockquote type="cite"><br>
For the cluster counting scheme this means that you need retrieve data <br>
</blockquote>
from 2-3 microseconds before the trigger and up to 10 microseconds <br>
after the trigger. I don't understand the intricacies of the <br>
electronics or trigger, but does the fact that you won't have <br>
completely recorded an event until almost 10 microseconds after the <br>
trigger is sent to the crates cause a problem? (Presumably in that <br>
10 microseconds there is a decent probability that another trigger <br>
will arrive as well.)<br>
<blockquote type="cite"><br>
Maybe there is not a problem, but this seems to be a readout scheme <br>
</blockquote>
that is somehow fundamentally different from other subsystems.<br>
<blockquote type="cite"><br>
Matt<br>
<br>
---------------------------------------------------------------------<br>
Matthew Shepherd, Associate Professor<br>
Department of Physics, Indiana University, Swain West 265<br>
727 East Third Street, Bloomington, IN 47405<br>
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Office Phone: +1 812 856 5808<br>
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