[Halld-tracking-hw] old preamp

[Curtis A. Meyer]

Hi Everyone -

      Naomi's most recent post is a comparison of how our OLD 
preamplifier behaved
more than 4 months ago versus how it (the OLD one) is behaving now. The 
only conclusion
that one can draw is the our OLD preamp "bit the dust". Its gain has 
gone up by at least a
factor of 4 and there is substantial noise beyond what we used to 
observe. In the top-right
plot of that page (Fe-55) the peak at channel ~800 is this new noise 
which is seen as an
oddly-shaped 200-mV pulse.

       That all said, what it implies is that the comparison 
measurements that we took (recently)
between the old preamplifier and the new one are not meaningful. Because 
the old one is
no longer performing correctly, it makes no sense to compare the new 
preamplifier with it.

       This means that we need to go back to the data that were 
collected (as input to our paper)
to make comparisons. There, we only have Fe-55 at about 2100 V, which 
was saturating
the old preamplifier and would be so off scale in the new one, that no 
comparison makes sense.

       We do have cosmic data at a number of settings with the old 
preamplifier from before, and
all of these show that the gain of the new preamplifier is larger than 
the old one. We are now
undertaking a set of measurements to determine the efficiency curve (vs 
HV) for the new preamplifier.
We already know that it needs to run at least 200V lower than the old 
one, but we will get the
correct operating point and then try to determine if the dynamic range 
is sufficient for the
CDC.

       It would also help if there were another old preamplifier that we 
could use. It would allow
us to make the Fe-55 measurements which can be more directly compared. 
Thus, our request for
an old card.

          Curtis
On 6/24/10 7:59 AM, Beni Zihlmann wrote:
> Hi Naomi,
> the last four plots in
> http://www.jlab.org/Hall-D/software/wiki/index.php/CDC_old_preamp_then_and_now
> are all old preamp card plots and the the "new" is just a typo (right?).
> If this is a correct assumption then the plots would be also compatible
> if the dynamic range of the ADC
> is changed by a factor of 5 in the amplitude. The cosmic peak is at
> around channel 300 in the older data and in the latest
> data around 1500 (if that assumption is correct). This would give a
> factor of 5 smaller dynamic range of the ADC in terms
> of amplitude decoded in 12 bits.
> Could that be the case?
>
> cheers,
> Beni
>
>
>    
>> Hi Fernando,
>>
>> it looks like our old preamp is no longer working properly... see
>>
>> http://www.jlab.org/Hall-D/software/wiki/index.php/CDC_old_preamp_then_and_now
>>
>> (The spike in the amplitude plot at 800ch is some nasty noise which appeared around 2 weeks ago).
>>
>> By any chance do you have another one that we could use?
>>
>> Best regards,
>>
>> Naomi.
>> _______________________________________________
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>> https://mailman.jlab.org/mailman/listinfo/halld-tracking-hw
>>
>>      
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>    


-- 
Prof. Curtis A. Meyer		Department of Physics
Phone:	(412) 268-2745		Carnegie Mellon University
Fax:	(412) 681-0648		Pittsburgh PA 15213-3890
cmeyer at ernest.phys.cmu.edu	http://www.curtismeyer.com/