Study of the immersion characteristic of thermocouples with a heat-pipe up to 960°C

In this paper results of the measurements on the irregular thermal EMF by means of the thermoelectric scanning are reported. Scanning is carried out in the pressure controlled heat pipe at 960°C over 50 cm along the thermocouples. Measurement was performed with an Au/Pt, two Pt/Pd and a multi-element wire thermocouples. One of the Pt/Pd thermocouples was subjected to 500 hours exposure to 1300°C air environment. The other Pt/Pd thermocouple is a newly fabricated one and act as the reference. The study found no significant difference in the spurious Emf between the two Pt/Pd thermocouples. Discrepancy due to the different immersion was 55 mK for the two Pt/Pd at most. This result suggests that they are superior to the type S and R thermocouples in terms of the immersion characteristics. It is very important to access the source of uncertainty of thermocouples due to the different immersion profile of the furnace. The study provides more realistic information for this purpose.