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Re: Modeling and simulation



Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org> 

On Fri, 19 Sep 2003 21:18:01 -0600, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>

<snip>

>Some people try to optimize circuits using simulators, instead of
>designing them correctly from the start. This may work, but will not
>teach anything, and most probably will waste a lot of time.
>The site mentioned says that it's frequent to see a Spice simulation
>that works correctly, but an actual implementation that oscillates
>furiously. This is indeed a common problem, because it's difficult
>to include in the models (specially if the user has to do it) all
>the parasitic elements, and something that Spice does not consider,
>irradiation. Other than this, there is nothing wrong with the models
>used in Spice, that model the physical reality quite well.

My views regarding circuit simulation are the same as those regarding 
CAD/CAM and FEA: they are indeed a highly useful tool an engineer or 
designer can use to realize the end product.  But it takes correct models, 
input, and especially interpretation and correlation to realize a useful 
result.  A specific example is my first internship at P&H Mining Equipment 
in Milwaukee where I spent the better part of two months verifying that the 
output of a dynamic simulation model of one of their shovel's crawler drive 
system correlated to real world measurements.  That correlation process 
happens less and less frequently as engineers and designers are taught or 
learn to treat simulators as gospel.

That said, I don't recall seeing a Spice simulation of a coil that didn't 
correlate to measurements made on the actual system....  I also feel that 
the popular PSpice models (like the ones buried in Terry's site) are 
generally quite accurate if proper values are used.

Most the active components' spice models are woefully inadequate.  I wish I 
could cite specifics, but I really cannot since I really don't have any 
clue as to the internals of a SPICE model and really am just reciting what 
I've heard from scores of far more experienced SPICE users.

Regards,

Mark Broker
Chief Engineer, The Geek Group