Re: TOF constant fraction

[Beni Zihlmann <zihlmann@jlab.org>]

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
>