No.3（2008）12.Improvement of the Characteristics of Au/Pt Thermocouples

Masashi Sasaki, Masahiko Gotoh

Thermocouples are widely used in many industrial fields. Platinum rhodium alloy thermocouples have been used as standard thermocouples for many years. However these drift significantly, due to selective oxidation of the rhodium component in a high temperature environment. Among currently available thermocouples, although Au/Pt thermocouples are most accurate in terms of repeatability and stability, fragility of their stress relieving coil sometimes limits the fields in which they can be usefully applied. In this study, the improvement of ruggedness of Au/Pt thermocouple was attempted by eliminating the stress relieving coil. Stability of the improved Au/Pt thermocouple was achieved to within 20mK at silver fixed point after 600 hours exposure to high temperatures up to 960 ℃. Its immersion profile is improved to within 12mK over 100mm measured in a silver fixed point cell. This profile is as good as that of a conventional Au/Pt thermocouple with stress relieving coil and is far better than that of a platinum rhodium alloy thermocouple.

Keywords

Au/Pt thermocouple, loop structure, stability improvement

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