topic Re: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ? in LabVIEW
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355339#M986667
<P>I have not looked at your VI.</P><P> </P><P>Any fitting process needs to start with an appropriate function. To get that you need to look at the physics of your system - in this case a thremistor. A simple search will show that the resistance-temperature relationship is not at all a polynomial. Specifically, the Steinhart-Hart equation is often used.</P><P> </P><P>You may be able to fit the 3 parameters of that equation to your data table using Lev-Mar or something similar.</P><P> </P><P>Lynn</P>Thu, 06 Oct 2016 15:41:30 GMTjohnsold2016-10-06T15:41:30ZHow to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355335#M986665
<P>I have the datasheet from a NTC (Negative Thermistor Coefficient) and I want to calculate the most approximate equation</P><P>that describes it's behaviour. The table has temperature and resistance values. So the resistance of the NTC varies depending on the temperature it detects. I've already tried the next:</P><P> </P><P>- Excel: polynomial fitting</P><P>- Maple: polynomial fitting</P><P>- LabVIEW: Polynomial Fit.vi</P><P> </P><P>I've been getting equations with a not very good approximate parameteres. I'm suspecting that this method "polynomial FIT" it's not the best method for this type of data/equation (being a nonlinear equation). </P><P> </P><P>So has someone used the Nonlinear Fit.vi to approximate the behaviour of a dataset? If so, can you explain me how this VI works... I would really appreciate it.</P><P> </P><P>Thanks in advance and I'll wait for your answer.</P><P> </P><P> </P><P> </P>Thu, 06 Oct 2016 15:34:25 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355335#M986665JLuna2016-10-06T15:34:25ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355339#M986667
<P>I have not looked at your VI.</P><P> </P><P>Any fitting process needs to start with an appropriate function. To get that you need to look at the physics of your system - in this case a thremistor. A simple search will show that the resistance-temperature relationship is not at all a polynomial. Specifically, the Steinhart-Hart equation is often used.</P><P> </P><P>You may be able to fit the 3 parameters of that equation to your data table using Lev-Mar or something similar.</P><P> </P><P>Lynn</P>Thu, 06 Oct 2016 15:41:30 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355339#M986667johnsold2016-10-06T15:41:30ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355377#M986684
<P>Hi JLuna,</P><P> </P><P>could you convert your VI to LV2014 and attach this version too? (This would allow me and others to actully examine your VI.)</P><P> </P><P>Another approach, most often very easy with good results:</P><P>Put the resistance-temperature pairs into an array of points. Then use Interpolate1DArray to get the temperature from resistance reading:</P><P><IMG src="https://forums.ni.com/t5/image/serverpage/image-id/189889i2168FC7394621557/image-size/original?v=v2&px=-1" border="0" alt="check.png" title="check.png" /></P><P>(Replace my dummy data with you real data!)</P><P> </P><P>One more approach: with NTC thermistors you usually get R0 and B values from datasheet. Then <A href="https://en.wikipedia.org/w/index.php?title=Thermistor&action=edit&section=3" target="_self">apply the formulas</A> described at Wikipedia!</P>Thu, 06 Oct 2016 17:06:41 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355377#M986684GerdW2016-10-06T17:06:41ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355378#M986685
<P>i've just read about this equation. I didn't have notion of it's existance. Apparently it has 3 coefficients that can be</P><P>calculated. In your post you mention:</P><P> </P><P>"You may be able to fil 3 parameters of that equation to your data table using Lev-Mar or something similar".</P><P> </P><P>And by "3 parameters" you mean, the coefficients that are needed to be calculated. If I'm interpretating this right, there</P><P>is a Nonlinear vi, that uses the method Lev-Mar. In this VI, it has an input called "initial parameters": Is this input referring to this parameters?</P><P> </P><P>**I've never used this type of VI's so I'm having lots of questions...</P><P> </P><P>Thanks for your answer!!</P><P> </P><P> </P><P> </P><P> </P>Thu, 06 Oct 2016 17:07:47 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355378#M986685JLuna2016-10-06T17:07:47ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355385#M986689
<P>Here is the 2014 version. I'll try that interpolating also... I'm a bit skeptical, because the "Interpolate 1D array"mentions to linearize the "y"values from your "x" values. But I'll give that a try also.</P><P> </P><P>I just want to calculate en equation with a very low error. I dunno maybe at most, 2% error.</P><P> </P><P>Thanks for your answer.</P>Thu, 06 Oct 2016 17:28:20 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355385#M986689JLuna2016-10-06T17:28:20ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355403#M986695
