Large-Group Proficiency Testing on Calibration of Platinum Resistance Thermometers from − 196 °C to 650 °C

Proficiency testing on calibration by comparison of platinum resistance thermometers (PRTs) among several calibration laboratories in Korea was conducted. The challenges faced in organizing this proficiency testing were the required wide temperature range (from − 196 °C to 650 °C) and the large number of participants (43). Maintaining the stability of the test items was key to achieving the goal of proficiency testing because the uncertainty of the reference value should be considerably smaller than the uncertainty of the participants’ calibration. For the proficiency testing, four PRTs that meet the criteria specified in the International Temperature Scale of 1990 were used as test items and were circulated among the four groups into which the participants had been divided. The PRTs were calibrated at fixed points between the triple point of argon (− 189.3442 °C) and the freezing point of aluminum (660.323 °C) before and after circulation to the participants, and the PRTs where checked for stability at the mid-point of the circulation. It was possible to maintain the expanded uncertainty of the reference value to less than 18 mK, for which the instability of the test items was a dominant factor. It was found that among the 322 calibration points, 35 calibration points (11%) resulted in normalized error (|En|) > 1. The number of participants who had at least one calibration point with |En|> 1 was 15 (35%).