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Hi Fernando <br>
<br>
the point of lowering the gain was to increase the dynamic range so
we could accommodate<br>
a larger range of pulse heights (which was crucial for dE/dx). Based on
the noise that we were<br>
seeing, we carefully worked out that given the same noise and maximum
signal size,<br>
that a gain of 3 to 5 lower would allow us to do dE/dx except for the
extremely slow protons.<br>
If the maximum has actually decreased by a factor of two, then we have
effectively lost that<br>
in the dynamic range and I think that we probably have a problem with
this configuration.<br>
<br>
Curtis<br>
<br>
<br>
<br>
<br>
On 6/10/10 8:24 PM, Fernando J. Barbosa wrote:
<blockquote cite="mid:4C11823E.6050101@jlab.org" type="cite">Hi Naomi,
<br>
<br>
Now it makes sense. The original preamp had a gain of 1.5 mV/fC and the
new one that you have is 0.57 mV/fC. So, a factor of 2.63 lower now.
This seems to be confirmed on the first set of plots if you were to cut
the "overflows" from the left plot (just by looking at the plot).
<br>
<br>
The dynamic range on the old preamp was wider with 400 fC at the 1%
level; the new preamp is at 380 fC @ 5% (for your configuration). The
older preamp had a much wider DR with a smooth roll off before hard
saturation; the new preamp has narrower DR before hard saturation. It
is important to keep in mind that we want to operate in the linear
region, perhaps even better than the 5% level. This is seen on the next
sets of plots for the new preamp has a hard saturation at ~2100
channels. The fADC125 will be optimized to have this mapped to the
upper level of its 12-bit range.
<br>
<br>
I cannot say much about the energy plots because of non-linearity and
saturation on both old and new preamps. The detector gain is too high
and I suggest that you take additional runs starting at 1750V.
<br>
<br>
Thanks and best regards,
<br>
Fernando
<br>
<br>
<br>
<br>
<br>
Naomi Jarvis wrote:
<br>
<blockquote type="cite"><br>
Hello,
<br>
<br>
I just wanted to correct something I wrote yesterday (which did not
make sense anyway). From looking at the scope traces with the 55Fe
source I thought that the new preamp gain was less than that of the old
preamp. After actually collecting data and extracting amplitude
histograms it turned out that the preamp output was in fact saturating,
although I could not see this on the scope. I thought I could
distinguish between saturated and non-saturated traces, but evidently
this was not the case. So I have added some 55Fe plots to the wiki:
<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.jlab.org/Hall-D/software/wiki/index.php/Preamp_4:_Comparison_of_55Fe_data_with_original_preamp">http://www.jlab.org/Hall-D/software/wiki/index.php/Preamp_4:_Comparison_of_55Fe_data_with_original_preamp</a>
<br>
<br>
These are again comparing the two preamps, and to be clear, the only
difference between the two sets of runs is that the preamps are
switched and the baseline on the shaper is set to approx -130mV
(because the preamps have a different baseline). Everything else is
the same, both sets of data were taken on the same day.
<br>
<br>
Is there anything else you would like me to try with it tomorrow, or
leave counting over the weekend?
<br>
Naomi.
<br>
<br>
<br>
<br>
Fernando J. Barbosa wrote:
<br>
<blockquote type="cite">Hi all,
<br>
<br>
It seems that Monday @ 10 is preferable to most.
<br>
<br>
Gerard, I will discuss with you any issues related to the preamps and
ASICs afterwards.
<br>
<br>
In preparation for the meeting, I suggest reviewing GlueX docs 1070,
1079 and 1364. I will send an email with the agenda for the meeting by
the end of the week.
<br>
<br>
Thanks and best regards,
<br>
Fernando
<br>
<br>
Curtis A. Meyer wrote:
<br>
<blockquote type="cite">Monday at 10:00am would be great!
Curtis
<br>
On 6/9/10 2:31 PM, Fernando J. Barbosa wrote:
<br>
<blockquote type="cite">Hi Curtis,
<br>
<br>
Would Monday @ 10 next week work for everyone?
<br>
<br>
Best regards,
<br>
Fernando
<br>
<br>
<br>
<br>
Curtis A. Meyer wrote:
<br>
<blockquote type="cite">Hi Fernando
<br>
<br>
the next tracking meeting is not until June 23, so if we wait until
then to discuss this
<br>
issue, we will certainly fail to meet your deadline of June 25. It also
takes several days
<br>
of cosmic running to get a data point, so checking anything also takes
time. If there is any
<br>
way that we could have a meeting next week, it would help speed things
along.
<br>
<br>
thanks - Curtis
<br>
<br>
<br>
On 6/9/10 12:55 PM, Fernando J. Barbosa wrote:
<br>
<blockquote type="cite">Hi Naomi,
<br>
<br>
I suggest we reserve part of the next tracking meeting to discuss these
issues.
<br>
<br>
Let me also take the opportunity to emphasize that the CDC and the FDC
groups must finalize their measurements so that the procurement of the
ASICs is not impacted. This means that I would like to close this
project by 25 June 2010.
<br>
<br>
Thanks and best regards,
<br>
Fernando
<br>
<br>
<br>
Naomi Jarvis wrote:
<br>
<blockquote type="cite"><br>
Good morning!
<br>
<br>
I would like to talk about the new preamp but I don't think there will
be enough time in our tracking mtg this morning.
<br>
The concerns are that the preamp output is topping out at around 500 mV
even with the cosmics, and the gain for cosmics seems to have
increased, whereas for Fe55 it was ~1/3 less.
<br>
<br>
I put one page on the wiki
<a class="moz-txt-link-freetext" href="http://www.jlab.org/Hall-D/software/wiki/index.php/CDC#Preamp4_.28GlueXdoc1364_Tbl_2_Row_2.29">http://www.jlab.org/Hall-D/software/wiki/index.php/CDC#Preamp4_.28GlueXdoc1364_Tbl_2_Row_2.29</a>
<br>
The recent cosmic runs there took a week each, and were with the
chamber flat, ie 90 degree cosmics. I'll add more data as it becomes
available; at present it is counting at 2kV.
<br>
Can we set up a time to talk about this next week? (The rest of this
week is out for us; I think the only times we cannot do next week are
1pm Tues + the regular mtg on Wed).
<br>
<br>
Thanks,
<br>
<br>
Naomi.
<br>
</blockquote>
</blockquote>
<br>
<br>
</blockquote>
</blockquote>
<br>
<br>
</blockquote>
</blockquote>
<br>
</blockquote>
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<pre class="moz-signature" cols="72">--
Prof. Curtis A. Meyer Department of Physics
Phone: (412) 268-2745 Carnegie Mellon University
Fax: (412) 681-0648 Pittsburgh PA 15213-3890
<a class="moz-txt-link-abbreviated" href="mailto:cmeyer@ernest.phys.cmu.edu">cmeyer@ernest.phys.cmu.edu</a> <a class="moz-txt-link-freetext" href="http://www.curtismeyer.com/">http://www.curtismeyer.com/</a>
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