<P>A higher order polynomial is a nonlinear fit. If you use more normal fit option (just delete these misquided "bisquare" and "SVD for rank defficient ..." inputs!) and things look much better!</P>Thu, 06 Oct 2016 18:14:00 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355403#M986695altenbach2016-10-06T18:14:00ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355404#M986696
<BLOCKQUOTE><HR /><LI-USER uid="7614"></LI-USER> wrote:<BR /><P>A higher order polynomial is a nonlinear fit. If you use more normal fit option (just delete these misquided "bisquare" and "SVD for rank defficient ..." inputs!) and things look much better!</P><HR /></BLOCKQUOTE><P>Here is a 6th order polynomial fit to the two datasets leaving the optional inputs disconnected. Seems good enough.</P><P> </P><P><IMG src="https://forums.ni.com/ni/attachments/ni/170/986696/2/PolynomialFits.png" border="0" alt="" title="" /></P><P> </P>Thu, 06 Oct 2016 18:25:41 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355404#M986696altenbach2016-10-06T18:25:41ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355406#M986697
<P>But yes, if there is a suitable mathematical model with fewer paramters, you should use nonlinear fit.</P>Thu, 06 Oct 2016 18:22:34 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355406#M986697altenbach2016-10-06T18:22:34ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355408#M986698
<P>Can you display the six order equation for those two graphics.</P><P> </P><P>I generated several equations using "Polynomial Fit" and using the calculated equations I substitute a new value of my choice, for</P><P>example 23.2. And watched how this equation delivered a similar value to the graphic. So, can you display the equations please?</P><P> </P>Thu, 06 Oct 2016 18:27:54 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355408#M986698JLuna2016-10-06T18:27:54ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355411#M986699
<P>The equations are polynomials and the coefficients I found were:</P><P> </P><P><FONT face="terminal,monaco" size="2">32080.3 </FONT><BR /><FONT face="terminal,monaco" size="2">-1484.52 </FONT><BR /><FONT face="terminal,monaco" size="2">48.3516 </FONT><BR /><FONT face="terminal,monaco" size="2">-1.35193 </FONT><BR /><FONT face="terminal,monaco" size="2">0.0224839 </FONT><BR /><FONT face="terminal,monaco" size="2">-0.000180263 </FONT><BR /><FONT face="terminal,monaco" size="2">5.39565E-7</FONT></P><P> </P><P>and for the lower set:</P><P> </P><P><FONT face="terminal,monaco" size="2">32080.3 </FONT><BR /><FONT face="terminal,monaco" size="2">-1484.52 </FONT><BR /><FONT face="terminal,monaco" size="2">48.3516 </FONT><BR /><FONT face="terminal,monaco" size="2">-1.35193 </FONT><BR /><FONT face="terminal,monaco" size="2">0.0224839 </FONT><BR /><FONT face="terminal,monaco" size="2">-0.000180263 </FONT><BR /><FONT face="terminal,monaco" size="2">5.39565E-7</FONT></P><P> </P><P>Just put them into a DBL array and use <A href="https://zone.ni.com/reference/en-XX/help/371361M-01/gmath/polynomial_evaluation/" target="_blank">polynomial evaluation</A> to calculate the value for any desired x or array of x's.</P><P> </P><P> </P>Thu, 06 Oct 2016 18:33:21 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355411#M986699altenbach2016-10-06T18:33:21ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355419#M986701
<P>The funny thing and is the main reason I'm not satisfied with this equations is that If I substitute a value above 50 (degrees), the</P><P>calculated resistance its not even close to the real one (from thermistor table). So I'll try the equations you generate and see what happens.</P><P> </P><P>Even thought I'm still figuring out how to use the NONLINEAR VI.... For example I have the next Steinhart-Hart equation:</P><P>1/T = A+B*Ln(R) + C*Ln(R)^3</P><P> </P><P>I've calculated parameters A, B, C:</P><P>A=1.126249 e-3</P><P>B=2.345631 e-4</P><P>C=0.862140 e-7</P><P><IMG src="https://forums.ni.com/t5/image/serverpage/image-id/189892i4FE48367BE1C0EAB/image-size/original?v=v2&px=-1" border="0" alt="Nonlinear VI.png" title="Nonlinear VI.png" /></P><P>I have my X and Y and initial parameters ready. But how do I use this function... Haven't figure it out where to specify the model I'm a bit confused at the moment...</P>Thu, 06 Oct 2016 18:50:54 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355419#M986701JLuna2016-10-06T18:50:54ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355423#M986703
<P>The curve looks much nicer if you take the log of the Y data (and transform back later). Now a 3rd order polynomial is plenty (Just a slight "banana") and you don't get these negative values towards the end.</P><P> </P><P> <IMG src="https://forums.ni.com/ni/attachments/ni/170/986703/1/LogPolynomialFits.png" border="0" alt="" title="" /></P>Thu, 06 Oct 2016 18:53:14 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355423#M986703altenbach2016-10-06T18:53:14ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355426#M986706
