<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix">Hi Richard,<br>
<br>
The fADC250 has a linearity of ~1% full scale and also a ch-to-ch
gain variation of 1%. We measured these before and during
production with pulses and levels. There is no processing at all
in raw data mode. Your signals are so close in amplitude and so
far away from saturation that I doubt there is any non-linearity
effects, other the edge speed and sampling as I mentioned earlier.
You can easily check this with a ramp signal or a precision
variable attenuator.<br>
<br>
I would check with another scope channel and another ADC channel
to be sure there are no inconsistencies.<br>
<br>
Best regards,<br>
Fernando<br>
<br>
<br>
On 2/13/2014 1:01 AM, Richard Jones wrote:<br>
</div>
<blockquote
cite="mid:CABfxa3Rk2qiS+Br4v6C2Q992jn6eAMgBA73Ug-xrD=cPhjG10g@mail.gmail.com"
type="cite">
<div dir="ltr">Fernando,
<div><br>
</div>
<div>We cannot use the scope for these tests because we can only
see a few channels at a time. We would very much like to
understand the DAQ so we can move on and start fiber QA
studies. The decay time of these signals is so slow that the
rise time will not affect the max pulse height by more than
about 10%. Running the signals shown on the scope through a
125MHz low-pass filter reduces the pulse height somewhat, but
does not affect the ratios. There are variations based on the
exact delay through each channel and the FADC clock, but these
effects are +/- 10% because of the slow decay time. As you
state, we are comparing ratios of 40% on the scope and 15% on
the ADC. </div>
<div><br>
</div>
<div>We do not show the pictures on the wiki, but if we swap the
inputs on the FADC, the results do not change by more than a
couple percent. This shows that it cannot be gain variations
between the different channels on the FADC, but must be some
kind of signal processing that is doing very different things
to the peak heights depending on what preamp output generated
them. Is there possibly some nonlinear processing of the raw
FADC values that is happening in the module before we see
them? As Alex points out, the pulse shapes of channels 1 and
3 are virtually identical, but the ratio of their amplitudes
disagrees: 6% on the FADC vs 20% on the scope.</div>
<div><br>
</div>
<div>-Richard J.</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Thu, Feb 13, 2014 at 12:16 AM,
Fernando J. Barbosa <<a moz-do-not-send="true"
href="mailto:barbosa@jlab.org">barbosa@jlab.org</a>>
wrote:<br>
<blockquote class="gmail_quote">Hi Richard,<br>
<br>
From the pictures, I get for each set the following peak
amplitudes:<br>
1) 64mV, 278 channels=4.3 ch/mV<br>
2) 46mV, 248 ch=5.4 ch/mV<br>
3) 76 mV, 295 ch=3.9 ch/mV<br>
<br>
Clearly not linear where a 40% change on the scope
corresponds to 16% on the ADC. This is because we are
looking at peak values and the pulse rise time is less than
4ns (ADC sampling). If you are triggering the ADC from the
laser pulser, try adding cables in 1ns increments to see how
the ADC amplitude changes. The pulse risetime is just too
fast for the ADC to sample properly (must be > 4ns).
Because the pulse duration is much longer than the pulse
risetime, charge should be OK as it is to be used in the
experiment. The scope is the better tool for your tests of
the fibers unless you put a low pass filter to increase the
pulse risetime.<br>
<br>
Best regards,<br>
Fernando<br>
<div>
<div class="h5"><br>
<br>
<br>
<br>
----- Original Message -----<br>
From: Alexander Somov <<a moz-do-not-send="true"
href="mailto:somov@jlab.org">somov@jlab.org</a>><br>
To: Richard Jones <<a moz-do-not-send="true"
href="mailto:richard.t.jones@uconn.edu">richard.t.jones@uconn.edu</a>><br>
Cc: Hall D beam working group <<a
moz-do-not-send="true"
href="mailto:halld-tagger@jlab.org">halld-tagger@jlab.org</a>><br>
Sent: Wed, 12 Feb 2014 22:02:13 -0500 (EST)<br>
Subject: Re: [Halld-tagger] first results on fiber light
yields<br>
<br>
<br>
Hello Richard,<br>
<br>
Actually fadc spectra for 1) and 3) agree reasonably
well<br>
<br>
Why 2) is about 20% wider (was it a different readout
channel)?<br>
<br>
(there could be some sampling effects due to the
different pulse<br>
shape around the peak. I would also compare amps without
the<br>
splitter).<br>
<br>
Cheers,<br>
Alex<br>
<br>
<br>
<br>
<br>
<br>
On Wed, 12 Feb 2014, Richard Jones wrote:<br>
<br>
> Dear colleagues,<br>
><br>
> We are working to obtain light yields for the first
article fiber bundle<br>
> that was produced for the tagger microscope some
time back. We have run<br>
> into a problem trying to interpret what we see
coming from the FADC250<br>
> module that is installed in the data acquisition
crate we are using for<br>
> fiber QA tests. Please see the plots on the wiki
page linked below that<br>
> illustrate the problem we are seeing.<br>
><br>
> <a moz-do-not-send="true"
href="https://halldweb1.jlab.org/wiki/index.php/Tagger_Microscope#Light_yield_tests">https://halldweb1.jlab.org/wiki/index.php/Tagger_Microscope#Light_yield_tests</a><br>
><br>
> When we look at the signals on the scope, we see
one set of amplitude<br>
> ratios that clearly reveal the differences in light
yield resulting from<br>
> different lengths of the fibers that are covered in
reflective paint. The<br>
> results from the FADC are much less distinguished,
and disagree in the<br>
> ratios of pulse heights. Comments or suggestions as
to what we are doing<br>
> wrong would be appreciated.<br>
><br>
> -Richard Jones<br>
><br>
</div>
</div>
_______________________________________________<br>
Halld-tagger mailing list<br>
<a moz-do-not-send="true"
href="mailto:Halld-tagger@jlab.org">Halld-tagger@jlab.org</a><br>
<a moz-do-not-send="true"
href="https://mailman.jlab.org/mailman/listinfo/halld-tagger">https://mailman.jlab.org/mailman/listinfo/halld-tagger</a><br>
<br>
</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</body>
</html>