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Re: Cross talk
Hi Fernando,
About the cross talk: yes of course, but at least the plots show that
something is going on. I need to run over the data again for the scatter
and that takes some time. The plots I showed I had already available.
For the peak amplitude plots I go over the fADC time spectra and take the
time sample with the maximum ADC value. I (my program) subtract the
pedestal mean (650) of this (ADC) value and if it is above pedsigma*5 it
is dumped into the peak-amplitude histogram. I do this for every event. By
changing the pedestal (threshold cut) the amplitude distribution shape
will not change, you will only add/cut away the lowest peak-amplitudes but
I can do it anyway.
I do not understand your proposition to make a coincidence between two
adjacent straws. The Fe-55 source is collimated (2*r = 0.5mm) in order to
keep the rate down (the VME computer crashes when the rate is higher then
30 events/s) I could point it to a region where two straws are overlapping
but do you really expect coincidences? I would think the x-ray is
completely absorbed in one or the other straw, not in both. I believe you
can also see this in the cross talk plots on the wiki: the source is
placed on channel 2 but also pointing to channel 5. The trigger is on
channel 2 and I do not see something in channel 5.
Cheers,
Yves
/--------------------------------
/ Yves Van Haarlem
_--~~--_ /
/~/_| |_\~\ / Carnegie Mellon University
|____________| / Department of Physics
|[][][][][][]|:= / Wean Hall room 8404
__| __ |__ \ Pittsburgh, PA 15213
| ||. | == | | \ USA
(| ||__| == | |) \
| |[] [] == | | \ Tel.: +1 412 268-6949
| |____________| | \ +1 412 641-9252
/__\ /__\ \ Fax.: +1 412 681-0648
~~ ~~ \-----------------------------------
On Thu, 19 Jun 2008, Fernando J. Barbosa wrote:
> Hi Yves,
>
> I looked at the plots you just posted and I have a few questions.
>
> For crosstalk, you are plotting the peak amplitude distributions for the
> whole data run, I believe. You need to compare the peak amplitudes on an
> event-by-event basis, e.g., compare peak amplitude on ch1 to ch2 for event 1,
> and repeat for the other events. The best way to do this is to get a scatter
> plot. Applying a fit to the scatter plot, should yield a straight horizontal
> line (or vertical) [meaning independence between channels] for zero crosstalk
> or a line with a slope for any crosstalk. The slope is the crosstalk, say
> volts in ch1 to volts in ch2. You will need a plot for each channel adjacent
> to the straw with the source.
>
> For the raw ADC data, one event per plot, it seems that the noise is very low
> and that is a good thing. Now, when you take this data and plot the amplitude
> distribution do you apply a threshold cut? For instance, I see that the
> baseline or pedestal is at about ADC channel 650 - do you exclude all the
> samples below this value? It would also be interesting to see how the
> amplitude distributions change with different threshold cuts.
>
> For the "energy" plots, it seems that these plots follow the same trend as
> those plots under "Different-HV" which is good. But I still don't understand
> why the shape - it should look like a Poisson distribution or more properly a
> Landau distribution. What I see is that the low level amplitude tail gets
> proportionally smaller with increasing HV, as a result of perhaps higher S/N
> ratio. This may be artificial, of course, due to higher occurrence of limited
> streamer pulses or higher gain (more signals above the trigger threshold).
>
> It would be nice if you could form a trigger by using the coincidence of two
> overlapping straws, as I mentioned in a previous email.
>
> Regards,
> Fernando
>
>
>
>
> Yves Van Haarlem wrote:
>> Hi All,
>>
>> As a follow up from the meeting this after noon. I posted some
>> peak-amplitude spectra on the wiki concerning cross talk. One can see that
>> there is some measurable electronic cross talk between adjacent channels on
>> the HV-board.
>>
>> http://www.jlab.org/Hall-D/software/wiki/index.php/ASIC_design_optimizations#Cross_talk
>>
>>
>> Cheers,
>> Yves
>>
>> /--------------------------------
>> / Yves Van Haarlem
>> _--~~--_ /
>> /~/_| |_\~\ / Carnegie Mellon University
>> |____________| / Department of Physics
>> |[][][][][][]|:= / Wean Hall room 8404
>> __| __ |__ \ Pittsburgh, PA 15213
>> | ||. | == | | \ USA
>> (| ||__| == | |) \
>> | |[] [] == | | \ Tel.: +1 412 268-6949
>> | |____________| | \ +1 412 641-9252
>> /__\ /__\ \ Fax.: +1 412 681-0648
>> ~~ ~~ \-----------------------------------
>>
>