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Re: shaper gain
On Tue, 29 Jul 2008, Elton Smith wrote:
Dear all,
I think we have to be a bit careful. If you want to do PID you want to
have your information as accurate as possible. And a non linear scale
might impact this, because you compress your information more. This might
wash out differences you would in a linear scale see.
I would advise to look into this a bit more before taking a decission.
bye elke
> Date: Tue, 29 Jul 2008 08:00:37 -0400 (EDT)
> From: Elton Smith <elton@jlab.org>
> To: Curtis A. Meyer <cmeyer@ernest.phys.cmu.edu>
> Cc: Gerard Visser <gvisser@indiana.edu>,
> Fernando J. Barbosa <barbosa@jlab.org>, Elton Smith <elton@jlab.org>,
> FDC email list <halld-tracking-hw@jlab.org>
> Subject: Re: shaper gain
>
>
> Hi Curtis and Gerard,
>
> Clearly the ADC and the ASIC outputs should match as best as possible. But
> my comment is related to the non-linear region, if required, in the
> data. The main purpose for the dE/dx measurements is to identify protons
> (distinguish them from pions). For this, we simply need to have pulse
> height outputs that are different for the two cases, and a non-linear
> scale may be fine. In other words, non-linear "corrections" per se may not
> be needed, as we are not trying to determine the precise value of energy
> loss, simply checking differences between two particle types.
>
> Cheers, Elton.
>
>
>
>
>
> Elton Smith
> Jefferson Lab MS 12H5
> 12000 Jefferson Ave
> Suite # 16
> Newport News, VA 23606
> elton@jlab.org
> (757) 269-7625
> (757) 269-6331 fax
>
> On Mon, 28 Jul 2008, Curtis A. Meyer wrote:
>
> > Hi Gerard -
> >
> > thanks for the comment on the ADC range. I am not sure what we need to
> > do, but it would certainly be better to match as much of the linear range
> > of the ASIC to that of the Flash-ADC. While we can probably correct for
> > the lon linear part as we move above the charge limit, I suspect that those
> > corrections are probably temperature dependent. While this may not be
> > a problem, we probably want to think about this up front.
> >
> > Curtis
> > On Mon July 28 2008, Gerard Visser wrote:
> > > Hi Fernando,
> > > Oh, one other point, and this is maybe worthwhile for others to
> > > consider too. The present "anode" setup of the shaper board, I believe,
> > > puts the full scale of the ADC at roughly 770 fC (instantaneous input
> > > charge, e.g. Fe55), as documented on page 2 of
> > > http://argus.phys.uregina.ca/gluex/DocDB/0007/000736/003/Receiver_Shaper_Setup_for_GPC01.pdf
> > > In other words, the "good linear range" of the ASIC is presently about
> > > 39 to 52% of the ADC range, depending on what you call "good".
> > > With the proposed change, the "good linear range" of the ASIC should
> > > then be about 8 to 10 % of the ADC range. I'm not sure this is really
> > > what we want to do... (Although of course we can try it and see. I could
> > > be proved wrong!)
> > >
> > > Gerard
> > >
> > > Gerard Visser wrote:
> > > > Hi Fernando,
> > > > Ok, just to check, this will be setting the gain 1/5 of the present
> > > > "anode" shaper gain, is that correct? (If not, please say...)
> > > ...
> > >
> >
> >
> >
> > --
> > Professor Curtis A. Meyer Department of Physics
> > Phone: (412) 268-2745 Carnegie Mellon University
> > Fax: (412) 681-0648 Pittsburgh PA 15213-3890
> > cmeyer@ernest.phys.cmu.edu http://www.curtismeyer.com/
> >
>
>
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