<P>The nonlinear equation is basically a third order polynomial using the log(y) and setting the quadratic term to zero. There is no need to complicate things and use levenberg marquardt.</P><P> </P><BLOCKQUOTE><HR /><LI-USER uid="332324"></LI-USER> wrote:<BR /><P> </P><P>I have my X and Y and initial parameters ready. But how do I use this function... Haven't figure it out where to specify the model I'm a bit confused at the moment...</P><HR /></BLOCKQUOTE><P> There are two flavors of the nonlinear curve fit, one using VI model (preferred) and one using a formula. There are plenty of examples that ship with LabVIEW, just look at them!</P>Thu, 06 Oct 2016 18:59:12 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355426#M986706altenbach2016-10-06T18:59:12ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355430#M986709
<P>I just want to know which gives me the most accurate equation...</P><P> </P><P>Many thanks btw <span class="lia-unicode-emoji" title=":grinning_face_with_smiling_eyes:">ðŸ˜„</span></P>Thu, 06 Oct 2016 19:05:21 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355430#M986709JLuna2016-10-06T19:05:21ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355440#M986711
<BLOCKQUOTE><HR /><LI-USER uid="332324"></LI-USER> wrote:<BR /><P>I just want to know which gives me the most accurate equation...\</P><P> </P><HR /></BLOCKQUOTE><P>How accurate are the table values? They have an error too!</P><P> </P><P>Both methods will be similar. the third order polynomial to log(y) is easier to use. The <SPAN>Steinhart-Hart equation</SPAN> inverts the formula buts omits the quadratic term and you need to first rewrite it to solve for R(t).</P><P> </P><P>You simply need to test it. For example if you do my log polynomial and change the order to 5, the maximum difference is below 100 while the values are hundreds of thousands! This is well below your 2% specification (0.04%). Even the third order as suggested earlier gives a max deviation below 0.4%, good enough!</P><P> </P><P>Here's an example for the 5th order (use the right y axis for the scale of the difference between data and fit)</P><P> </P><P> <IMG src="https://forums.ni.com/ni/attachments/ni/170/986711/1/LogPolynomialFits2.png" border="0" alt="" title="" /></P><P> </P><P> </P><P>And here's the difference <STRONG>in percent</STRONG> of the reading:</P><P> <IMG src="https://forums.ni.com/ni/attachments/ni/170/986711/2/LogPolynomialFits3.png" border="0" alt="" title="" /></P><P> </P>Thu, 06 Oct 2016 19:52:19 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355440#M986711altenbach2016-10-06T19:52:19ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355470#M986722
<P>I'm analizing the VI you shared, with log and power of 10 functions. Can you explain why did you choose to do that: first go for</P><P>LOG10 then after using the Polynomial Fit, you introduced data to the POWER10 function.</P><P> </P><P>1 Question came up to mind. You have the POWER10 function affecting ONLY the output "Best polynomial Fit" and you did this</P><P>to be able to see the entire graph correctly... right? Because without it, the Polynomial Fit throws small values due to the previous</P><P>Log10 function. So the thing that confuses me is:</P><P> </P><P>Why is the POWER10 not affecting the Coefficient values output...??</P>Thu, 06 Oct 2016 21:26:33 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355470#M986722JLuna2016-10-06T21:26:33ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355490#M986732
<P>We are fitting the log of the data to a polynomial, thus we need to reverse that to get it into the original mapping. The log is safe because we (hopefully!) never have a negative resistance.</P><P> </P><P>The polynomial coefficients will be correct for the log of the data, so you also need to do 10^x after polynomial evaluation when calculating interpolated data.</P>Thu, 06 Oct 2016 22:26:01 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355490#M986732altenbach2016-10-06T22:26:01ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355698#M986801
<P>Good day altenback,</P><P> </P><P>I'm still a bit confused or more like I haven't quite understand 100% (more like a 80%...) how did it ocurred to you that using a log10 (the power of 10 comes obvious, to get back to the original mapping) would work like a charm. The next is what I understand from this LOG10 method:</P><P> </P><P>- Because the resistance values are so big (almost taking values of 800kohms) if we try to fit this values into a Polynomial equation, when we get to smaller values (for example: 2kohms) the polynomial fit tends to give us possibly negative values. So</P><P>the purpose of the LOG10 method is to work only with positive and small values, so this way the Polynomial FIT analysis tends to give out more accurate POLYNOMIAL COEFFICIENTS... This polynomial coefficients are the "small answer" due to the LOG10; in order to get the real values we have to POWERTO10 the previous values...</P><P> </P><P>So I'm a right, did I get the big picture? I just want to fully understand your explanation. To know when and where apply logarithms, succesfully, pretty awesome way to go \m/.</P><P> </P><P>Thanks for your support I really appreciated @altenbach,</P><P> </P><P>Regards,</P><P> </P>Fri, 07 Oct 2016 14:26:07 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355698#M986801JLuna2016-10-07T14:26:07ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355909#M986872
