A simple calibration method of thermocouples is described. An apparatus was constructed and Constantan vs. Chromel thermocouple was used. Its handling and temperature-emf curve are mentioned.
The apparatus is a continuous flow cryostat and temperature in sensor is controlled by flow rate of liquid N2 (or He) and heater. Absolute values of temperature were determined with vapor pressure thermometer. Both junctions of thermocouple thermometers were soldered with silver solder without twisting. Wood's metal solder was used to install dissimilar junctions on sensor. Liquid nitrogen is useful as the reference junction point because of the stability in its boiling temperature. Temperature region of calibration is below 80K. In calibration and application, the same measuring intruments were used.
Obtained emfs are a little less than the NBS-data. And temperature deviation from obtained curves is ±0.5K at 20K. But when we applied those with vapor pressure thermometer, indicated temperatures between two thermometers were almost the same. It is, therefore, considered that calibrated thermocouples have reproducibility. Formulation of data will make it possible to record temperatures automatically.
