Math Problem

[rsocor01]

Erice1984,

You can do a linear approximation but you are going to loose accuracy. Try doing a polynomial or exponential approximation. In EXCEL go to help and see how to add a trendline (it varies with the different versions of EXCEL). Obtaining the trendline is very simple. The trendline is going to give you a formula in the form of Y(X), X being the temperature and Y being the Resistance. Try with different options and settings until you get a good approximation. Then, you can use the resulting formula in your PBP program. That is with any value X (temperature) you can calculate a value Y (resistance).

You should get the whole temperature range 100-250 degrees F in your graph before doing an approximation, so you get better results.

This is one way to do it, which is very accurate. It all depends on the accuracy that you want for the resistance reading.

Hope that this helps.

Robert

[erice1984]

Thank you very much!

Wow, that was really easy!

I lost accuracy but its in the place I don't care about!

[mister_e]

I already used the following with good results.

Curve Expert
http://userpages.xfoneusa.net/~dhyams/cmain.htm

[erice1984]

It all works, just wondering how I will try to make exponents happen..

[mister_e]

What's your current formula?

A third degree polynomial didn't fit?

[erice1984]

f(x) = 5167.68(0.98^x)

[mister_e]

could be more simple than you think
http://en.wikipedia.org/wiki/Exponentiation

[mister_e]

Nope, bad link...

[erice1984]

well, I changed it up and am using three diff power curves to keep everything within 1 degree +/-

only thing that is trouble is negative exponents.. tryin to figure out how to simplify it out so pbp can do it, but im am sucking on figuring this out. lol

[mister_e]

You could still build a lookup table and use some interpolation between some points, that should do the trick and way easy to implement.