<P>Yes, the original Y data covers about three orders of magnitude. If you change the mapping of the y axis to logarithmic, it immediately looks much more tame, basically a line with a slight curvature. Obvously, this is much easier to describe with a low oder polynomial. (If it were a pure single exponential, it would be a straight line in the log mapping).</P><P> </P><P>A polynomial is typically a descriptive tool and the coefficients often don't have a direct scientific meaning. So if taking the log makes the curve more suitable for polynomial fitting there is no reason not to use it. Note that you can use the natural log (base e) or log10 (or any other base), it does not matter as long as you undo it the corresponding way later.</P><P> </P><P>Note that you probably want to convert from resistance to temperature (and not the other way around), so just swap the x and y inputs and take the log of the resistance.</P><P> </P><P>Attached is a simple draft for one of your datasets.. when you run it(and whenever the order is changed), it calculates the polynomial of the desired order, then you can select any resistance and read the corresponding interpolated (or extrapolated) temperature. Modify as needed.</P><P>(also note that if you don't take the log, the polynomial fit will probably fail.)</P><P> </P>Sun, 09 Oct 2016 05:06:21 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355909#M986872altenbach2016-10-09T05:06:21ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355937#M986888
<P>Of course with a bit more effort you can implement a nonlinear fit to the Steinhart-Hart equation. Now you get much better than 0.02 degrees difference with only three parameters. (The disadvantage is that you need to create a model VI and have reasonable parameter guesses for the fit.)</P><P> </P><P><IMG src="https://forums.ni.com/ni/attachments/ni/170/986888/2/SteihartHartNonlinFit.png" border="0" alt="" title="" /></P>Sat, 08 Oct 2016 18:17:55 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3355937#M986888altenbach2016-10-08T18:17:55ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356141#M986983
<P>Everything is ok,except for the fact, that now you saying that is "recommended to convert from resistance to temperature (and not the other way around).... But why is that? I've been previously being doing this and everything seems ok... So why the recommendation, I don't get it... Is it the predicted equation less accurate??</P><P> </P><P>Regards,</P>Mon, 10 Oct 2016 12:52:22 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356141#M986983JLuna2016-10-10T12:52:22ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356149#M986987
<P>Hi JLuna,</P><P> </P><P style="padding-left: 30px;"><FONT color="#FF0000">is "recommended to convert from resistance to temperature (and not the other way around).... But why is that?</FONT></P><P>Usually you measure the resistance of your thermistor and want to calculate the temperature from this valueâ€¦</P>Mon, 10 Oct 2016 13:01:57 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356149#M986987GerdW2016-10-10T13:01:57ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356243#M987023
<P>The reason I came up with this problem is because:</P><UL><LI>Based on a detected temperature I need to be in certain levels of NTC resistance. So my question is, if I use the original structure, been the Resistance values - "x" and the respective temperature values - "f(x)" .... Is there an inconvinience with the calculated Polynomial Fit Curve Equation...??</LI></UL>Mon, 10 Oct 2016 16:10:59 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356243#M987023JLuna2016-10-10T16:10:59ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356257#M987027
<P>The polynomial solution should work well both ways.</P><P> </P><P><EM>(Programming the inverse Stainhart-Hart equation is a bit more tricky).</EM></P>Mon, 10 Oct 2016 16:46:20 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356257#M987027altenbach2016-10-10T16:46:20ZRe: How to calculate the equation from dataset using "Fitting VI's" (polynomial or nonlinear Fit) ?
https://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356907#M987210
<P>Sir. Many thanks for your help, I really appreciate it!!</P><P>Best regards!</P><P> </P>Wed, 12 Oct 2016 01:09:31 GMThttps://forums.ni.com/t5/LabVIEW/How-to-calculate-the-equation-from-dataset-using-quot-Fitting-VI/m-p/3356907#M987210JLuna2016-10-12T01:09:31Z