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'[EE]: Why Steinhart-Hart equation...?'
2001\04\19@095713 by Jose S. Samonte Jr.

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Hello to all! =)
In my project, I've used the Steinhart-Hart equation to linearize the output
of the thermistor, because I have found out that it is the most commonly used.
But my professor wants a much better reason why I used
Steinhart-Hart equation. What could be much better reasons, why Steinhart-Hart
equation? He said that there are other equations that could be used. Are
there? Please help me.

Thank you very much and God Bless.
Best regards.



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2001\04\19@101627 by Eisermann, Phil [Ridg/CO]

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The Steinhart-Hart equation DOES NOT linearize the the output of a
thermistor. It is really a curve-fitting function for resistance vs.
temperature. Put another way, it is a mathematical model of the thermistor's
behavior in response to temperature. The reason that people like to use it
is because it is an extremely accurate model over a very wide range of
temperature.

{Original Message removed}

2001\04\19@105108 by Scott Dattalo

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On Thu, 19 Apr 2001, Jose S. Samonte Jr. wrote:

> Hello to all! =)
> In my project, I've used the Steinhart-Hart equation to linearize the output
> of the thermistor, because I have found out that it is the most commonly used.
> But my professor wants a much better reason why I used
> Steinhart-Hart equation. What could be much better reasons, why Steinhart-Hart
> equation? He said that there are other equations that could be used. Are
> there? Please help me.

Tell your professor that you use S-H because everyone else does, but after
becoming an experienced PIC programmer you've discovered that a look up table
with first order interpolation is the best way to "linearize" a thermistor with
a microcontroller.

He'll say , "True, but why?"

And you'll say, "Well Sir, it's obvious. With the S-H approach you have to
compute these really nasty logarithms and arithmetic operations. All of that
just to get 1 or 2% accuracy. However with a lookup table it only takes about 20
CPU cycles to get an answer that's accurate to with in a 0.5%. However, I found
that the look up table can only give you this accuracy after the thermistor has
been carefully calibrated. In other words, with the S-H equation I found my
compuatations suffered from cumulative round off errors but the look-up table is
accurate as the data in the table."

"Hmm. 20-cycles for 0.5% accuracy? Amazing! How did you do that?"

"Sir, I only tell you if you give me an A+."


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What do you think, Jose? Will he like that?


Scott

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2001\04\19@105925 by Alan B. Pearce

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>"Hmm. 20-cycles for 0.5% accuracy? Amazing! How did you do that?"

>"Sir, I only tell you if you give me an A+."



ROTFL

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