leitmotif
Member
If your RTD/IO card system is repeatable you can compensate for the input card issues.
Use an ice bath, boiling water, and a known high accuracy thermometer. (The thermometer is needed because boiling and melting points vary with barometric pressure.) Even better if you can use a medium close the temperature you will be measuring.
At any rate, if you can take the output of the temperature of the IO card and create a correction factor. This will probably be an offset to the reading to correct to the "actual" temperature. This will have to be done for each RTD and IO card, and if the RTD is changed in the future will have to be repeated.
Tom
Looked at your statement re boil point and freeze point of water re pressure. I thought the freeze point was a constant and not affected by temperature change. So I looked it up. I think we can agree the effect of pressure change on boil point is much more than that on the freeze point. The bottom line is the effect on freeze point is nearly neglibible and only in the case of looking for or calibrating for 0.1 C tolerance is there any need to measure it.
" When are the boiling temperature and freezing temperature equal?
For all substances, as we lower pressure, the boiling temperature falls much more rapidly than does the freezing temperature. (For water, the freezing temperature rises slightly at low pressure.) Hence the obvious question: Are the boiling temperature and freezing temperature ever equal?
The answer is yes. At the low pressure of 611 Pa (only 0.006 times atmospheric pressure), pure water boils at 0.01 °C, and it also freezes at 0.01 °C. The combination of conditions (P, T) = (611 Pa, 0.01 °C) is called the triple point of water because, at this pressure and temperature ice, liquid water and steam can coexist in equilibrium. This point is used to define our scale of temperature: by definition, the triple point of water occurs at 273.16 K, where K is the kelvin. 273.16 K = 0.01 °C
Full article athttp://www.animations.physics.unsw.edu.au/jw/freezing-point-depression-boiling-point-elevation.htm#pressure
Dan Bentler