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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Historical question: negative feedback and the op amp
References: <3DD25F72.5793B8D5@webaccess.net> <6PuA9.5701$XF5.email@example.com> <3DD27F3D.667A4D75@webaccess.net> <3DD2FD36.8877972F@webaccess.net> <3DD3A4A5.688DDDDD@webaccess.net> <3DD4635C.3E820E6C@webaccess.net> <3DD4FFD5.6CAC2E10@webaccess.net> <01c28dd2$e3ba9660$0100007f@stupidwin95> <3DD7B994.3E2AB7B0@webaccess.net> <3DD7BD84.9396F0BE@maine.rr.com>
Date: Sun, 17 Nov 2002 16:14:40 GMT
NNTP-Posting-Date: Sun, 17 Nov 2002 08:14:40 PST
"Raymond E. Rogers" wrote:
> Chuck Simmons wrote:
> > "Kevin G. Rhoads" wrote:
> > >
> > > >Remarkably little changes when you
> > > >substitute digital methods.
> > > Except that while a constant signal and a "bed of nails"
> > > have different Laplace transforms, they have identical
> > > z-transforms ;-) Too many people go to digital and
> > > forget they are now dealing with an inherently sampled
> > > system. The other side of "aliasing" is that you can't
> > > see what happens "during the holes".
> > > (Oversimplified, but I felt worth mentioning.)
> > Yes, I think of it as blind time. That is, the dynamical system can do
> > anything it wants and I won't see it. This is particularly messy in
> > digital systems where antialiasing filters are impossible (systems where
> > the sensor is inherenty sampled as in disk drive head positioning
> > servos). I have seen this so bad that it required mechanical redesign.
> My old sampled data systems box mentions using a "Modified Z transform"
> in order to peek between the samples during design. Is this just an
> idea that died? I have always managed to up the sample rate beyond the
> physics, but was going to use it if that couldn't be done.
The idea is still around. It really is something like an estimator. You
are using what you know about the dynamics to estimate what happens
between samples. If the dynamics are well known, the method will work
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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