No.2（2007）1.Uncertainty evaluation of the temperature controlled bath as the reference junction of thermocouples

Haruhiko Numajiri, Masashi Sasaki, Jun Ode

To satisfy the requirement of Japan Calibration Service System, in addition, to improve the work efficiency of the thermocouple calibration, we have developed the automatic calibration system in Tokyo Metropolitan Industrial Technology Research Institute.

However the reference junction is necessary for the thermocouples and it is important to maintain the reference junction of thermocouples at 0 ℃ continuously during the thermocouple calibration. In case of using crushed ice and water, we must replenish them at intervals of 1 or 2 hours because ice melts. With this, it is not easy to say that the work efficiency improvement was able to be attempted even if the automatic calibration system is developed. On the other hand using an automatically operating ice-point device, it is difficult to say that the reference junction is maintained at 0 ℃ because the insertion depth cannot be secured with certainty. With this, correspondence to various thermocouples used in the industry becomes difficult.

Then, the temperature controlled bath that is able to be driven continuously was decided to be used as the reference junction of the thermocouple. Moreover NMIJ, that is National Metrology Institute of Japan, is using the triple point of water maintenance bath in the same usage, and they say that the stability of that water bath had a standard deviation of 0.5 mK at 0 ℃.

Then we also use TPW maintenance bath as the reference junction, confirmed the efficacy as the reference junction and evaluated its uncertainty.

Keywords

thermocouple, reference junction, uncertainty

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