Use of Salt Baths in the Temperature Range from 175 °C to 540 °C with Uncertainties of Less than 30 m°C

Abstract

Calibration of thermometers in the temperature range from −80 • C to 550 • C requires liquid baths; alcohol, water, silicon oil, salt baths and dry block furnaces. In this study, the use of salt baths outside of their usual range of 250 • C to 540 • C for calibrating thermometers in the range between 175 • C and 250 • C is proposed. The calibration range from 150 • C to 250 • C is usually covered by an oil bath, but utilizing a salt bath saves calibration time and resources, improves stability and homogeneity, allows longer term usage of the liquid, and reduces hazardous chemical vapors evaporated at temperatures above 175 • C. This proposal is based on a study of the uncertainty contributions at varying salt bath temperatures in the range from 175 • C to 540 • C which was carried out in this study. Results achieved and analyzed in this study indicate that the implementation of salt baths in this lower temperature range provides opportunities to calibrate reference and/or working thermometers with an uncertainty below 30 m • C, almost the same as the oil-bath uncertainty in the range of 175 • C to 250 • C. The main components of uncertainty contributed by a salt bath over this temperature range are discussed in this study.