Under the auspices of the Inter-american Metrology System (SIM), the National Institute of Standards and Technology (NIST) initiated a regional comparison for type K thermocouples from 100 deg. C to 1100 deg. C, with 11 participating countries. Each participating laboratory was sent new, unused wire from a lot of material characterized by NIST. The high uniformity eliminated any need to correct for variations of the transfer standard among the laboratories, greatly simplifying the analysis. The level of agreement among the laboratories results was quite good. Of the 380 total bilateral combinations of the data at the eight test temperatures, only 13 (i.e., 3.4 % of all combinations) are outside the k = 2 limits, and of these 13, only 3 are outside k = 3 limits. All of the outliers occur at temperatures of 800 deg. C and below, which suggests that drift of the type K wire due to high-temperature oxidation did not cause changes in thermocouple emf comparable to or larger than the claimed uncertainties.
Pub Type: Journals
comparison, temperature, thermocouple, type K