RPCoyle:
I would take what dc42 said seriously about making sure you have a correct temp standard to calibrate against..I have been playing around with thermocouples for quite some time and have found that the difference in readings from one to another can vary quite a bit more than specs.
If I want to do a calibration, I use a very accurate mercury thermometer. I usually take an ice point ( 0c) and a boiling point ( which will vary with external pressure but can be calculated) and they do not drift or pick up noise like some of the electronic devices I have tried.
So taking both the reply posted by dc42 and RPCoyle:
I should take callibration point with Ice point and Boiling point and try to adjust the nominal resistance till i get the correct value, is that correct??
DVDdoug:
You can do the calibration in software. Typically when calibrating a "straight line", there is an offset adjustment at zero (or at the bottom of your range). The offset is a constant correction-value added/subtracted from each reading. In other words, the offset adjustmet shifts the curve (or line) up or down without affecting the slope.
Then the top of the range there is usually calibrated with a gain adjustment. i.e. A constant correction-value multiplied by each reading. In other words, the gain adjustment adjusts the slope of the curve/line.
If you want the most accuracy at room temperature (or somewhere in the middle of the range), you may want to make that one of your calibration-points, instead of using the high-low end-points.
Sometimes, there are different corrections (calibrations) for different segments of the curve/line. But, you have to be careful not to introduce a discontinuity, where your correction value suddenly jumps and the reading could jump down, when the temperature goes up, etc.
That seems quite interesting, introducing a gain value and calculating the offset directly from the software.
To DVDdoug:
Can you please kindly guide me where to start, atleast with an equation and how will i be able to calculate the offset and find the proper gain value.Where do i need to integrate the gain value in my actual equation?
Thanks
Taz ...