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Re: TOF constant fraction



Hall D PID Mail List:

Beni,

See gluex doc GlueX Experiment Document 1211-v1.    This is the talk  
at the Jan. collaboration meeting.  The time walk was measured from  
-30mV to -1V.  The spread was 5.1 TDC counts which equals 286 ps.


Paul


http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=1211



On Jul 16, 2009, at 7:59 AM, Beni Zihlmann wrote:

> Hall D PID Mail List:
>
> Hi Sasha,
> thank you very much. While reading the manual I am not sure I like  
> this CFD ;-)
> First can you check what the delay settings are? According to the  
> manual the
> jumpers are set to 20ns by the factory. This would be far too much  
> for fast scintillator
> signals. It should be more like 4ns. This is the lowest possible  
> setting for this CFD
> unless your module is custom modified. (maybe 4ns is still too much  
> I do not know
> what the exact rise time of your signals are.)
> Also at some point it might be useful to check how good this CAEN  
> CFD really is.
> The manual has this sentence:
> "The maximum time walk is ±400 ps (for input signals in the range  
> from -50 mV to -
> 5 V with 25 ns rise time). "
> The number 400 really scares me. If this is really true this CFD is  
> useless.
> To check this you could use an ORTEC CFD model 935 or the older  
> module at lower
> bandwidth. They are very good CFD, they are NIM modules and have the  
> additional
> feature to adjust the zero cross over. With such a CFD and good  
> adjusted zero cross over
> the time walk is very very small, like for example 10ps or so (that  
> is a guesstimate).
>
> cheers,
> Beni
>
>
>> Hall D PID Mail List:
>>
>> On Wednesday 15 July 2009, Beni Zihlmann wrote:
>>
>>> Hall D PID Mail List:
>>>
>>> Hi Sasha,
>>> I could not find the document where the constant fraction is
>>> described. Can you again tell me what type of constant fraction you
>>> are using?
>>>
>>> thanks ,
>>> Beni
>>>
>>
>> Beni,
>>
>> We are using CAEN V812 CFD.   Further info is here:
>> http://www.caen.it/nuclear/product.php?mod=V812
>>
>> Sasha
>>
>
>

--
Prof. Paul Eugenio
Florida State University
Department of Physics
Tallahassee, Florida,  USA 32306

(850) 644-2585
eugenio@fsu.edu