[Halld-tracking-hw] ADC125 as a TDC...

[Beni Zihlmann]

I forgot to mention:
Always the first and the last channel of a preamp have some tail.
This is an edge effect when the edge strip is not the center of the
cluster I guess but rather the upper and lower edge respectively
and given only one strip hit for this event.

cheers,
Beni


> Hi Gerard,
> thanks for the idea. I took only the fastest trip for each preamp card.
> had here the result. This cleans up the spectra dramatically. Also you
> can see that for a given card the timing seems to drift for groups of
> strips. In particular strip 1 ot 24 you see a distinctive wiggle.
>
> cheers,
> Beni
>
>> Hi Beni,
>>     I'm not sure what to make of that tail either. One question that 
>> might be
>> related: are you putting a point on the histogram for every strip? 
>> What would it
>> look like if you just used the earliest strip hit? Certainly the side 
>> strips
>> which see smaller signal will not cross the timing threshold as soon 
>> as the
>> central strip(s) do. That effect must produce a tail to the left in 
>> this plot,
>> but whether it would be such an extreme tail, I don't have a clue.
>>     Have you had an opportunity to begin to optimize the LE 
>> threshold? (I'm still
>> guessing this would mainly be done with a goal of overall drift 
>> coordinate
>> resolution, so maybe that has to wait a bit. But on the other hand 
>> also would
>> worry that all results are threshold dependent and is it set roughly 
>> where we
>> will want it?)
>>     Sincerely,
>>
>>         Gerard
>>
>> On 5/17/2011 8:20 AM, Beni Zihlmann wrote:
>>> Hi All,
>>> attached are 3 plots. The first is a 2d plot for FDC wire 11 on cosmic
>>> data. The vertical axis is the strip number and the horizontal axis
>>> is the time difference between the strip and wire 11. The times are
>>> determined using Gerard's algorithm with interpolation on the FDC
>>> data for both the wire and the strip. Note that the time difference
>>> is calculated as "t_wire - t_strip" so the long tail to the negative 
>>> times
>>> is due to the strip while we have a rather sharp edge on the right 
>>> side.
>>> this can be seen more clearly when looking at the projection of the 2d
>>> plot to the horizontal axis. This is shown in the next to plots 
>>> individually
>>> for the channel 0-23 and 24-47 which represents the two preamp cards
>>> for the top and bottom cathode planes. I try to extract a width by 
>>> fitting
>>> mostly only the upper edge. As you can see the width is between 1 and
>>> 1.5 ns. So the individual resolution may be about sqrt(2) better. 
>>> You can
>>> also see that the timing resolution depends on the average signal 
>>> amplitude
>>> which is smaller for the second preamp (channel 24-47). I do not 
>>> know what
>>> causes the shift in time between the two preamp card. This shift is 
>>> certainly
>>> much larger than any cable length miss match etc. But Lubomir observed
>>> this behavior already earlier.
>>> What causes the long tail to negative time difference is not 
>>> completely clear
>>> to me. One reason might be that there are considerable gain 
>>> variations between
>>> strip channels and I plot all hits not just the one with the largest 
>>> amplitude
>>> in a hit.
>>> Let me know if you have additional ideas what else one could tests.
>>>
>>> cheers,
>>> Beni
>> _______________________________________________
>> Halld-tracking-hw mailing list
>> Halld-tracking-hw at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw
>
>
> _______________________________________________
> Halld-tracking-hw mailing list
> Halld-tracking-hw at jlab.org
> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://mailman.jlab.org/pipermail/halld-tracking-hw/attachments/20110517/f195c835/attachment.html