temperature curve fitting

[DavidLee]

Hello ,

I use K type T/C to measure the temperature of an iron steam palette , using high-temperature adhesive tape to fix the T/C hot side on the iron palette .

when acquiring the temperature data , show them on a cvi's application .The problem is that there many sawtooth (dithering)on the measured curve . I want to eliminate these dithering so that I can get a smooth curve . Can use curve fitting method to resolve the problem ? if it can , how to create the H matrix ? your advise is greatly appreciated .

David

[Aaron B.]

Hello David,

You can use the curve fitting CVI function, PolyFit(), to find the coefficients that best represent the polynomial fit of your data points. It takes as inputs the coordinates of your data, the number of data points, and the order for the polynomial you wish to find. It outputs an array of coefficients as well as actual data points on the curve and the mean squared error. The function uses the least squares method and will create an H matrix internally. For the specific syntax of PolyFit(), see the CVI help menu.

To enhance the performance of the function and to avoid unstable results, it is important to normalize the range of your input and chose a reasonable order that is not too great. For a more detailed explanation this, see our KnowledgeBase
0VIF2UTL that can be found by searching our website at www.ni.com/support, or click on the link below:

http://ae.natinst.com/operations/ae/public.nsf/fca7838c4500dc10862567a100753500/45c2016c23b3b0298525645f0073b828?OpenDocument

I hope that you find this information useful and wish you good luck with your application. Take care!

Aaron B.
National Instruments

[DavidLee]

Hi Aarron ,

The temperature is controlled by a thermostat , once the temperature goes beyond a limit , the thermostat will open or close ,so the temperature is also a broke line . Can use PolyFit()to fit such a curve ?


David

[Aaron B.]

Hi David,

Polyfit() takes as an input an array of values that are points that you are trying to fit a curve to. Another input array corresponds to the index of those values (one to one correspondence). So the effective input to the function is a series of points and their coordinates on your graph. Therefore, it should not matter if there are gaps in the actual graph, because you are only inputting discrete points anyways.

Take care and good luck!

Aaron B.
National Instruments

[Joel]

Download a free trial of TableCurve 2D from
http://www.systat.com/products/TableCurve2D/
This will take care of your calibration and curve fitting in seconds
without programming.

- Joel


davidLee wrote in message news:<50650000000800000009C90000-1079395200000@exchange.ni.com>...
> Hello ,
>
> I use K type T/C to measure the temperature of an iron steam palette ,
> using high-temperature adhesive tape to fix the T/C hot side on the
> iron palette .
>
> when acquiring the temperature data , show them on a cvi's application
> The problem is that there many sawtooth (dithering)on the measured
> curve . I want to eliminate these dithering so that I can get a smooth
> curve . Can use curve fitting method to resolve the problem ? if it
> can , how to create the H
matrix ? your advise is greatly appreciated