Abstract

For noble metal thermocouples, thermoelectric inhomogeneity is the most important factor of the calibration uncertainty. For type R and S thermocouples, it is possible to perform a scan at low temperature of around 200 °C, and extrapolate the calculated inhomogeneity to a higher temperature range. However, there has been little experimental study on the thermoelectric scan of type B thermocouples covering low temperature to high temperature of about 1000 °C. In order to determine the practical temperature dependence of the inhomogeneity of type B thermocouples, two used thermocouples were selected and tested from 180 °C to 960 °C based on the single temperature gradient immersion technique. Two liquid baths, one a silicon oil bath at 180 °C and the other a salt bath at 400 °C, were used, and a sodium-heat pipe furnace was used above 600 °C with intervals of around 120 °C. The tested thermocouples generated large emf variations with the immersion depth, and the amount of the variation increased with the test temperature. The calculated inhomogeneity showed the largest value at the lowest temperature, and decreased gradually with increasing temperature to 600 °C. Above this temperature, the inhomogeneity was nearly constant with temperature change, indicating that it was possible to extrapolate the uncertainty due to the inhomogeneity at 600 °C to higher temperatures. From the measured results, it was recommended that a thermoelectric scan be performed at a temperature of at least 600 °C using the sodium-heat pipe furnace to obtain a small calibration uncertainty of a type B thermocouple.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call