Sorry guys, I was a bit misleading, that chart was a first attempt, I had not insulated the leads very well or the thermal paste was contaminated with some AS. It was giving quite a large error for T1
I redid the sensor insertion and capped with epoxy instead of nail polish, it was more in agreement with the in air behaviour after that so I am happy that this is now OK.
This looks pretty linear but when you look closely, removing the slope it does not look as good:
T1 has a 4th order polynomial trend fit, T2 a 2nd order.
You could probably use a second order quite happily, I am using the 4th because of habit, I tend to use this with some more complex curves than this, it can handle more curve inflexions. Both would work in this case, but you can see why a linear fit would not.
The effect of correction on T1 only (for clarity)
And the adjusted response curve. T1 corrected and uncorrected.
Les, re interpolation. It most certainly would work. In fact it would probaly be more accurate but in the interests of speed when dealing with lot of data I find it convenient to use this kind of correction. A little more complex if you are not used to it (I do this kind of stuff every other day) but with intelligent Excelling it is much faster.
Hope this clarifies a few things.
Cheers
Incoherent