FYI, the VI from the article about system calibration for SCXI involves using a thermocouple calibrator bath and is only as accurate as the the bath and only valid in the range that the bath can operate in. However, using a bath in this manner is a means to precisely transfer the accuracy of a bath to an entire thermocouple measurement system including the thermocouple transducers themselves and the cold junction compensation.
Using an ice bath is a nice way to get a single point calibration (something akin to an offset calibration but at a system level), however ice baths are not as simple as a cup of ice water. NIST can provide guidelines on how to make an ice bath, but I'll summarize some key points A) Use distilled water to make the ice, B) Avoid all contaminants such as salt accumulated on skin, C) shave the ice to make something like a giant snow-cone, D) Add a little distilled water (just enough so that there's something to put the probe into, E) Poke a hole in the snow cone several inches deep to get to the water level, F) Wait 15 minutes, G) Insert the thermocouple so that it is immersed in the liquid water but not touching the ice surrounding it.
It's a fairly involved process, so I would recommend either using thermocouples and modules with specs good enough to get you where you need to go, or investing in a sufficiently accurate thermocouple bath calibrator so you can do the system calibration. But just a warning, it's not a trivial task to do that kind of calibration and you can only go as wide in temperature as the bath allows. Thermocouple vendors are able to go farther out in temperature (beyond 150 degrees Celsius or so) by comparing to RTDs (up to several hundred degrees Celsius), or by using physical state changes of other materials such as the melting point of tin or copper, blockbody radiation thermometry or other means. That's beyond the capabilities of average mortals so I would recommend trying to avoid it.
Daniel
NI - Conditioned Measurements
